Maharashtra State Board Class 9 Science Solutions Chapter 16 Heredity and Variation
Class 9 Science Chapter 16 Heredity and Variation Textbook Questions and Answers
Q.1. Fill in the blank and rewrite the completed statements :
1. Organisms produced by show minor variations.
Ans Organisms produced by asexual reproduction show minor variations.
2. The component which is in the nuclei of cells and carries the hereditary characteristics is called …………… .
Ans The component which is in the nuclei of cells and carries the hereditary characteristics is called
chromosomes.
3. ‘……………’ which contain the information about hereditary characteristics in coded form are located on chromosomes.
Ans ‘Genes’ which contain the information about hereditary characteristics in coded form are located on chromosomes.
4. Organisms produced through show major variations.
Ans Organisms produced through sexual reproduction show major variations.
5. Person suffering from down syndrome has chromosomes.
Ans Person suffering from down syndrome has 47 chromosomes.
6. Chromosomes are mainly made up of …………… .
Ans Chromosomes are mainly made up of DNA.
7. Except the allosomes , all other chromosomes are called ‘. ’.
Ans Except the allosomes, all other chromosomes are called ‘autosomes’.
8. The branch of biology which studies the transfer of characteristics of organisms from one generation to the next, and genes in particular, is called ‘. ’.
Ans The branch of biology which studies the transfer of characteristics of organisms from one generation to the next, and genes in particular, is called ‘genetics’.
9. The RNA molecule which, according to the message of the mRNA carries the amino acid up to the ribosomes is called RNA.
Ans The RNA molecule which, according to the message of the mRNA carries the amino acid up to the ribosomes is called transfer RNA.
10. Each strand in the molecule of DNA is made up of many small molecules known as ‘…………’.
Ans Each strand in the molecule of DNA is made up of many small molecules known as ‘nucleotide’.
11. Chromosomes are mainly made up of as genetic component.
Ans Chromosomes are mainly made up of DNA as genetic component.
12. Diseases or disorders occurring due to abnormalities in and mutations in genes are called genetic
disorders.
Ans Diseases or disorders occurring due to abnormalities in chromosomes and mutations in genes are called genetic disorders.
13. In chromosomal condition becomes , in Klinefelter syndrome.
Ans In chromosomal condition becomes 44 + XXY, in Klinefelter syndrome.
14. The structure in the nucleus of cells that carries the hereditary characteristics is called the …………… .
Ans The structure in the nucleus of cells that carries the hereditary characteristics is called the chromosome.
15. Mitochondrial DNA may become defective due to in genes.
Ans Mitochondrial DNA may become defective due to mutation in genes.
16. Transfer of characteristics from parents to offspring is called …………… .
Ans Transfer of characteristics from parents to offspring is called heredity.
17. Genetic name of the pea plant is …………… .
Ans Genetic name of the pea plant is Pisum sativum.
18. Hereditary characters are transferred from parents to offsprings by ……………, hence they are said to be structural and functional units of heredity.
Ans Hereditary characters are transferred from parents to offsprings by gene, hence they are said to be structural and functional units of heredity.
Q.2. Find the odd one out :
1. Mutation in a single gene.
Down syndrome, Turner syndrome, Albinism, Klinefelter syndrome.
Ans Albinism
Albinism is cause of single gene mutation while others are chromosomal abnormalities.
2. Traits of pea plant.
colour of stem, colour of pod, shape of pod, colour of the flower.
Ans colour of the stem
It is not a dominant or recessive trait while other traits can be dominant or recessive.
3. Dominant and recessive trait in a pea plant. Inflated pod, Yellow pod, Tall plant, Round seed.
Ans Yellow pod
It is a recessive trait while remaining are dominant traits in a pea plant.
4. Genetic material.
tRNA, mRNA, rRNA, DNA
Ans DNA
Dna is a genetic material which is herediatary while remaining are types of RNA which are are not herediatary.
5. Dominant and recessive trait in a pea plant.
Green seed, purple flower, Terminal flower, dwarf plant.
Ans purple flower
It is a dominant trait while remaining are recessivetraits in a pea plant.
Q. 3. Find co-related terms 9
1. Klinefelter syndrome : 44+XXY :: Turner syndrome : ?
Ans 44 + X
2. 3:1 Monohybrid: : 9:3:3:1 : ?
Ans Dihybrid
3. 44+X:Turner syndrome: :44+XXY:-…………..
Ans 44+X:Turner syndrome: :44+XXY:- Klinefelter syndrome
- Somatic cells : autosomes :: Gametes : ?
Ans Allosomes
- Women : Turner syndrome : : Men : ?
Ans Klinefelter syndrome
- One pair of contrasting characters : Monohybrid cross :: Two pairs of contrasting characters : ?
Ans Dihybrid cross
7 .Single gene mutation : Monogenic disorders : : Multiple gene mutation : ?
Ans Polygenic disorders
8. P : Parental generation :: F : ?
Ans Filial generation
- Similar chromosomes : Homologous :: Dissimilar chromosomes : ?
Ans Heterologous
Q.4. Match the pair : 1
1.
| Column A | Column B | Column C |
| 1. Turner syndrome | a. 44 + X | i. Women are sterile |
| 2. Klinefelter syndrome | b. 45 + XXY | ii. Men are sterile |
| c. 44 + XX | iii. Men are fertile | |
| d. 44 + XXY | iv. Women are fertile |
Ans
| Column A | Column B | Column C |
| 1. Turner syndrome | 44 + X | Women are sterile |
| 2. Klinefelter syndrome | 44 + XXY | Men are sterile |
Q. 5. State True or False: 14
1. DNA is an alkaline substance.
Ans False – DNA is an acid.
