Heredity - Evolution — Practice

Question 1

Palaeontologists deal with

Accepted Answer

Fossil evidences

Question 2

Natural selection means

Accepted Answer

Nature selects desirable characters and rejects undesirable ones

Question 3

Humans have ______ pairs of autosomes and ______ pair of sex chromosomes; the study of fossils is ______; and the forelimb of a whale is for swimming whereas in a horse it is used for ______.

Accepted Answer

22 pairs of autosomes and 1 pair of allosomes; palaeontology; running

Question 4

In a pea plant, if we cross-pollinate a pure purple-flowered plant with a pure white-flowered one, what percentage of the F2 generation will show the recessive trait, and what does Mendel's Table 4 record for this character?

Accepted Answer

About 25 per cent; Mendel counted 705 purple to 224 white, a ratio of 3.15 : 1.

Question 5

A researcher wants to cross a pure tall plant (TT) with a pure dwarf plant (tt). What would the F1 and F2 generations be?

Accepted Answer

F1 is entirely Tt and all tall. F2 gives 1 TT : 2 Tt : 1 tt, which appears as three tall plants to one dwarf.

Question 6

An experimenter cut the tails of parent rats. Will the daughter rats have tails? Explain your argument.

Accepted Answer

Yes. Cutting a tail is a change to non-reproductive tissue and does not alter the DNA of the germ cells, so it cannot be inherited.

Question 7

Write a brief note on analogous organs, and say how they differ from homologous organs.

Accepted Answer

Analogous organs are structurally different but functionally similar, arising by convergent evolution; homologous organs are structurally similar but functionally different, arising by divergent evolution from a common ancestor.

Question 8

In a mango garden a farmer sees one tree heavy with fruit but full of pests, and another pest-free but with few mangoes. He wants a tree that is both heavy-bearing and pest free. Is it possible, and how?

Accepted Answer

Yes, by grafting: joining the rooted stock of the pest-resistant tree to a scion taken from the heavy-bearing tree, so the new plant carries both desirable characters.

Question 9

Explain Darwin's theory of natural selection with an example.

Accepted Answer

Populations vary, offspring are over-produced, the struggle for existence eliminates the less fit, and the useful variations accumulate until they become common — as with the green beetles that crows could not see against green leaves.

Question 10

Draw a checker board for a dihybrid cross between YYRR and yyrr and explain the resulting ratio.

Accepted Answer

F1 is all YyRr, yellow and round. Each F1 plant makes four gamete types — RY, Ry, rY, ry — and the 4 by 4 board gives 9 round yellow, 3 round green, 3 wrinkled yellow and 1 wrinkled green.

Practice — Heredity - Evolution

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