The table shows offspring from a fish farm breeding experiment. A female guppy with a black tail was crossed with a male guppy with a white tail. In this sp...
Question 1 Report
The table shows offspring from a fish farm breeding experiment. A female guppy with a black tail was crossed with a male guppy with a white tail. In this species, the allele B for black tail is dominant to b for white tail. The fish farmer kept the offspring in identical tanks with the same food, water temperature and oxygen level. This reduced environmental differences when the tail colour of young fish was recorded.
| Tail colour of offspring | Number of male fish | Number of female fish |
|---|---|---|
| Black | 39 | 42 |
| White | 41 | 38 |
(a) Calculate the total number of offspring fish with black tails. [1]
(b) Use Table 1 to state the approximate ratio of black-tailed offspring to white-tailed offspring. [1]
(c) Complete the likely genotypes of the parents in the cross, using B and b. [2]
(d) Explain why male and female offspring have similar numbers of each tail colour in Table 1. [2]
Answer Details
(a)
\[39+42=81\]
There are 81 black-tailed offspring. [1 mark]
(b) Black-tailed offspring total \(81\); white-tailed offspring total \(41+38=79\). This is approximately 1:1. [1 mark]
(c) The white-tailed male must be \(bb\), because white is recessive. [1 mark] A \(1:1\) black:white offspring ratio from a black parent and a \(bb\) parent indicates that the black-tailed female is \(Bb\). [1 mark]
(d) Tail colour is inherited independently of sex, so the allele is not sex-linked. [1 mark] Both male and female offspring can receive \(B\) or \(b\) from their parents, giving similar numbers of each colour in a sufficiently large group. [1 mark]
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