2. The centromere is exactly at the mid-point in Telocentric chromosome.
Ans False – The centromere is right at the end of Telocentric chromosome.
3. Information about lipids synthesis is stored in the genes.
Ans False – Information about protein synthesis is stored in the genes.
4. Klinefelter syndrome arises in women due to abnormalities in sex chromosomes.
Ans False – Klinefelter syndrome arises in men due to abnormalities in sex chromosomes.
6. Polygenic disorders arise from a complex interaction between defects in several genes.
Ans Polygenic disorders arise from a complex interaction between defects in several genes. – True
6. Normal haemoglobin has valine.
Ans False – Normal haemoglobin has glutamic acid.
7. Down syndrome is a disorder arising due to single gene mutation.
Ans False – Down syndrome is a disorder arising due to chromosomal abnormality
8. Consumption of tobacco in any form can cause cancer.
Ans Consumption of tobacco in any form can cause cancer. – True
9. Organisms produced by asexual reproduction show major variations.
Ans False – Organisms produced by asexual reproduction show minor variations.
10. In humans, Information necessary for protein synthesis in the cell is stored in DNA.
Ans In humans, Information necessary for protein synthesis in the cell is stored in DNA. – True
11. Chromosomes in women are represented as 44+XY and in men as 44+XX.
Ans False – Chromosomes in women are represented as 44+XX and in men as 44+XY.
12. Chromosomal abnormalities include either increase or decrease in numbers and deletion or translocation of any part of the chromosome.
Ans Chromosomal abnormalities include either increase or decrease in numbers and deletion or translocation of any part of the chromosome. – True
13. The quantity of growth hormones produced by a plant depends upon the efficiency of the concerned enzyme.
Ans The quantity of growth hormones produced by a plant depends upon the efficiency of the concerned enzyme. – True
14. Genetic material is transferred in unequal quantity from parents to progeny.
Ans False – Genetic material is transferred in equal quantity from parents to progeny.
Q.6. Name the following :
1. Name the Any two monogenic disorders.
Ans Albinism, Sickle-cell anaemia
2. Name the Any two types of chromosomes.
Ans Metacentric, Sub-Metacentric , Acrocentric, Telocentric.
3. Name the Any two Disorders due to chromosomal abnormalities.
Ans Down syndrome, Turner syndrome, Klinefelter syndrome
4. Name the Two pyrimidines present in DNA.
Ans cytosine and thymine
5. Name the two nucleic acids present in the cells.
Ans DNA, RNA
6.Name the Any two blood related physiological genetic diseases.
Ans sickle cell anaemia, haemophilia
7. Name the Any two Disorders due to mutations in multiple genes
Ans Cleft lip, cleft palate, constricted stomach, spina bifida (a defect of the spinal cord), diabetes, blood pressure, heart disorders, asthma, obesity.
8. Name the Two purines present in DNA.
Ans Adenine and guanine
9. Name the Two types of Mendelian crosses.
Ans Monohybrid cross and Dihybrid cross
Q.7. Multiple Choice Questions 20
1. Principles of heredity were given by ……………
A Francis Crick b. Watson c. Mendel d. Mischer
Ans Option c.
2. Consumption of tobacco in any form can cause ……………
A Albinism b. Mitochondrial disorder
c. Cancer d. Diabetes
Ans Option c.
3. Each rung of the ladder is a pair of nitrogenous bases joined by bonds.
a. oxygen b. nitrogen c. hydrogen d. phosphoric
Ans Option c.
4. During fertilization, mitochondria are contributed by ……………
A female gamete b. male gamete
c. endosperm d. male cytoplasm
Ans Option a.
5. Diseases or disorders occurring due to abnormalities in and mutations in genes are called genetic
disorders.
A RNA b. Chromosomes c. Ribosomes d. mRNA
Ans Option b.
6. In sickle cell anemia, the which are normally biconcave become sickle-shaped.
A plama cells b. Platelets c. WBC s d. RBCs
Ans Option d.
7. Following fig shows which of the following?
a. types of ribosomes b. structure of DNA possible
c. types of RNA d. structure of RNA
Ans Option c.
8. Adenine always pairs with in RNA.
a. uracil b. cytosine c. thymine d. guanine
Ans Option a.
9. This chromosome look like the English letter ‘i’. Which of the following is this?
a. Metacentric b. Telocentric
c. Acrocentric d.Sub-Metacentric
Ans Option b.
10. Harmful effects of smoking are due to the present in tobacco.
a.biotin b. smoke c. carbon d. nicotine
Ans Option d.
11. Chromosomes in men are represented as …………… .
a. 45+XY b. 44+X Y c. 44+XXY d. 44+XX
Ans Option b.
12. Except the allosomes, all other chromosomes are called ‘. ’.
a. . sex-autosomes b. autosomes
c. heterologous chromosomes d. homologous chromosomes
Ans Option b.
13. Which of the following are called ‘Master Molecules’?
a. Chromosomes b. nucleotide
c. mRNA d. DNA
Ans Option d.
14. 23rd pair of chromosome in humans is known as …………….
a. allosome b. autosome
c. chromosome d. centromere
Ans Option a.
15. Arrangement of DNA is in the form of
a. linear b. spiral c. single helix d. double helix
Ans Option d.
