Question

Grain colour in wheat is determined by three pairs of polygenes. Following cross AABBCC (dark color) \[\times \] aabbcc (light color), in \[{{F}_{2}}\] generation what proportion of the progeny is likely to resemble either parent?
A. