NCERT Exemplar Class 10 Science Solutions Chapter 9 Heredity and Evolution

Question:2

Two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny. The nature of the cross will be
(a) double fertilization
(b) self pollination
(c) cross fertilization
(d) no fertilization

Answer:(c)

Solution:
(a) double fertilization: one female gamete unites with two male gametes.
(b) self-pollination: the transfer of pollen from the anther of a flower to the stigma of the same flower
(c) cross-fertilization: fusion of male and female gametes from different individuals of the same species.
(d) no fertilization: Eggs fail to fertilize
In the question it is given that two pink coloured flowers on crossing resulted in 1 red, 2 pink and 1 white flower progeny By the above definitions, nature will be cross-fertilization.
Here fertilization of a plant using pollen from another plant of the same species is taking place. This is an example of cross-fertilization.
Therefore, option (c) is correct.

Question:3

A cross between a tall plant (TT) and short pea plant (tt) resulted in progeny that were all tall plants because
(a) tallness is the dominant trait
(b) shortness is the dominant trait
(c) tallness is the recessive trait
(d) height of pea plant is not governed by gene ‘T’ or ‘t’

Answer:(a)

Solution:
Tallness is a dominant trait even though there is only one allele of T in genotype but the output is tall.
Hence cross between a tall plant (TT) and short pea plant (tt) results in all tall plants.
The other trait, which is not shown is called the recessive trait.
Therefore, option (a) is correct.

Question:4

Which of the following statement is incorrect?
(a) For every hormone there is a gene.
(b) For every protein there is a gene.
(c) For production of every enzyme there is a gene.
(d) For every molecule of fat there is a gene

Answer: (d)
Solution:
Statements (a), (b), (c) are correct.
The incorrect statement is (d) as fat molecules are not related to genes. Fats are long-chain fatty acid.
Therefore, option (d) is the correct answer.

Question:5

If a round, green seeded pea plant (RR yy) is crossed with wrinkled, yellow seeded pea plant, (rr YY) the seeds produced in F1generation are
(a) round and yellow
(b) round and green
(c) wrinkled and green
(d) wrinkled and yellow

Answer: (a)
Solution:
The cross between RRyy and rrYY seeds will produce RrYy (round and yellow) seeds in F1 generation, because round and yellow are dominant traits.
Therefore, option (a) is correct.

Question:6

In human males all the chromosomes are paired perfectly exceptone. This/these unpaired chromosome is/are
(i) large chromosome
(ii) small chromosome
(iii) Y-chromosome
(iv) X-chromosome
(a) (i) and (ii) (b) (iii) only
(c) (iii) and (iv) (d) (ii) and (iv)

Answer: (c)
Solution:
Humans have two sex chromosomes, X and Y.
In females, two X chromosomes are present, making it a perfect pair.
But in males, one is a normal-sized X-chromosome while other is a short Y-chromosome.
Therefore, option (c) is correct.

Question:7

The maleness of a child is determined by
(a) the X chromosome in the zygote
(b) the Y chromosome in zygote
(c) the cytoplasm of germ cell which determines the sex
(d) sex is determined by chance

Answer: (b)
Solution:
The male outcome of a child is determined by the Y-chromosome in zygote inherited from the father.
If X-chromosome is inherited from the father, the zygote will develop into a female.
Therefore, option (b) is correct.

Question:8

A zygote which has an X-chromosome inherited from the fatherwill develop into a
(a) boy
(b) girl
(c) X- chromosome does not determine the sex of a child
(d) either boy or girl

Answer:(b)
Solution:
In humans, sex of the child is determined by chromosome inherited by the father.
If the zygote inherits X chromosome, the zygote will develop into a female.
If the zygote inherits Y chromosome, the zygote will develop into a male.
Therefore, option (b) is correct.

Question:9

Select the incorrect statement
(a) Frequency of certain genes in a population change over several generations resulting in
evolution
(b) Reduction in weight of the organism due to starvation is genetically controlled
(c) Low weight parents can have heavy weight progeny
(d) Traits which are not inherited over generations do not cause evolution

Answer: (b)
Solution:
(a) The change in the heritable characteristics of biological populations over successive generations is called Evolution. So frequency of certain genes in a population change over several generations resulting in evolution. Hence the statement is correct.
(b) Low weight is not a trait that is genetically controlled or inherited. So, the weight reduction due to starvation will not change the DNA of the germ cells. Hence the statement is incorrect.
(c) As discussed in option (b), Low weight is not a trait that is genetically controlled or inherited. Hence, low weight parents may have heavy weight progeny. Hence the statement is correct.
(d) The change in the heritable characteristics of biological populations over successive generations is called Evolution. Traits which are not inherited, i.e., the acquired traits are simply changes in non-reproductive tissues, so, cannot be passed on to DNA of germ cells. Hence the statement is correct.
Therefore, option (b) is correct.