16. What is chromosome mainly made of ?
a. DNA and RNA b. protein and rRNA
c. protein and mRNA d. protein and DNA
Ans Option d.
17. If one end of the DNA strand is sugar molecule the other end will have
a. RNA b. anti-sugar molecule
c. nitrogenous base d. phosphoric acid
Ans Option d.
18. Which of the following has only one arm?
a. Telocentric b. Metacentric
c. Acrocentric d. Sub-Metacentric
Ans Option a.
19. The segment of DNA which contains all the information for synthesis of a particular protein is called a ‘. ’ for that protein.
- gene b. trait c. chromosome d. DNA protein
Ans Option a.
a. Sub-Metacentric b. Metacentric
c. Acrocentric d. Telocentric
Ans Option c.
Q.8. Write Short Notes 10
1. Down syndrome
Ans i. Down syndrome is a disorder arising due to chromosomal abnormality. This is the first discovered and
described chromosomal disorder in human beings.
ii. This disorder is characterised by the presence of 47 chromosomes. It is described as trisomy of the 21st chromosome.
iii. Infants with this disorder have one extra chromosome with the 21st pair in every cell of their body. Therefore they have 47 chromosomes instead of 46.
iv.Children suffering from Down’s syndrome are usually mentally retarded and have a short lifespan. Mental retardation is the most prominent characteristic.
2. Write note on use of DNA finger printing.
Ans 1. DNA finger printing is technique in which the sequence of the genes in the DNA of a person i.e. the genome of the person is identified.
- It is useful to identify the lineage and to identify criminals because it is unique to every person.
- It is very useful in forensic science to solve many cases.
3. Polygenic disorders.
Ans i. Some disorders arise due to mutations in more than one gene. In most such disorders, their severity increases due to effects of environmental factors on the foetus.
ii. Common examples of such disorders are cleft lip, cleft palate, constricted stomach, spina bifida (a defect of the spinal cord), etc.
iii. Besides, diabetes, blood pressure, heart disorders, asthma, obesity are also polygenic disorders.
iv. Polygenic disorders do not strictly follow Mendel’s principles of heredity. These disorders arise from a complex interaction between environment, life style and defects in several genes.
4. Monogenic disorders.
Ans i. Disorders or diseases occurring due to mutation in any single gene into a defective one are called monogenic disorders.
iii. Approximately 4000 different disorders of this type are now known. Due to abnormal genes, their products are either produced in insufficient quantity or not at all.
Iii .It causes abnormal metabolism that may lead to death at a tender age.
iv.Examples of such disorders are Hutchinson’s disease, Tay-Sachs disease, galactosaemia, phenylketonuria, sickle cell anaemia, cystic fibrosis, albinism, haemophilia, night blindness, etc.
5. Albinism
Ans i. Albinism is a genetic disorder.It is caused to due mutation in a single gene and thus, a monogenic disorder.
ii. Our eyes, skin and hair have colour due to the brown pigment, melanin.
iii. In this disease, the body cannot produce melanin.
iv. The skin becomes pale, hairs are white and eyes are usually pink due to absence of melanin pigment in the retina and sclera.
Q. 9. Attempt the following. 8
1. Match the column.
| Column A | Column B | Column C |
| 1. Leber hereditary optic neuropathy | a. Turner syndrome | i. Effect on blood-glucose level |
| 2. Diabetes | b. Mitochondrial disorder | ii. Men are sterile |
| c. Monogenic disorder | ii. white hairs | |
| d. Polygenic disorder | iv. This disorder arises during development of zygote. | |
Ans
| 1. Leber hereditary optic neuropathy | Mitochondrial disorder | This disorder arises during development of zygote. |
| 2. Diabetes | Polygenic disorder | Effect on blood-glucose level |
2. Label the Diagram
Ans
3. Match the columns.
| Column A | Column B | Column C |
| 1. Albinism | a. Trisomy of 21st Chromosome | i. Pale skin, white hairs |
| 2. Down
syndrome |
b. Monosomy of X chromosome | ii. Women are sterile |
| c. Monogenic disorder | iii. 21st pair in every cell of their body. | |
| d. Polygenic disorder | iv. This disorder arises during development of zygote. | |
Ans
| 1. Albinism | Monogenic disorder | Pale skin, white hairs |
| 2. Down syndrome | Trisomy of 21st Chromosome | 21st pair in every cell of their body |
4. Identify the type of the chromosome.
Ans i. Metacentric
ii. Sub-metacentric
iii .Acrocentric
iv. Telocentric
Q. 10. Complete the given flow chart / table / diagram 6
1. Complete the tree diagram below based on types of
hereditary disorders.
Ans
2. Fill the given table by the type of chromosome present based on the position of the centromere.
| Position of centromere | Type of chromosome |
| Exactly at the mid-point | …………… |
| End of this chromosome | …………… |
| Near one end of this chromosome | …………… |
| Somewhere near the mid-point | …………… |
Ans
| Position of centromere | Type of chromosome |
| Exactly at the mid-point | Metacentric |
| End of this chromosome | Telocentric |
| Near one end of this chromosome | Acrocentric |
| Somewhere near the mid-point | Sub-metacentric |
3. Fill the given table by the reason occuring for the mentioned diorder.[chromosomal abnormality, single or multiple gene disorder]
