Trait B is more probable to arise early as this trait has already been existing and replicating in a larger percentage of the population as compared to trait A

Question - 2 : - How does the creation of variations in a species promote survival?

Answer - 2 : - Genetic variations enable the species to better adapt to changes in its environment. Moreover, it is an important force in evolution as it allows the frequency of alleles to increase or decrease through natural selection. These variations will determine the difference between extinction or continuation of the species.

Question - 3 : - How do Mendel’s experiments show that traits may be dominant or recessive?

Answer - 3 : - Mendel showed that the traits can either be dominant or recessive through his experiments that focused on mono-hybrid cross. The experiment involved him crossing tall (TT) pea plants with dwarf (tt) pea plants. The resultant plants which formed after fertilization represented the F1 (or filial) generation. All the F1 plants were tall. Mendel then proceeded to self-pollinate the filial generation plants and the result was that 1/4th of the plants obtained in the F2 generation were dwarfs. From this experiment, Mendel concluded that the F1 tall plants were not true-breeding, instead they carried the traits for both tall and dwarf heights. A portion of the plants were tall due to the fact that the traits for tallness were dominant over the traits for dwarfness. This cements the notion that traits can either be dominant or recessive.

Question - 4 : - How do Mendel’s experiments show that traits are inherited independently?

Answer - 4 : - Mendel’s experiments show that traits are inherited independently through his dihybrid cross experiment. The experiment involved him using two traits – namely, seed shape and seed colour. The colour yellow (YY) is dominant over green (yy), while the round shape (RR) is dominant over the wrinkled shape (rr). The F2 progeny of the dihybrid cross resulted in a phenotypic ratio of 9:3:3:1; therefore, 9 plants with round yellow (RRYY) seeds, 3 plants with round green (RRyy) seeds and 3 plants with wrinkled yellow (rrYY) seeds and one with wrinkled green seeds (rryy). He further observed that the wrinkled greens and the round yellow are parental combinations while the round green and wrinkled yellow are new. A dihybrid cross between two seeds with dominant traits (RRYY) and non-dominant traits (rryy) resulted in the production of 4 types of gametes (RY, Ry, rY and ry). This means each of the gametes segregate independently of the other; and each with a frequency of 25% of the total gametes produced.

Question - 5 : - A man with blood group A marries a woman with blood group O and their daughter has-

Answer - 5 : - blood group O. Is this information enough to tell you which of the traits – blood group A or O – is dominant? Why or why not?

Answer

Given information is not enough to tell us which characteristics are dominant –blood group A or O. Blood type A is always dominant in ABO blood and blood type O is always recessive. Here, the father’s blood group may be genotypically AA (homozygous) or AO (heterozygous), whereas that of mother can be OA or OO.

Question - 6 : - How is the sex of the child determined in human beings?

Answer - 6 : -

Sex of child in humans is determined by the males. Males have XX chromosomes while females have XY chromosomes. Hence, if:–

• The male’s X chromosomes combines with the female’s X chromosomes, the mother gives birth to a girl

• The male’s Y chromosome combines with the female’s X chromosome, the mother gives birth to a boy

Question - 7 : - What are the different ways in which individuals with a particular trait may increase in a population?

Answer - 7 : -

An individual attribute could increase in a population within the following 2 ways:-

(a) Natural selection: if an attribute is useful to a population, it’ll increase naturally.

For example – mosquitoes which are resilient against a particular pesticide will pass on its genes, so that future generations become resistant as well. The mosquitoes which are affected by the pesticide die out.

(b) Genetic drift: if a species faces a catastrophic event where most of the population is wiped out, the surviving population can pass on their traits to the following generations. This may result in a rise of the attribute within the population.

Question - 8 : - Why are traits acquired during the life-time of an individual not inherited?

Answer - 8 : - Traits acquired during a life-time cannot be inherited for successive generations as the changes do not reflect in the DNA of the germ cells. For instance, a football player cannot pass on his skills to his offspring as they are limited to non-reproductive cells only.

Question - 9 : - Why are the small numbers of surviving tigers a cause of worry from the point of view of genetics?

Answer - 9 : - As the size of the tiger population decreases, the genetic pool of the species decreases too. This results in a limitation on the variations which will be introduced within the genetic makeup of the tigers. This lack of variation will result in serious implications. For example, if an illness spreads within the tiger population, it can potentially wipe out the whole population, possibly causing their extinction.

Question - 10 : - What factors could lead to the rise of a new species?

Answer - 10 : -

Factors that would result in a new species are as follows:

(a) Mutation.

(b) Genetic drift.

(d) Geographical isolation.

(e) Generative isolation for prolonged periods

(f) Environmental factors on the isolated populations.

(g) Quantum of genetic variant transmissible from one generation to the following generation.

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Chapter 9 Heredity and Evolution Solutions

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