Question:10

New species may be formed if
(i) DNA undergoes significant changes in germ cells
(ii) chromosome number changes in the gamete
(iii) there is no change in the genetic material
(iv) mating does not take place
(a) (i) and (ii)
(b) (i) and (iii)
(c) (ii), (iii) and (iv)
(d) (i), (ii) and (iii)

Answer: (a)
Solution:
(i) If DNA undergoes a significant change in germ cells, new species may be formed. These changes in DNA will be inherited by the germ cells, which passes to the next generation and will be inherited by the subsequent generations.
(ii) chromosome number changes in the gamete lead to a change in the gene pool and causes variation.
(iii) If there is no change in the genetic material, new species will not be formed.
(iv) If mating does not take place, new species will not be formed
Therefore, option (a) is correct.

Question:11

Two pea plants one with round green seeds (RRyy) and another with wrinkled yellow (rrYY) seeds produce F1progeny that haveround, yellow (RrYy) seeds. When F1plants are selfed, the F2progeny will have new combination of characters. Choose the newcombination from the following
(i) Round, yellow
(ii) Round, green
(iii) Wrinkled, yellow
(iv) Wrinkled, green
(a) (i) and (ii)
(b) (i) and (iv)
(c) (ii) and (iii)
(d) (i) and (iii)

Answer: (b)
Solution:
Here a typical dihybrid cross is given.
Two characters are considered at a time:

1. Colour of the seeds (green or yellow)
2. Shape of the seeds (round or wrinkled).

When F1 plants are selfed in a typical dihybrid cross, we get two parental combinations in the ratio 9:3:3:1.
So the phenotypic ratio of 9: 3: 3: 1 is obtained.
Round Yellow: Round green: Wrinkled yellow: Wrinkled green = 9:3:3: 1 The two new combinations are round & yellow seeds and wrinkled & green seeds are
Therefore, option (b) is correct.

Question:12

A basket of vegetables contains carrot, potato, radish and tomato. Which of them represent the correct homologous structures?
(a) Carrot and potato
(b) Carrot and tomato
(c) Radish and carrot
(d) Radish and potato

Answer:(c)
Solution:
The structures that are similar in related organisms because they were inherited from a common ancestor are Homologous structures. These may or may not have the same function as in the descendants.
Radish and carrot represent homologous structures as they have the same structure (or basic design) though they are different species. Both store energy and have modified roots.
Therefore, option (c) is correct.

Question:13

Select the correct statement
(a) Tendril of a pea plant and phylloclade of Opuntia are homologous
(b) Tendril of a pea plant and phylloclade of Opuntia are analogous
(c) Wings of birds and limbs of lizards are analogous
(d) Wings of birds and wings of bat are homologous

Answer: (a)
Solution:
The structures that are similar in related organisms because they were inherited from a common ancestor are Homologous structures. These may or may not have the same function as in the descendants.
(a) Tendril of a pea plant and phylloclade of Opuntia both structures belong to the shoot system and are inherited from a common ancestor. Phylloclade of Opuntia is modified for photosynthesis and tendril is meant to provide support to the weak stem. Hence these are homologous.
(b) Analogous structures are similar structures that evolved independently into two living organisms for the same purpose. Tendril of a pea plant and phylloclade of Opuntia are homologous as discussed in part (a).
(c) Analogous structures are similar structures that evolved independently into two living organisms for the same purpose. Wings of birds and limbs of lizards do not have the same purpose hence these are not analogous.
(d) Bat wings consist of flaps of skin stretched between the bones of the fingers and arm. Bird wings consist of feathers extending all along the arm. These structural dissimilarities suggest that bird wings and bat wings were not inherited from a common ancestor with wings. Hence these are not homologous.
Therefore, option (a) is correct.

Question:14

If the fossil of an organism is found in the deeper layers of earth, then we can predict that
(a) the extinction of organism has occurred recently
(b) the extinction of organism has occurred thousands of years ago
(c) the fossil position in the layers of earth is not related to its time of extinction
(d) time of extinction cannot be determined

Answer: (b)
Solution:
A fossil is any preserved remains, impression, or trace of any once-living thing from a past geological age.
If the fossil of an organism is found in the deeper layers of earth, then the extinction of an organism is predicted to have occurred thousands of years ago.
The more recent fossils are the ones found closer to the surface.
Therefore, option (b) is correct.