| Disorder | Reason for the disorder |
| Klinefelter syndrome | …………… |
| Constricted stomach | …………… |
| Sickle-cell anaemia | …………… |
| Turner syndrome | …………… |
Ans
| Disorder | Reason for the disorder |
| Klinefelter syndrome | Chromosomal abnormality |
| Constricted stomach | Multiple genes mutation |
| Sickle-cell anaemia | Single gene mutation |
| Turner syndrome | Chromosomal abnormality |
Q.11. Distinguish between: 6
1. Monohybrid cross and Dihybrid cross.
Ans:
| Monohybrid cross | Dihybrid cross | |
| i. | In the monohybrid cross, one pair of contrasting characteristics are under consideration. | In the dihybrid cross, two pairs of contrasting characteristics are under consideration. |
| ii. | The phenotypic ratio is 3:1 | The phenotypic ratio is 9:3:3:1 |
| iii. | F2 generation give 3 genotypes of individuals. | different | types | of | F2 generation give 9 genotypes of individuals. | different | types | of |
| iv. | F2 generation give 2 phenotypes of individuals. | different | types | of | F2 generation give 4 phenotypes of individuals. | different | types | of |
2. . DNA and RNA.
Ans
| DNA | RNA | |
| i. | It is nucleic acid of deoxyribose sugar. | It is nucleic acid of ribose sugar. |
| ii. | DNA is genetic material in almost all organisms. | RNA is not a genetic material except in few viruses. |
| iii. | DNA consists of codes for protein synthesis. | RNA do not code for any protein |
| iv. | It is an hereditary molecule. | It is a non-hereditary molecule |
3. Turner syndrome and Klinefelter syndrome.
Ans
| Turner syndrome | Klinefelter syndrome | |
| i. | It occurs due to presence of an extra X- chromosome. | |
| It occurs due to absence of an X-chromosome. | ||
| ii. | It occurs only in females. | It occurs only in males. |
| iii. | The chromosomes are represented as 44+XXY. | |
| The chromosomes are represented as 44+X. | ||
| iv. | It occurs due to absence of one of the chromosome in a pair. | It occurs due to non-disjunction of the chromosomes. |
Q.12. Give scientific reasons 8
1. It is necessary for people to have their blood examined before marriage.
Ans i. Genetic diseases spread in only one way i.e. reproduction.
ii. Examination of blood would show whether the person is normal or a carrier of sickle-cell anemia gene.
iii. If both are diagnosed with carrier the progeny have risk of having a child suffering with sickle cell anemia, which can be fatal.
iv.Hence, husband and wife should get their blood exmined either before marriage or after it.
2. Organisms produced by asexual reproduction show minor variations.
Ans i. In asexual reproduction, there is no gamete formation. The parent itself forms a new progeny.
ii. As only one parent is involved in the process, the DNA as it is replicated and passed to the daughter cells.
iii. Due to this, there is high similarity between the parent and the progeny.
iv.Therefore, Organisms produced by asexual reproduction show minor variations.
3. When green seeds crossed with yellow seeds, all seeds in F1 generation were found to be yellow.
Ans i. Yellow colour of the seed is dominant over the green colour of the seed of the pea plant.
ii. Dominant charactr is the character which masks the character of the other trait, which is known recessive.
iii. When present is heterologous form,only the dominant character is expressed phenotypically while recessive can be expressed only when in homologous form.
iv. Thus, all seeds in F1 generation were yellow when pure yellow seeds were crossed with green seeds.
4. We should not avoid living with a person suffering from a genetic disorder.
Ans 1. Genetic disorders gets carried further from parents to the next generation.
- They are not contagious and do not spread through contact.
So, we should not avoid living with a person suffering from a genetic disorder.
Q.13. Give examples 8
1. Give any 4 Nitrogen bases in RNA.
Ans Adenine, Guanine, Cytosine, Uracil.
2. Give any 4 Single gene disorders.
Ans Hutchinson’s disease, Tay-Sachs disease, galactosaemia, phenylketonuria, sickle cell anaemia, cystic fibrosis, albinism, haemophilia, night blindness, etc.
3. Give any 4 Nitrogen bases in DNA
Ans Adenine, Guanine, Cytosine, Thymine.
4.Give any 4 Polygenic disorders
Ans Cleft lip, cleft palate, constricted stomach, spina bifida (a defect of the spinal cord), diabetes, blood pressure, heart disorders, asthma, obesity, etc.
Q.14. Explain the statement 15
1. Down syndrome is a disorder arising due to chromosomal abnormality. Explain
Ans i. Down syndrome is the first discovered and described chromosomal disorder in human beings.
ii. This disorder is characterised by the presence of 47 chromosomes.
iii. It is described as trisomy of the 21st chromosome. Infants with this disorder have one extra chromosome with the 21st pair in every cell of their body.
iv. Therefore they have 47 chromosomes instead of 46.
v. Children suffering from Down’s syndrome are usually mentally retarded and have a short lifespan. Mental retardation is the most prominent characteristic.
vi. Other symptoms include short height, short wide neck, flat nose, short fingers, scanty hair, single horizontal crease on palm, and a life expentancy of about 16–20 years.
2. DNA molecules are called ‘Master Molecules’. Explain
Ans i. Chromosomes are mainly made up of DNA. Initially this acid was reported to be only in the nucleus of cells. Hence, it was named nucleic acid. However, it was later realized that it is present in other parts of the cell too.
ii. Molecules of DNA are present in all organisms from viruses and bacteria to human beings. Information necessary for protein synthesis in the cell is stored in DNA.
iii. The segment of DNA which contains all the information for synthesis of a particular protein is called a ‘gene’ for that protein.
iv. Segments of the DNA molecule are called genes. Due to variety in the sequence of nucleotides, different kinds of genes are formed.
v. These genes are arranged in a line. Genes control the structure and function of the cells and of the body.
vi. Also, they transmit the hereditary characteristics from parents to offspring. Hence, they are said to be the functional units of heredity.
vii. These molecules control the functioning, growth and division (reproduction) of the cell and are therefore called ‘Master Molecules’.
