CHSE Odisha Class 12 Biology Solutions Chapter 4 Reproductive Health

Odisha State Board CHSE Odisha Class 12 Biology Solutions Chapter 4 Reproductive Health Textbook Questions and Answers.

CHSE Odisha 12th Class Biology Chapter 4 Question Answer Reproductive Health

Reproductive Health Class 12 Questions and Answers CHSE Odisha

Very Short Answer Type Questions

Multiple choice questions

Question 1.
The experimental plant material used by Mendel was
(a) cowpea
(b) garden pea
(c) wild pea
(d) sweet pea
Answer:
(b) garden pea

Question 2.
Which of the following characters is not among the seven characters considered by Mendel for his hybridisation experiments?
(a) Seed colour
(b) Pod shape
(c) Flower position
(d) Flower shape
Answer:
(d) Flower shape

Question 3.
Which law Mendel would not have proposed, if the phenomenon of linkage was known to him?
(a) Law of unit character
(b) Law of dominance
(c) Law of segregation
(d) Law of independent assortment
Answer:
(d) Law of independent assortment

Question 4.
The number of genotypes produced in F2-generation in Mendel’s monohybrid cross was
(a) 1
(b) 2
(c) 3
(d) 4
Answer:
(c) 3

Question 5.
In which of the crosses, half of the offsprings show dominant phenotype?
(a) Tt × Tt
(b) TT × tt
(c) Tt × tt
(d) TT × TT
Answer:
(c) Tt × tt

Question 6.
Two allelic genes are located on the
(a) same chromosome
(b) two homologous chromosomes
(c) two non-homologous chromosomes
(d) any two different chromosomes
Answer:
(b) two homologous chromosomes

Question 7.
Red (RR) Antirrhinum is crossed with white (rr) one. The F₁-hybrid is pink. This is an example of
(a) complete dominance
(b) codominance
(c) incomplete dominance
(d) complete recessive
Answer:
(c) incomplete dominance

Question 8.
In a dihybrid cross in F₂-generation, the parental types are far greater in number than the recombinants. This is due to
(a) linkage
(b) incomplete dominance
(c) multiple allelism
(d) complete dominance
Answer:
(a) linkage

Express in one or two word(s)

1. A pair of Mendelian factors (genes) that appear at a particular location on a particular chromosome and control the same characteristic.
Answer:
Alleles

2. Phenomenon where in the heterozygous condition an intermediate phenotype is observed.
Answer:
Incomplete dominance

3. The phenomenon of a single gene contributing to multiple phenotypic traits.
Answer:
Pleiotropy .

4. Genes which move together and do not show independent assortment.
Answer:
Linked gene

5. A cross between the F₁-hybrids with any one of the homozygous parents.
Answer:
Back cross

Correct the sentences, if required, by changing the underlined word (s) only

1. The process of transmission of characters through generations is known as variation.
Answer:
inheritance

2. In Mendel’s monohybrid cross, the dwarf phenotype is always homozygous.
Answer:
Correct statement

3. In Mendel’s dihybrid cross in F₂-generation, nine phenotypes are produced.
Answer:
four

4. The phenomenon of linkage disproved the principle of independent assortment.
Answer:
Correct statement

5. In a test cross, always dominant parent is used.
Answer:
recessive

6. The distance between genes in a constructed gene map is expressed as Mendel unit.
Answer:
Morgan

Fill in the blanks

1. Monohybrid cross in Regeneration yields ____ number of phenotypes.
Answer:
two

2. Monohybrid cross in Regeneration yields ____ number of genotypes.
Answer:
three

3. The name of scientist often coined with linkage is ____ .
Answer:
TH Morgan

4. Genotype of a plant showing the dominant phenotype can be determined by ____ cross.
Answer:
test

5. In a cross between AaBB and aaBB, the genotypic ratio in Ft-generation will be ____ .
Answer:
1 : 1

Short Answer Type Questions

Write notes on the following

Question 1.
Law of independent assortment
Answer:
It states that when two pairs of traits are combined in a hybrid, segregation of one pair of traits is independent to the other pair of traits. As in the dihybrid cross of Mendel the presence of new combinations, i.e. round-green and wrinkled-yellow suggests that the genes for shape of seed and colour of seed are assorted independently. The results (9:3:3:1), indicate that yellow and green seeds appear in the ratio of 9+3 : 3+1 = 3:1.
Similarly, the round and wrinkled seeds appear in the ratio of9 + 3:3+1 = 3:1.