Question:15

Which of the following statements is not true with respect to variation?
(a) All variations in a species have equal chance of survival
(b) Change in genetic composition results in variation
(c) Selection of variants by environmental factors forms the basis of evolutionary processes.
(d) Variation is minimum in asexual reproduction

Answer: (a)
Solution:
(a) All variations in a species have equal chance of survival: the statement is incorrect. Some variations are too drastic that the new DNA cannot work with it, such as, death of a newborn cell.
(b) Change in genetic composition results in variation: True
(c) Selection of variants by environmental factors forms the basis of evolutionary processes: True
(d) Variation is minimum in asexual reproduction: True
Therefore, option (a) is correct.

Question:16

A trait in an organism is influenced by
(a) paternal DNA only
(b) maternal DNA only
(c) both maternal and paternal DNA
(d) neither by paternal nor by maternal DNA

Answer:(c)
Solution:
Both maternal and paternal DNA influences the traits of an organism.
Both mother and father pass their genes to their children during sexual reproduction, which determines their traits.
Traits or characteristic features, are passed down from one generation to another through genes found on the chromosomes.
Therefore, option (c) is correct.

Question:17

Select the group which shares maximum number of common characters
(a) two individuals of a species
(b) two species of a genus
(c) two genera of a family
(d) two genera of two families

Answer: (a)
Solution:
Taxonomic Hierarchy:

• Kingdom
• Phylum
• Class
• Order
• Family
• Genus
• Species

Common characters increase as we move from higher taxonomic rank to lower one. As per the order mentioned above, among species, genus, family; species is the lowest taxonomic rank.
Hence, two individuals of the same species will share maximum number of common characters.
Therefore, option (a) is correct.

Question:18

According to the evolutionary theory, formation of a new species is generally due to
(a) sudden creation by nature
(b) accumulation of variations over several generations
(c) clones formed during asexual reproduction
(d) movement of individuals from one habitat to another

Answer: (b)
Solution:
The change in the heritable characteristics of biological populations over successive generations is called Evolution.
(a) Sudden creation by nature is not an evolutionary process
(b) Accumulation of variations over several generations forming new species is an evolutionary process. Genetic drift accumulates different changes in sub-populations of a species. In the different geographic locations, natural selection may also operate differently. Eventually, different groups of new species will be formed.
(c) Cloning is the process of producing individuals with identical or virtually identical DNA, either naturally or artificially. It is not an evolutionary process.
(d) Movement of individuals from one habitat to another is not evolution
Therefore, option (b) is correct.

Question:19

From the list given below, select the character which can be acquired but not inherited
(a) colour of eye
(b) colour of skin
(c) size of body
(d) nature of hair

Answer: (c)
Solution:

• Inherited traits: are present in the person since the time of his birth and are passed on from one generation to another
• Acquired traits: A person develops during his lifetime. Acquired traits develop in response to the environment.
• Colour of eye, colour of skin and nature of hair cannot be developed during our lifetime. So these are considered as inherited.
• The size of the body is an acquired trait because it can be changed on the availability of less or more food.

Therefore, option (c) is correct.

Question:20

The two versions of a trait (character) which are brought in by the male and female gametes are situated on
(a) copies of the same chromosome
(b) two different chromosomes
(c) sex chromosomes
(d) any chromosome

Answer: (a)
Solution:
The genes are available in various structures or alleles in a sexually reproducing population. These alleles are situated on various copies of the same chromosomes. In an ordinarily diploid sexually reproducing population like humans, every individual has 23 sets of chromosomes. Subsequently, there are two copies of each chromosome.
One chromosome comes from the father through the male gamete and the other chromosome comes from the mother through the female gamete. After fertilization, the zygote is produced having 23 pairs of chromosomes.
Hence, the two versions of a trait are situated on copies of the same chromosome.
Therefore, option (a) is correct.

Question:21

Select the statements that describe characteristics of genes
(i) genes are a specific sequence of bases in a DNA molecule
(ii) a gene does not code for proteins
(iii) in individuals of a given species, a specific gene is located on a particular chromosome
(iv) each chromosome has only one gene
(a) (i) and (ii)
(b) (i) and (iii)
(c) (i) and (iv)
(d) (ii) and (iv)

Answer: (b)
Solution:
Genes are stretches of DNA found on chromosomes of a cell. A gene contains information for making proteins in a cell. A specific gene is located on a particular chromosome in individuals of a given species.
Therefore, option (b) is correct.