3. Nucleotide is a unit structure of DNA. Explain.
Ans i. Each strand in the molecule of DNA is made up of many small molecules known as ‘nucleotide’. There are four types of nitrogenous bases adenine, guanine, cytosine and thymine.
ii. Adenine and guanine are called as ‘purines’ while cytosine and thymine are called ‘pyrimidines’.
iii. In the structure of the nucleotide, a molecule of a nitrogenous base and phosphoric acid are each joined to a molecule of sugar.
iv. As there are four types of nitrogenous bases, nucleotides also are of four types.
v. Nucleotides are arranged like a chain, in a molecule of DNA. The two threads of the DNA molecule are comparable to the two rails of a ladder and each rail is made up of alternately joined molecules of sugar and phosphoric acid.
vi. Each rung of the ladder is a pair of nitrogenous bases joined by hydrogen bonds.
vii. Adenine always pairs with thymine and cytosine always pairs with guanine.Therefore, Nucleotide is said to be the unit structure of DNA.
4. RNA is the second important nucleic acid of the cell. Explain.
Ans i. Ribose nucleic acid is made up of ribose sugar, phosphate molecules and four types of nitrogenous bases adenine, guanine, cytosine and uracil.
ii.The nucleotide i.e. smallest unit of the chain of the RNA molecule is formed by combination of a ribose sugar, phosphate molecule and one of the nitrogenous bases.
iii. Large numbers of nucleotides are bonded together to form the macromolecule of RNA. So it is said that RNA is the second important nucleic acid of the cell.
5. The similarities and differences are all the effect of heredity. Explain
Ans i. Information necessary for protein synthesis in the cell is stored in DNA.
ii. The segment of DNA which contains all the information for synthesis of a particular protein is called a ‘gene’ for that protein.
iii. It is necessary to know the relationship of these proteins with the characteristics of organisms.
iv. To understand the concept of heredity let us consider the characteritic ‘plant height’. We know that there are growth hormones in plants.
v. Increase in height of plants depends upon the quantity of growth hormones. The quantity of growth hormones produced by a plant depends upon the efficiency of the concerned enzyme.
vi. Efficient enzymes produce a greater quantity of the hormone due to which the height of the plant increases.
vii. However, if the enzymes are less efficient, a smaller quantity of hormone is produced leading to a stunting of the plant.
Q.15. Attempt the following. 6
1. Identify the type of RNA and explain them:
Ans Ribosomal RNA (rRNA), Messenger RNA (mRNA) and Transfer RNA (tRNA) are are three types of RNA.
a.Ribosomal RNA (rRNA): The molecule of RNA which is a component of the ribosome organelle is called a ribosomal RNA. Ribosomes perform the function of protein synthesis.
Messenger RNA (mRNA): The RNA molecule that carries the information of protein synthesis from genes
b. i.e. DNA chain in the cell nucleus to ribosomes in the cytoplasm which produce the proteins, is called messenger RNA.
c. Transfer RNA (tRNA): The RNA molecule which, according to the message of the mRNA carries the amino acid up to the ribosomes is called transfer RNA.
- Regarding Monohybrid cross by Mendel, in the second filial generation (F2), both i.e. tall and dwarf types of plants appeared. According to the data collected by Mendel, out of 929 pea plants, 705 were tall and 224 were short. Thus, the phenotypic ratio of these plants is 3(tall):1(dwarf) and genotypic ratio is 1(TT):2(Tt):1(tt). Thus, it can be inferred that in the F2 generation, phenotypically there are two types of plants whereas genotypically there are three types. These types are shown as follows.
F2 Pure dominant (TT) – tall plants [Homozygous] F2 Pure recessive (tt) – dwarf plants [Homozygous] F2 Hybrid plants (Tt) –tall plants [Heterozygous]
Questions–
i. Which character is observed to be dominant?
ii. . In F1 generation which trait is not seen?
iii. Which plant was used in following experimentation?
Ans i. Tall character of plant is observed to be dominant.
- Dwarf trait of the plant is not seen in F1 generation as it is recessive character.
- Pisum sativum (pea plant).
Q.16. Complete the table/ web/ flow chart 9
1. Completed the Table
| Dominant | Recessive | |
| Colour of flower | …………… | …………… |
| Position of flower | …………… | …………… |
| Height of plant | …………… | …………… |
Ans
| Dominant | Recessive | |
| Colour of flower | Purple | White |
| Position of flower | Axillary | Terminal |
| Height of plant | Tall | Dwarf |
- Complete the table
| Short form | Full Form | Functions | |
| i. | rRNA | …………… | …………… |
| ii. | mRNA | …………… | …………… |
| iii. | tRNA | …………… | …………… |
Ans
| Short form | Full Form | Functions | |
| i. | rRNA | Ribosomal RNA | Protein synthesis |
| ii. | mRNA | Messenger RNA | Carries the information from DNA |
| iii. | tRNA | Transfer RNA | Carries the amino acid |
3. Completed the Table
| Dominant | Recessive | |
| Shape of the seed | …………… | …………… |
| Colour of seed | …………… | …………… |
| Shape of pod | …………… | …………… |
Ans
| Dominant | Recessive | |
| Shape of the seed | Round | Wrinkled |
| Colour of seed | Yellow | Green |
| Shape of pod | Inflated | Constricted |
Q.17. Complete the sentences in paragraph 15
- Complete the paragraph:
(adenine, phosphoric acid, centromeres, cytosine, nucleotides, ribonucleic acid, guanine, thymine)
In 1953, Watson and Crick produced a model of the DNA molecule. As per this model, each strand in the molecule of DNA is made up of many small molecules known as …………… . There are four types of nitrogenous bases adenine, guanine, cytosine and thymine. …………… and are called as ‘purines’ while …………… and …………… are called ‘pyrimidines’. In the structure of the nucleotide, a molecule of a nitrogenous base and are each joined to a molecule of sugar.