This indicates that each of the two pairs of alternative characters viz yellow-green cotyledon colour is inherited independent of the round-wrinkled characters of the cotyledons. It means that at the time of gamete formation the factor for yellow colour enters the gametes ” independent of R or r, i.e. gene Y can be passed on to the gametes either with gene R or r.

Question 2.
Multiple alleles
Answer:
Multiple allelism and Inheritance of Blood Groups:
Each gene has alternative forms or allelomorphs. For example, the genes for rail and dwarf characters of pea plant arc ailcics or allelomorphs. Here, former is called normal or wild type and Iatcr as mutant type.
Sometimes, there may no be any aiternative form such mutation that results in complete elimination of a gene is known as null mutation. Sometimes silent mutation occurs in which mutation does not have any effect of all.

These mutations occur in wild gene in any direction with a possibility of formation of many alternative alleles. Some genes may occur in more than two allelic forms, i.e. a gene can mutate several times to produce several alternative expressions such genes are called multiple alleles.

Question 3.
Chromosomal basis of inheritance
Answer:
It was proposed independently by Walter Sutton and Theodore Boyen in 1902. They united the knowledge of chromosomal segregation with Mendelian principles and called it chromosornal theory of inheritance.
According to this theory

• All hereditary characters must be with sperms and egg cells as they provide bridge from one generation to the other.
• The hereditary factors must be carried by the nuclear material.
• Chromosomes are also found in pairs like the Mendelian alleles.
• The two alleles of a gene pair are located on homologous sites on the homologous chromosomes.

Question 4.
Codominance
Answer:
Codominance:
It is the phenomenon in which two alleles express themselves independently when present together in an organism. In other words, it is the phenomenon in which offspring shows resemblance to both the parents,
e.g. ABO blood grouping in humans.

Question 5.
Incomplete dominance
Answer:
Incomplete Dominance:
It is a phenomenon in which phenotype of the F₁-hybrid offsprings does not resemble any of the parent, but is an intermediate between the expression of two alleles in their homozygous state. Carl Correns was the one who reported incomplete dominance in plant Mirabilis jalapa. He showed the petal colour inheritance in this plant. Here, the phenotypic ratio deviates from Mendel’s monohybrid ratio but the parental characters reappear in F₂-generation.

Question 6.
Law of segregation
Answer:
This principle states that, though the parents contain two alleles during gamete formation, the factors or alleles of a pair segregate from each other, such that a gamete receives only one of the two factors. Hence, the alleles do not show any blending and both the characters are recovered as such in the F₂-generation though one of these is not seen in the F₁-generation.

Question 7.
Linkage
Answer:
The genes of a particular chromosome show the tendency to inherit together. This phenomenon of genic inheritance in which genes of a particular chromosome show their tendency to inherit together, i.e tendency to retain their parental combination even in the offsprings is known as linkage.

Question 8.
Recombination
Answer:
They attributed this due to physical association of the two genes and coined the term ‘linkage’ to describe this physical association of genes on a chromosome and the term ‘recombination’ to describe the generation of non-parental gene combinations. Morgan performed a test cross by crossing heterozygous grey-bodied and long-winged with homozygous recessive black-bodied and vestigial-winged fly

Question 9.
Test cross
Answer:
A special back cross to the recessive parent is known as test cross. This method was devised by Mendel to determine whether the dominant phenotype is homozygous or heterozygous.

For example, in a monohybrid cross between violet colour flower (W) and white colour flower (w), the F₁-hybrid was a violet colour flower. If all the F₁-progenies are of violet colour, then the dominant flower is homozygous and if the progenies are in 1:1 ratio, then the dominant flower is heterozygous.

Question 10.
Back cross
Answer:
Back cross is a cross of F₁ -progeny back to one of their parents. In back cross, there can be two possibilities, i.e. F₁ -hybrid to be crossed with homozygous dominant parent or with homozygous recessive parent.