Question:22

In peas, a pure tall plant (TT) is crossed with a short plant (tt). The ratio of pure tall plants to short plants in F₂ is
(a) 1 : 3
(b) 3 : 1
(c) 1 : 1
(d) 2 : 1

Answer: (d)
Solution:
Parent generation TT (pure tall) x tt (pure dwarf)
Gametes T t
F₁ generation Tt (heterozygous tall)
F₂ generation

F₂ Generation Phenotypic ratio = 3:1
Genotypic ratio = 1: 2: 1
Therefore, option (d) is correct.

Question:23

The number of pair (s) of sex chromosomes in the zygote of humans is
(a) one (b) two
(c) three (d) four

Answer:(a)
Solution:
The number of sex chromosomes in the zygote of humans is one pair. It is not always a perfect pair. In females, it is perfect with two X-chromosomes. However, in males, there is one X-chromosome and one Y-chromosome.
Therefore, option (a) is correct.

Question:24

The theory of evolution of species by natural selection was given by
(a) Mendel (b) Darwin
(c) Morgan (d) Lamarck

Answer: (b)
Solution:
The theory of evolution of species by natural selection was given by Charles Darwin.
Mendel gave the laws of inheritance of traits. Morgan worked on Drosophila melanogaster and gave concept of linked genes, Lamarck gave the theory of inheritance of acquired characteristics
Therefore, option (b) is correct.

Question:25

Some dinosaurs had feathers although they could not fly but birds have feathers that help them to fly. In the context of evolution thismeans that
(a) reptiles have evolved from birds
(b) there is no evolutionary connection between reptiles and birds
(c) feathers are homologous structures in both the organisms
(d) birds have evolved from reptiles

Answer: (d)
Solution:
In the context of evolution, the use of feathers by birds for flying means that birds have evolved from reptiles. Dinosaurs had feathers but could not fly using them. Birds later adapted the feathers for flight. Since dinosaurs were reptiles, this means that birds have evolved from them.
Therefore, option (d) is correct.

Question:27

Do genetic combination of mothers play a significant role in determining the sex of a new born.

Answer:

Mothers have a pair of X-chromosomes. So they do not play significant role in determining the sex of a new born.
Humans have two sex chromosomes, X and Y.
In females, two X chromosomes are present, making it a perfect pair.
But in males, one is a normal-sized X-chromosome while other is a short Y-chromosome.
In humans, sex of the child is determined by chromosome inherited by the father.
If the zygote inherits X chromosome, the zygote will develop into a female.
If the zygote inherits Y chromosome, the zygote will develop into a male.
All children will inherit an X-chromosome from their mother regardless whether they are boys or girls

Question:28

Mention three important features of fossils which help in the study of evolution.

Answer:

Important features of fossils which help in the study of evolution are
(i) Mode of preservation of ancient species is represented by Fossils.
(ii) Relationship between organisms and their ancestors is established using fossils.
(iii) Fossils help in establishing the time period in which organisms lived.

Heredity and Evolution Excercise: 3.5

Question:29

Why do all the gametes formed in human females have an X chromosome?

Answer:

Human females have two X-chromosomes called sex chromosome. During meiosis at the time of gamete formation, one X-chromosome enters each gamete. Hence, all the gametes formed in human females possess an X-chromosome.

Question:30

In human beings, the statistical probability of getting either a male or female child is 50 : 50. Give a suitable explanation.

Answer:

• Humans have two sex chromosomes, X and Y.
• In females, two X chromosomes are present, making it a perfect pair.
• But in males, one is a normal-sized X-chromosome while other is a short Y-chromosome.
• In humans, sex of the child is determined by chromosome inherited by the father.
• If the zygote inherits X chromosome, the zygote will develop into a female.
• If the zygote inherits Y chromosome, the zygote will develop into a male.

So, the sex of an infant is determined by the type of sex chromosome contributed by the male gamete. A male produces two types of sperms-one type bears 22 + X composition and the other, 22 + Y. Therefore, a male has 50% sperms with X-chromosomes and other 50% with Y-chromosome.
So the zygote receives X chromosome from the female but from male zygote can receive either X or Y chromosome which is 50 – 50 probability wise.

Question:31

A very small population of a species faces a greater threat of extinction than a larger population. Provide a suitable genetic explanation.