Ans: In 1953, Watson and Crick produced a model of the DNA molecule. As per this model, each strand in the molecule of DNA is made up of many small molecules known as nucleotides. There are four types of nitrogenous bases adenine, guanine, cytosine and thymine. Adenine and guanine are called as ‘purines’ while cytosine and thymine are called ‘pyrimidines’. In the structure of the nucleotide, a molecule of a nitrogenous base and phosphoric acid are each joined to a molecule of sugar.
2 . Complete the paragraph:
(allosomes, chromosomes, heterologous, somatic, autosomes, homologous , sex)
Generally, in cells chromosomes are in pairs. If the pair consists of similar chromosomes by shape and organization, they are called ‘…………… chromosomes’ and if they are not similar they are called ‘…………… chromosomes’. In case of organisms that reproduce sexually one of the chromosomal pairs is different from all than others. Chromosomes of this different pair are called ‘…………… chromosomes’ or…………… and all other chromosomes are called ‘. ’.
Ans Generally, in somatic cells chromosomes are in pairs. If the pair consists of similar chromosomes by shape and organization, they are called ‘homologous chromosomes’ and if they are not similar they are called ‘heterologous chromosomes’. In case of organisms that reproduce sexually one of the chromosomal pairs is different from all than others. Chromosomes of this different pair are called ‘sex chromosomes’ or allosomes and all other chromosomes are called ‘autosomes’.
- Complete the paragraph.
(functional, DNA, group, hereditary, linearly, calcium, proteins, nucleotides)
Gene is a segment of …………… molecule. Due to variety of sequences of , different kinds of genes are formed. These genes are …………… arranged. It store the information for synthesis of It control the structure and function of the cells and of the body. It transmit the characteristics from parents to offspring. They are also said to be units of heredity.
Ans Gene is a segment of DNA molecule. Due to variety of sequences of nucleotides, different kinds of genes are formed. These genes are linearly arranged. It store the information for synthesis of proteins. It control the structure and function of the cells and of the body. It transmit the hereditary characteristics from parents to offspring. They are also said to be functional units of heredity.
4. Complete the paragraph.:
(Mitochondrial disorder, retina, brown, red, mutation, Albinism, sclera, pink)
…………… is a monogenic disorder. In such disease, due to …………… in gene, body fails to produce…………… pigment melanin. Absence of melanin causes skin to become pale and hairs turn white. Due to absence of melanin pigment in the …………… and ……………, eyes become …………… .
Ans : Albinism is a monogenic disorder. In such disease, due to mutation in gene, body fails to produce brown pigment melanin. Absence of melanin causes skin to become pale and hairs turn white. Due to absence of melanin pigment in the retina and sclera, eyes become pink.
5. Complete the paragraph.
(1995, DNA sequence, diagnosis, 20,000 to 30,000, Cerolo Genomics Corporation, treatment, 30,000 to
40,000, Celera Genomics Corporation, 1990)
Human Genome project was undertaken in , by all the geneticists of world. In June 2000, scientists of this project and …………… collectively announced the discovery of the complete of the human genome. Scientists confirmed the presence of about …………… genes in the human genome. This project helped to identify disease causing genes, due to which proper …………… and of various genetic diseases has become possible.
Ans Human Genome project was undertaken in 1990, by all the geneticists of world. In June 2000, scientists of this project and Celera Genomics Corporation collectively announced the discovery of the complete DNA sequence of the human genome. Scientists confirmed the presence of about 20,000 to 30,000 genes in the human genome. This project helped to identify disease causing genes, due to which proper diagnosis and treatment of various genetic diseases has become possible.
Q. 18. Answer the following 18
1. Define Genetic disorders and explain any three Genetic disorders.
Ans i. Diseases or disorders occurring due to abnormalities in chromosomes and mutations in genes are called genetic disorders.
ii. Chromosomal abnormalities include either increase or decrease in numbers and deletion or translocation of any part of the chromosome. Examples are physical disorders like cleft lip, albinism and physiological disorders like sickle cell anaemia, haemophilia, etc.
iii. Offspring are not sterile if there is change in the number of autosomes or allosomes.Exampole in case of Turner syndrome and Klinefelter syndrome.
iv. If there is an increase in number of any autosomal pair, physical or mental abnormalities arise and the lifespan is shortened with a shortened life span.Example Down syndrome.
v. Monogenic disorders, caused by mustation in a single gene, Examples of such disorders are Hutchinson’s disease, Tay-Sachs disease, galactosaemia, phenylketonuria, sickle cell anaemia, cystic fibrosis, albinism, haemophilia, night blindness, etc.
vi. Mitochondrial DNA may also become defective due to mutation. Leber hereditary optic neuropathy is an example of a mitochondrial disorder.
vii. Sometimes, disorders arise due to mutations in more than one gene. Common examples of such disorders are cleft lip, cleft palate, constricted stomach, spina bifida (a defect of the spinal cord), etc. Besides, diabetes, blood pressure, heart disorders, asthma, obesity are also polygenic disorders.
