Heredity and Evolution — Questions & Answers

Sample questions from Heredity and Evolution

1. Q1. In the second generation of Mendel tall and short cross, the ratio of tall to short plants was about:

   • A.1 to 1
   • B.9 to 3
   • C.1 to 3
   • D.3 to 1✓
   Solution

   D is correct: a cross between two plants of the first generation gives tall and short in the ratio three to one, because three of the four combinations hold at least one dominant factor. A is the ratio in a test cross with the recessive parent. B is part of a ratio from a cross following two characters. C reverses the correct answer.

2. Q2. Germ cells have half the number of chromosomes of a body cell so that:

   • A.They can move faster
   • B.They use less energy
   • C.The zygote formed by their fusion has the full number, and it is not doubled in each generation✓
   • D.They can divide more often
   Solution

   C is correct: if each germ cell carried the full set, the number would double at every fertilisation, so the number is halved during their formation and the original number is restored at fusion. A is not a reason connected with inheritance. B and D are not consequences of the chromosome number.

3. Q3. Artificial selection, as in the making of cabbage, cauliflower and broccoli from a single wild plant, shows that:

   • A.Selection acting over many generations can produce very different forms from one original stock✓
   • B.Man can create new genes at will
   • C.Evolution does not happen in nature
   • D.Wild cabbage was already cauliflower
   Solution

   A is correct: by choosing plants with the largest leaves, the tightest flower cluster or the swollen stem, generation after generation, farmers produced forms that hardly resemble one another, which is a visible model of what natural selection does over longer periods. B is false, since the farmer selects among existing variations rather than creating them. C is the reverse of the lesson. D denies the history.

4. Q4. Case 20: A new species forms when populations can no longer:

   • A.interbreed to produce fertile offspring✓
   • B.eat the same food
   • C.live in the same climate only
   • D.have any DNA
   Solution

   Reproductive isolation is a key criterion for separate species.

5. Q5. The ratio obtained in the second generation of a dihybrid cross is:

   • A.9 to 3 to 3 to 1✓
   • B.3 to 1
   • C.1 to 1 to 1 to 1
   • D.2 to 1
   Solution

   A is correct: with two independent pairs of characters, the four kinds appear in the proportions nine, three, three and one, the two middle classes being the new combinations. B is the ratio for a single character. C is the ratio of gametes, not of offspring. D corresponds to nothing in this cross.

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