Short Answer Type Questions
Q 1. Do genetic combination of mothers play a significant role in determining the sex of new born?
Ans: No, mothers have no role in determining the sex of the new born. Mothers have a pair of X chromosome and all children will inherit an ‘X’ chromosome from their mother regardless of whether they are boys or girls. Only presence or absence of y chromosome present in males gamete determine the sex of new born.
Q 2. Mention three important features of fossils which help in the study of evolution.
Ans: The three important features of fossils that help in the study of evolution are as follows:
(i) It helps in establishing the time period in which the organisms lived.
(ii) It helps in establishing evolutionary traits among organisms and their ancestors.
(iii) It is the mode of preservation of ancient species.
Q 3. Why do all the gametes formed in human females have an X-chromosome?
Ans: All the gametes formed in human females have an ‘X’ chromosome because during meiosis at the time of gamete formation, one X chromosome enters each gamete.
Q4. In human beings, the statistical probability of getting either a male or female child is 50: 50. Give a suitable explanation.
Ans: The sex of a child is determined by the type of sex chromosome contributed by male gamete. The statistical probability of getting either a male or female child is 50 : 50, because the ratio of male gametes containing X chromsome and those containing Y chromosome is 50 : 50.
Q 5. A very small population of a species faces a greater threat of extinction than a larger population, Provide a suitable genetic explanation.
Ans: A small population of a species impose extensive inbreeding among them, which limits the appearance of variations and put the species at a disadvantage. Also they fail to cope up with the environmental changes, thus become extinct.
Q 6. Evolution has exhibited a greater stability of molecular structure when compared with morphological structures. Comment on the statement and justify your opinion.
Ans: There is immense diversity in size, form, structure and morphological features in the living world. At the molecular level these diverse types of organisms exhibit similarity of the basic biomolecules like DNA, RNA, carbohydrates, proteins, etc.
Evolution is not related to complexity of body, therefore, it is difficult to ray that complex organisms are more evolved than the simpler organisms.
Q 7. Does the occurrence of diversity of animals on earth suggest their diverse ancestry also? Discuss this point in the light of evolution.
Ans: Diversity of animals does not mean that they have diverse ancestry because common ancestry greatly limit the extent of diversity. If the animals are inhabiting in the same habitat their evolution by speciation and geographical isolation is also not likely. Animals having a common ancestor have developed new traits forming various groups of animals.
Q 8. 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
Ans: (i) Seed colour → Yellow (dominant), green (recessive)
Seed shape → Round (dominant), wrinkled (recessive)
Q 9. A woman has only daughters. Analyse the situation genetically and provide a suitable explanation.
Ans: The women produces ova with ‘X’ chromosome and man produces sperms with X and Y chromosome. If the husband of the woman transfer X chromosome, then child will be a girl. On the other hand, if the husband transfer Y chromosome, the child will be a boy. In the case, the husband is always transferring X chromosome and hence, all the children are girl.
Q 10. Give reasons why acquired characters are not inherited.
Ans: Acquired characters are not inherited because they do not produce change in the DNA of germ cells, only those characters which have a gene for them can be inherited.
Long Answer Type Questions
Q. 11. In the following crosses write the characteristics of the progeny:
Ans: (a) Round yellow
(b) Round yellow, Round green Wrinkled yellow, Wrinkled green
(c) Wrinkled green
(d) Round yellow
Q 12. Study the following cross and showing self-pollination in F1, fill in the blank and answer the question that follows:
Ans: Rr Yy Round, yellow.
Q 13. In previous question, what are the combinations of character in the F2 progeny? What are their ratios?
Ans: Round yellow - 9 ; Round green - 3
Wrinkled yellow - 3 ; Wrinkled green - 1
i.e.9: 3:3 :1.
Q 14. Give reasons for the appearance of new combinations of characters in the F2 progeny.
Ans: An organism can inherit each character independently. So, in the F2 progeny new combination of character appears. Tall/Short and Round/Wrinkled seed trait are independently inherited.
Q 15. Does geographical isolation of individual of a species lead to formation of a new species? Provide a suitable explanation.
Ans: Yes, geographical isolation of individual of a species lead to the formation of a new species. Geographical isolation of a population leads to genetic drift and there will be no gene flow between it and the parent species. Inbreeding in small population will reproduce among themselves and generate new variations. Accumulation of those variations over several generations will lead to formation of new species.
Q 16. Bacteria have a simpler body plan when compared with human beings. Does it mean that human beings are more evolved than bacteria? Provide a suitable explanation.
Ans: No, it does not mean that human beings are more evolved than bacteria. Both bacteria and human beings perform all activities of life to live in their environment. Human beings have more complex organisation and differentiation which are absent in bacteria. However, bacteria can survive in extreme conditions and inhospitable places such as hot springs, deep-sea thermal rents, craters of volcanoes, in the ice of Antartica, etc. in which human can not.
Q 17. All the human races like Africans, Asians, Europeans, Americans and other might have evolved from a common ancestor. Provide a few evidences in support of this view.
Ans: All the human races have evolved from a common ancestor because they possess:
(i) common body plan
(ii) common structure
(iii) common physiology
(iv) common metabolism
(v) constant chromosome number
(vi) common genetic blue-print
(vii) free inter-breeding
Q 18. Give the basic features of the mechanism of inheritance.
Ans: Basic features for the mechanism of Inheritance are as follows:
(i) Characters are controlled by genes.
(ii) Each gene controls one character.
(iii) Genes are located on chromosomes.
(iv) There may be two or more forms of gene.
(v) An individual possess two forms of genes whether similar or dissimilar.
(vi) One form may be dominant over the other.
(vii) The two alleles separate at the time of gamete formation.
(viii) The two forms are brought together in the zygote.
(ix) Alleles of different genes located on separate chromosomes behave independent of one another.