2. Define chromosome and explain its types.
Ans i. The structure in the nucleus of cells that carries the hereditary characteristics is called the chromosome. It is made up mainly of nucleic acids and proteins.
ii. There are four types of chromosomes.
1. Metacentric : The centromere is exactly at the mid-point in this chromosome, and therefore the chromosome looks like the English letter ‘V’. The arms of this chromosome are equal in length.
2. Sub-metacentric : The centromere is somewhere near the mid-point in this chromosome which therefore looks like English letter ‘L’. One arm is slightly shorter than the other.
3. Acrocentric : The centromere is near one end of this chromosome which therefore looks like the English letter ‘j’. One arm is much smaller than other.
4. Telocentric : The centromere is right at the end of this chromosome making the chromosome look like the English letter ‘i’. This chromosome consists of only one arm.
3. How do specific traits or characteristics appear in organisms?
Ans i. Information necessary for protein synthesis in the cell is stored in DNA.
ii. The segment of DNA which contains all the information for synthesis of a particular protein is called a ‘gene’ for that protein.
iii. It is necessary to know the relationship of these proteins with the characteristics of organisms.
iv. Segments of the DNA molecule are called genes. Due to variety in the sequence of nucleotides, different kinds of genes are formed.
v. These genes are arranged in a line. Genes control the structure and function of the cells and of the body. Also, they transmit the hereditary characteristics from parents to offspring.
Vi, Hence, they are said to be the functional units of heredity. That is why, many similarities are seen between parents and their offspring.
vii. Information about protein synthesis is stored in the genes and this information of traits is poassed on from generation to generation.
4. Write ill effects of consuming tobacco.
Ans i. Many people consume tobacco, either by smoking or by chewing.
ii. Tobacco consumption can also lead to shortening of life span, chronic bronchitis, pericarditis, cancer of the lungs, mouth, larynx (voice box), pharynx, pancreas, urinary bladder, etc.
iii. Harmful effects of smoking are due to the nicotine present in tobacco. It affects the central and peripheral nervous system.
iv. Tobacco smoke contains harmful chemicals like pyridine, ammonia, aldehyde furfural, carbon monoxide, nicotine, sulphur dioxide, etc. They cause uncontrolled cell division.
v. Tobacco smoke is full of minute carbon particles which causes normal tissue of the lung to transform into thickened black tissue. This causes cancer.
vi. While chewing tobacco or tobacco products much of the extract is absorbed into the body. Excessive tobacco consumption may cause cancer of lips or tongue, visual disorders or tremors.
5. Write about the symptoms and treatment of Sickle cell anaemia.
Ans i. Sickle-cell anaemia is a hereditary disease. It occurs due to changes in genes during conception.
ii. Symptoms of this disease are: Swelling of hands and legs, pain in joints, severe general body aches, frequent colds and cough, constant low grade fever, exhaustion, pale face, low haemoglobin content.
iii. The remedies which can be done are only: A carrier or sufferer should avoid marriage with another carrier or sufferer.
iv. Also, a person suffering from sickle cell anaemia should take a tablet of folic acid daily.
6. Why do Turner syndrome occurs only in females?
Ans i. Human beings have 46 chromosomes in the form of 23 pairs. There is great variation in the size and shape of these chromosomal pairs.
ii. These pairs have been numbered. Out of 23 pairs, 22 pairs are autosomes and one pair is of sex chromosomes (allosomes).
iii. Sex chromosomes in women are represented as 44+XX and in men as 44+XY.
iv. Y-chromosome is responsible for the development of males. As in Turner syndrome, only one X-
chromosome is present, it consist of only female characters and thus the individual is female.
v. Turner syndrome (or 44+X) arises due to either inheritance of only one X chromosome from parents or due to inactivation of the gender-related part of X-chromosomes.
vi. Instead of the normal 44+XX condition, women suffering from Turner syndrome show a 44+X condition. Such women are sterile i.e. unable to have children due to improper growth of the reproductive organs.
Q.19. Extra data :
1. Write a dihybrid cross showing the phenotypic and genotypic ratio with any example of traits of a pea plant.
Ans:
2. Heredity.
Ans Transfer of characteristics from parents to offspring is called heredity. New progeny is formed through the process of reproduction. Except for a few minor differences, the offspring shows great similarities with parents.
3. Explain the structure, function and types of RNA.
Ans Structure of RNA:
1.This nucleic acid is made up of ribose sugar, phosphate molecules and any four types of nitrogenous bases adenine, guanine, cytosine and uracil.
- .The nucleotide is smallest unit of the chain of the RNA molecule.
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Large numbers of nucleotides are bonded together to form the macromolecule of RNA. Function of RNA: It performs the function of protein synthesis.
Types of RNA:
4. Ribosomal RNA (rRNA) : The molecule of RNA which is a component of the ribosome organelle is called a ribosomal RNA. Ribosomes perform the function of protein synthesis.
5. Messenger RNA (mRNA) : It carries the information of protein synthesis from genes i.e. DNA chain in the cell nucleus to ribosomes in the cytoplasm.