Differentiate between the following

Question 1.
Homozygous and Heterozygous
Answer:
Differences between homozygous and heterozygous are as follows

Homozygous	Heterozygous
It is a condition when both alleles of a gene are similar.	It is a condition when both alleles of a gene are dissimilar.
The genotype is expressed as TT or tt.	The genotype expressed as Tt.
They are true breeding to purelines.	They are not true breeding.
The gametes produced by them are similar in genotype.	The gametes produced by them are of two types, one with dominant allele and other with recessive allele.

Question 2.
Genotype and Phenotype.
Differences between phenotype and genotype are as follows
Answer:

Phenotype	Genotype
It refers to observable traits or characters.	It refers to the genetic constitution of an individual.
It results from expression of genes.	It constitutes single gene pair or sum total of all the genes.
The phenotypic ratio of Mendel’s monohybrid cross is 3 : 1.	The genotypic ratio of Mendel’s monohybrid cross is 1:2:1.
It may change with age and environment.	It remains the same throughout the life of an individual.

Question 3.
Dominant genes and Recessive genes.
Answer:
Differences between dominant genes and recessive genes are as follows

Dominant genes	Recessive genes
When an allele expresses itself in the presence of its recessive allele, it is called dominant trait.	It can only express in the absence of its dominant allele and remain masked in its presence.
Dominant allele forms a complete functional enzyme due to which complete polyeptide is formed to express.	Recessive allele forms incomplete polypeptide enzyme due to which non-functionai polypetide is formed and fails to express completely.

Question 4.
Back cross and Test cross.
Answer:
Differences between back cross and test cross are as follows

Back cross	Test cross
It is a cross involving F1-progeny and either of the parents.	It is a cross involving
It is used by scientists to improve a breed or variety of plant or animal.	F1-individual and its recessive parent.

Question 5.
Qualitative inheritance and Quantitative inheritance.
Answer:
Differences between qualitative inheritance and quantitative inheritance are as follows

Qualitative inheritance	Quantitative inheritance
It deals with the inheritance of qualitative characters.	It deals with the inheritance of quantitative characters.
Each character is controlled by one pair of contrasting alleles.	Each character is controlled by more than one pair of non-allelic genes (Polygenes).
Each character has two distinct expressions, i.e. exhibits two distinct phenotypes.	Each character has an intergrading range of phenotypes.
The degree of expression remains the same whether the character is controlled by one or both the dominant genes.	The degree of expression depends on the number of the dominant genes.
Phenotypic expression is not affected by the environment.	Phenotypic expression is influenced by environmental factors.
Monogenic inheritance exhibits discontinuous pattern of inheritance.	Polygenic inheritance represents continuous pattern of inheritance.
F1-individuals resemble the dominant parent.	F1-individuals exhibit intermediate expression between the two parents.
F2-individuals exhibit 3:1 ratio. Intermediate expressions are not found.	In F2-generation, individuals with intermediate genotype and phenotype are maximum.
Examples of monogenic or qualitative inheritance are yellow or green coat color or round or wrinkled seed character in pea seeds.	Examples of polygenic or quantitative inheritance are height, weight, intelligence and skin color in human beings, milk yield in cattle and egg production in poultry.

Long Answer Type Questions

Question 1.
Give an account of Mendel’s monohybrid cross. What inference did Mendel draw from this experiment?
Answer:
Monohybrid Cross
The study of inheritance of a single pair of alleles or factors of a trait at a time (monohybrid cross) is called one gene inheritance. When a cross is made between pure tall and pure dwarf plant (for purity, the pureline is taken into consideration) in F₁-generation, all plants will be tall.

When F₁ -plants are self-pollinated, then in F₂-generation both tall and dwarf plants are found in approximate ratio of 3 : 1.

The dwarf plants of F₂ on self-pollination, produce dwarf plants generation after generation, while among tall plants, only 1 /3rd show this character generation after generation (pureline) and rest 2/3rd produce tall and dwarf in 3 : 1 ratio again (F₃ -generation).

Explanation Mendel’s monohybrid cross explained that in each main pair of alternative character one is expressed and other is masked.
The character which is expressed in F₁-generation is called dominant and the one which is not expressed is called recessive.

The monohybrid cross between tail and dwarf

In F₂-generation, the genotypic ratio is 1 : 2 : 1 and phenotypic ratio is 3 : 1. Mendel came to the conclusion that progeny possessing similar factors is called homozygous and the one which is hybrid is called heterozygous.