Answer:

A very small population of a species faces a greater threat of extinction than a larger population because of the following reasons:
1. Small population promotes inbreeding.
Production of offspring from the mating or breeding of individuals or organisms that are closely related genetically, is
known as inbreeding.
2. Small population is helpless against abrupt change in climate. Because of genetic drift, odds of species with small
population may wipe out.
3. Small population gets reproductively isolated so no exchange of genes, that would lead to less variations.

Question:32

What are homologous structures? Give an example. Is it necessary that homologous structures always have a common ancestor?

Answer:

The structures that are similar in related organisms because they were inherited from a common ancestor are Homologous structures. These may or may not have the same function as in the descendants.
Examples: forelimbs of reptiles, amphibians, birds and mammals.
Yes, homologous structures are inherited from a common ancestor.
For example,

1. Tendril of a pea plant and phylloclade of Opuntia both the structures belong to the shoot system and are inherited from a common ancestor. Phylloclade of Opuntia is modified for photosynthesis and tendril is meant to provide support to the weak stem. Hence these are homologous.
2. The mammals as well as birds, reptiles and amphibians all have four limbs. The basic structure of limbs is similar though it has been modified to perform different functions in various vertebrates. Thus, they have evolved from a common ancestor
   

Question:33

Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.

Answer:

Common ancestry may extraordinarily restrict the degree of diversity, e.g., all birds are closely related, they have common ancestors but birds and reptiles are also related.
Animals show immense variety in their structures, they probably have diverse ancestry. If we arrange species according to the evolutionary relationship, we can develop small groups of living beings with ongoing regular predecessors. These are additionally named as super-groups with the most distinct common ancestors. Moreover, we can continue to go in reverse in this arrangement to go to a single species at the earliest reference point of evolutionary time. But having a single ancestor would restrict the diversity seen in the organisms today.
Along these lines, it very well may be said that the occurrence of animals on Earth proposes their diverse ancestry too.

Question:34

Give the pair of contrasting traits of the following characters in pea plant and mention which is dominant and recessive (i) yellow seed (ii) round seed

Answer:

Character Contrasting traits
Dominant Recessive
(i) seed color - yellow green
(ii) seed shape- round wrinkled

Question:35

Why did Mendel choose pea plant for his experiments?

Answer:

Mendel choose pea plant for his experiment for the following reasons

1. Easy to cultivate
2. They have short life span
3. They have sharply defined and contrasting traits (For example, height (tall, dwarf), seed color (yellow-green), etc.)
4. These are self-pollinated.
5. They have bisexual characteristics
6. These have excellent disease resistance
7. Have an optimal rate of survival

Question:36

A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.

Answer:

Humans have two sex chromosomes, X and Y.
In females, two X chromosomes are present, making it a perfect pair.
But in males, one is a normal-sized X-chromosome while other is a short Y-chromosome.
In humans, sex of the child is determined by chromosome inherited by the father.
If the zygote inherits X chromosome, the zygote will develop into a female.
If the zygote inherits Y chromosome, the zygote will develop into a male.
So, the sex of an infant is determined by the type of sex chromosome contributed by the male gamete.
If a woman has only daughters, this is because the child will have XX pair of sex chromosome.
This indicates that in every fusion, the sperm carrying X-chromosome fertilized the ovum

Question:38

Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved thanbacteria? Provide a suitable explanation.

Answer:

Evolution is basically the generation of diversity and the moulding of diversity by ecological selections. Additionally, it isn't as though the recently created species are in any capacity better than the older ones.
It is only that common choice and hereditary drift have together prompted the arrangement of a population that cannot reproduce with the first one.
The only reformist pattern in evolution is that more and more complex body designs have arisen over time. Nonetheless, once more, it isn't as though the more established plans are inefficient. In fact, one of the least complex living things—bacteria— possess the most inhospitable natural surroundings like hot springs, deep-sea thermal vents and the ice in Antarctica. In other words, human beings are not the peak of development, rather just one more animal varieties in the plentiful range of advancing life.

Question:39

All the human races like Africans, Asians, Europeans, Americans and others might have evolved from a common ancestor. Provide a few evidences in support of this view.

Answer:

Irrespective of their races, all humans are a single species. We can notice features like:

1. A common body plan, structure, physiology and metabolism.
2. A constant chromosome number, i.e., 46.
3. Genetic makeup is also similar, almost 99.9% DNA is same in all humans.
4. Can freely inter-breed to produce off-springs.

Evolutionary events indicate the origin of humans from a common African ancestor. Homo sapiens (earliest members of the human species) can be traced there. On the basis of above information, we can conclude that all human races seem to have common ancestor.