6. Transfer RNA (tRNA) : It carries the amino acid up to the ribosomes.
4. The branch of biology which studies the transfer of characteristics of organisms from one generation to the next, and genes in particular, is called ‘……………’. New progeny is formed through the process of …………….Except for a few minor differences, the offspring shows great similarities with parents. Organisms produced by …………… reproduction show minor variations. However, offspring produced through …………… reproduction, show comparatively greater variations.
Ans The branch of biology which studies the transfer of characteristics of organisms from one generation to the next, and genes in particular, is called ‘genetics’. New progeny is formed through the process of reproduction. Except for a few minor differences, the offspring shows great similarities with parents. Organisms produced by asexual reproduction show minor variations. However, offspring produced through sexual reproduction, show comparatively greater variations.
5. Dihybrid cross
Ans In the dihybrid cross, two pairs of contrasting characteristics are under consideration. Mendel performed more experiments on hybridization in which he considered more than one pair of contrasting characteristics.
6. Monohybrid cross.
Ans Mendel brought about the cross between two pea plants with only one pair of contrasting characters. This type of cross is called a monohybrid cross.
7. Genetic disorders.
Ans Diseases or disorders occurring due to abnormalities in chromosomes and mutations in genes are called genetic disorders. Chromosomal abnormalities include either increase or decrease in numbers and deletion or translocation of any part of the chromosome.
- Each chromosome is made up of DNA and it appears .. -shaped midway during cell division. There is a constricted region on each chromosome. It is called the ‘Primary constriction’ or ‘. ’. This divides the chromosome into parts. Each part is called an ‘arm’. The centromere has a specific position in each chromosome. Depending upon this, there are types of chromosomes.
Ans Each chromosome is made up of DNA and it appears dumbell -shaped midway during cell division. There is a constricted region on each chromosome. It is called the ‘Primary constriction’ or ‘ Centromere ’. This divides the chromosome into two parts. Each part is called an ‘arm’. The centromere has a specific position in each chromosome. Depending upon this, there are four types of chromosomes.
9. Monogenic disorders.
Ans Disorders or diseases occurring due to mutation in any single gene into a defective one are called monogenic disorders. Due to abnormal genes, their products are either produced in insufficient quantity or not at all.
Q. 20. Answer the following in detail 20
1. Answer the following questions:
i. How are chromosomes represented in males and females?
ii. Do genetic disorders occur only due to Chromosomal abnormalities ?
iii. What are the other reasons for genetic diorders?
iv. How many pairs of autosomes are present in humans?
v. Give two examples of physical and physiological disorders.
Ans i. Chromosomes in women are represented as 44+XX and in men as 44+XY.
ii. No, genetic disorders do not occur only due to Chromosomal abnormalities.
iii. Mutation in single gene, mutations in multiple genes, mitochoindial DNA mutation are other reasons for
genetic diorders.
iv. Humans have 22 pairs of autosomes.
v. Examples of physical disorders are cleft lip, albinism and physiological disorders are sickle cell anaemia, haemophilia, etc.
2. Describe the structure of the DNA molecule.
Ans 1. In 1953, Watson and Crick produced a model of the DNA molecule.
- As per this model, two parallel threads of nucleotides are coiled around each other. This arrangement is called a ‘double helix’.
-
Each strand in the molecule of DNA is made up of many small molecules known as ‘nucleotide’.
-
In the structure of the nucleotide, a molecule of a nitrogenous base and phosphoric acid are each joined to a molecule of sugar.
-
Nucleotides are arranged like a chain, in a molecule of DNA.
-
The two threads of the DNA molecule are comparable to the two rails of a ladder and each rail is made up of alternately joined molecules of sugar and phosphoric acid.
-
Each rung of the ladder is a pair of nitrogenous bases joined by hydrogen bonds.
-
Adenine always pairs with thymine and cytosine always pairs with guanine.
3. Answer the following Questions–
i.What is present in tobacco which leads to harmful effects?
ii.In which two ways is tobacco generally consumed?
iii. Excess tobacco can cause effects on which parts of the body?
iv. What present in tobacco smoke causes blackening of lungs?
v. Name any two chemicals present in tobacco.
Ans i. Nicotine present in tobacco leads to harmful effects.
ii. By chewing and by smoking.
iii. Excessive tobacco consumption may cause cancer of lips or tongue, visual disorders or tremors.
iv. Tobacco smoke is full of minute carbon particles which causes normal tissue of the lung to transform into thickened black tissue.
v. Tobacco smoke contains harmful chemicals like pyridine, ammonia, aldehyde furfural, carbon monoxide, nicotine, sulphur dioxide, etc.
4. Explain Mendel’s monohybrid progeny with the help of any one cross.
Ans i. Mendel’s monohybrid cross involves cross between two pea plants with only one pair of contrasting characters.
ii. Single character i.e. height of pea plant can be considered for the cross. Here, the tallness of plant and dwarfiness of plant are the contrasting characteristics.
iii. The tall plant and dwarf plant are the parents of F1 generation,hence, called P1 or parental generation.
iv. All the plants produced in F1 generation are tall, having genotype Tt. This indicates that gene ‘T’ responsible for tallness in pea plants is dominant over the gene ‘t’ responsible for dwarfness in pea plants.
v. When F1 hybrids are self fertilized they produced second filial generation (F2).
vi. In F2 generation, both tall and dwarf plants appeared in the ration of 3 : 1.
vii. Thus, the phenotypic ration of F2 generation is 3(Tall) : 1 (Dwarf)
viii. The genotypic ration of F2 generation is 1(TT):2 (Tt) : 1 (tt)