Mendel used english letters to record his observations of breeding experiments. He assigned capital letters for dominant characters and small letters for recessive characters which tabulated in the given below table

Characters	Dominant	Recessive
Seed shape	Round (R)	Wrinkled (r)
Seed colour	Yellow (Y)	Green (y)
Pod shape	Full (F)	Constricted (f)
Pod colour	Green (G)	Yellow (g)
Flower/Pod position	Axial (A)	Terminal (a)
Seed coat colour/Flower colour	Red/Violet (R/V)	White (r/v)
Plant height	Tall (T)	Dwarf (t)

Based on his observations on monohybrid crosses, Mendel proposed two general rules in order to consolidate his understanding of inheritance in monohybrid crosses.

Based on the Mendel’s observations, the German scientist Carl Correns formulated certain principles of heredity. These now known as Mendel’s laws of inheritance or the principles or laws of inheritance.
These are
Principle of Dominance:
It states that when two contrasting alleles for a character come together in an organism, only one is expressed completely and shows visible effect. This allele is called dominant and the other allele of the pair which does not express and remains hidden is called recessive.

For example, in the monohybrid cross when dwarf plant is crossed with tall plant, the Frgeneration are all tall plants. This shows that allele for tallness is dominant.

Question 2.
State and explain Mendel’s laws of inheritance.
Answer:
Following inferences were made by Mendel based on his observations
1. He proposed that some ‘factors’ passed down from parent to offsprings through the gametes over successive generations. Now-a-days, these factors are known as genes. Genes are hence, the units of inheritance. Genes which code for a pair of contrasting traits are known as alleles or allelomorphs, i.e. they are slightly different forms of the same gene.

2. Genes occur in pairs in which, one dominates the other called as the dominant factor or the gene which expresses itself, while the other remains hidden and is called recessive factor.

3. Allele can be similar in case of homozygous (TT or tt) and dissimilar in case of heterozygous (Tt).

4. In a true-breeding tall or dwarf pea variety, the allelic pair of genes for height are identical or homozygous.

5. TT and tt are called genotype (sum total of heredity or genetic make up) of the plant, while the term tall and dwarf are the phenotype.

6. When tall and dwarf plants produce gametes by process of meiosis, the alleles of the parental pair segregate and only one of the alleles gets transmitted to a gamete. Thus, there is only 50% chance of a gamete containing either allele, as the segregation is a random process.

7. During fertilisation, the two alleles, ‘T’ from one parent and V from other parent are united to produce a zygote, that has one ‘T’ and one allele or the hybrids have Tt.

8. Since, these hybrids contain alleles which express contrasting traits, the plants are heterozygous.

Question 3.
What do you mean by back cross and test cross? Explain test cross through an example.
Answer:
Back cross is a cross of F₁ -progeny back to one of their parents. In back cross, there can be two possibilities, i.e. F₁ -hybrid to be crossed with homozygous dominant parent or with homozygous recessive parent.

A special back cross to the recessive parent is known as test cross. This method was devised by Mendel to determine whether the dominant phenotype is homozygous or heterozygous.

For example, in a monohybrid cross between violet colour flower (W) and white colour flower (w), the F₁-hybrid was a violet colour flower. If all the F₁-progenies are of violet colour, then the dominant flower is homozygous and if the progenies are in 1:1 ratio, then the dominant flower is heterozygous.

Question 4.
Describe Mendel’s dihybrid cross.
Answer:
When two or more than two characters are taken in a cross it is called as polyhybrid cross, e.g. dihybrid cross, trihybrid cross, etc. A dihybrid cross is a cross involving two pairs of contrasting characters. For example, when a cross is made between yellow-round and wrinkled green seeds (both pureline homozygous), plants with only yellow round seeds are seen in F₁-generation but in F₁-generation, four types of combinations are observed.

Two of these combinations are similar to the parental combinations and others are new combinations. These are round green and wrinkled yellow.
The cross can be seen as shown in the figure

Phenotypic Ratio Round yellow : Round green : Wrinkled yellow : Wrinkled green = 9 : 3 : 3 : 1
Genotypic Ratio 1 : 2 :2 : 4 : 1 : 2 : 1 : 2 : 1

The ratio of four combinations in F₂-generation comes out to be 9 (round, yellow) : 3 (round, green) : 3 (wrinkled, yellow) : 1 (wrinkled, green). This ratio is called phenotypic dihybrid ratio. Phenotypic ratio of dihybrid test cross is 1 : 1 : 1 : 1.