Question:40

Differentiate between inherited and acquired characters. Give one example for each type.

Answer:

Differences between inherited and acquired characters

Question:41

Give reasons why acquired characters are not inherited.

Answer:

Acquired characters are traits that are not inherited, i.e., the acquired traits are simply changes in non-reproductive tissues, so, cannot be passed on to DNA of germ cells.
Hence, acquired characters do not produce a change in the genes of germ cells, so they cannot be inherited.
Example: The skills like cycling do not have any genetic changes in the individual who knows it. So it cannot pass from one generation to another as genetic code is the only way organisms pass information to the next generation.

Question:42

Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.

Answer:

Morphological structures are effortlessly visible to us. As the name suggests, molecular structures are the ones at sub-atomic level. Different biomolecules are needed to make an organism. Diversity in morphological structure causes diversity in organisms that we see around us. Life started as simple forms and bit by bit it developed into numerous unpredictable organisms. In this manner, it tends to be said that morphological structures show the least stability. When we look at the molecular level, all the life forms are comprised of same biomolecules. DNA, protein, lipid, carbohydrates, etc. are available in all creatures. The structure of DNA is same in each life form, however the quantity of DNAs shifts starting with one organism then onto the next.
Regardless of the sort of organism, a DNA molecule or a protein molecule would have the same structure. Consequently, it can be said that molecular structures show incredible stability.

Question:43

In the following crosses write the characteristics of the progeny
Cross Progeny
(a) RRYY x RRYY
Round, yellow Round, yellow ________
(b) RrYy x Rr Yy
Round, yellow Round, yellow ________
(c) rryy x rryy
wrinkled, green wrinkled, green _______
(d) RRYY x rryy
Round, yellow wrinkled, green ________

Answer:

(a) Parents: RRYY x RRYY
Gametes: RY x RY
Progeny: All are RRYY (Round Yellow)
(b) Parents: RrYy x RrYy
Gametes: RY; Ry; rY; ry RY; Ry; rY; ry
Progeny: Round yellow, Round green, Wrinkled yellow, Wrinkled, green
(c) Parents: rryy x rryy
Gametes: ry ry
Progeny: rryy
All of the progeny is going to be wrinkled green
(d) Parents: RRYY x rryy
Gametes: RY ry
Progeny: RrYy
All of the progeny is going to be round yellow

Question:44

Study the following cross and showing self pollination in F1, fill in the blank and answer the question that follows
Parents: RRYY × rryy
Round, Yellow wrinkled. green
F1: RrYy × ?
Round, yellow ?

Answer:

Self-cross in F1 shows dominant character (law of dominance) in F1 generation.
Answer will be: Rr Yy
Round, yellow

Question:45

In question 44, what are the combinations of character in the F2progeny? What are their ratios?

Answer:

RrYy x RrYy
Gametes : RY ; Ry ; ry ; ry
Gametes : RY ; Ry ; ry ; ry

Progeny Ratio: Round Yellow : Round green : wrinkled Yellow : wrinkled green
9 : 3 : 3 : 1

Question:46

Give the basic features of the mechanism of inheritance.

Answer:

Features of mechanism of inheritance are following:
(i) Genes control characters.
(ii) Genes are found on chromosomes
(iii) Genes may be of two or more forms. One form may be dominant while other is recessive.
(iv) Each parent has a couple of genes for each characteristic on a chromosome.
(v) Zygote carries characteristics of both the parents which are inherited through the genes. Zygote is formed when a male gamete fuses with the female gamete during fertilization. Zygote has full set of genes. This gives variation from one generation to next generation.
(vi) The off-springs inherit two genes (or a pair of genes) for each trait from its parent’s characters.

Question:47

Give reasons for the appearance of new combinations of characters in the F2progeny.

Answer:

Law of independent assortment: This is the reason for the appearance of new combinations in the F2 generation. It states that:
When two pairs of traits are combined in a hybrid, one pair of character segregates independent of the other pair of character.
It indicates that the chances for the pea seeds to be round or wrinkled do not depend on their chances to be yellow or green.
Each pair of alleles is independent of the other pairs.
In a dihybrid cross between two plants having round yellow (RRYY) and wrinkled green seeds (rryy), four types of gametes are produced (RY, Ry, rY, ry). Each of these segregate independent of each other.

Progeny Ratio: Round Yellow: Round green: wrinkled Yellow: wrinkled green
9 : 3 : 3: 1