Mendel’s Postulate Based on Dihybrid Cross:
Based on the result obtained from dihybrid crosses or two gene interaction, Mendel proposed the fourth postulate, i.e. law of independent assortment.

Question 5.
Give an account of linkage and recombination.
Answer:
Linkage, Crossing Over and Recombination:
According to ‘chromosomal theory of inheritance’, the chromosomes are vehicles of inheritance. Hence, the number of genes per individual for exceed the number of chromosomal pairs, i.e. each chromosome bears many genes. These genes are arranged in linear fashion over the chromosome and cannot show independent assortment.

In other words, we can say that the genes of a particular chromosome show the tendency to inherit together. This phenomenon of genic inheritance in which genes of a particular chromosome show their tendency to inherit together, i.e tendency to retain their parental combination even in the offsprings is known as linkage.

Morgan and his group observed in Drosophila that when the two genes in a dihybrid cross were situated on the same chromosome, the proportion of parental gene combinations were much higher than the non-parental type.

They attributed this due to physical association of the two genes and coined the term ‘linkage’ to describe this physical association of genes on a chromosome and the term ‘recombination’ to describe the generation of non-parental gene combinations. Morgan performed a test cross by crossing heterozygous grey-bodied and long-winged with homozygous recessive black-bodied and vestigial-winged fly. They obtained the following results

Phenotype	Per cent of occurrence
Grey body long wing	41.5
Black body vestigial wing	41.5
Grey body vestigial wing	8.5
Black body long wing	8.5

This result was not in accordance with Mendel’s law of inheritance. Now suppose in order to explain, we assume the alphabets G and g for grey and black body colours and L and 1 for long and vestigial wings, respectively.

Thus, linkage is a phenomenon of genic inheritance in which genes of a particular chromosome show their tendency to inherit together.
Morgan and his group also found that even when genes were grouped on the same chromosome, some genes were tightly linked, i.e. linkage is stronger between two genes, if the frequency of recombination is low (cross-A). Whereas, the frequency of recombination is higher, if genes are loosely linked, i.e. linkage is weak between two genes (cross-B) as given in figure


Linkage : Results of two dihybrid crosses conducted by Morgan. Cross ‘A’ shows crossing between genes y and w ; Cross ‘B’ shows crossing between genes w and m. Here, dominant wild type alleles are represented with (+) sign in superscript

Those traits present on same chromosome, which do not show any production of recombinants are completely linked which is known as complete linkage and it is very rare.

Linkage Groups:
All the genes linked together in a single chromosome constitute a linkage group. The number of linkage group in an organism is equal to their haploid number of chromosomes. This hypothesis was proved by TH Morgan by his experiments on Drosophila.

Morgan and his group hybridised yellow-bodied and white-eyed females with brown-bodied and red-eyed males (wild type) and intercrossed their F₁-progeny (cross A). It was observed that the two genes did not segregate independently of each other and the F₂-ratios deviated significantly from 9:3:3 :1 ratio.

In F₂-generation, parental combinations were 98.7% and the recombinants were 1.3%. In another cross (cross-B), between white-bodied female fly with miniature wing and a male fly with yellow body and normal wing, parental combinations were 62.8% and recombinants were 37.2% in F₂-generation. Thus, it was proved from the crosses that the linkage between genes for yellow body and white eyes is stronger than the linkage between the white body and miniature wing.

Chromosome Maps or Linkage Maps:
Alfred Sturtevant (Morgan’s student) used the frequency of recombination between gene pairs on the same chromosome as a measure of the .distance between genes and ‘mapped’ their position on the chromosome. Genetic maps are now used as a starting point in the sequencing of whole genomes as done in case of human genome sequencing project.

The frequency of recombination Cross Over Value (COV) is calculated by using the formula

A linkage or genetic chromosome map is a linear graphic representation of the sequence and relative distances of the various genes present in a chromosome. 1% crossing over between two linked genes is known as 1 map unit or Morgan (after TH Morgan, who is considered as ‘Father of Experimental Genetics’).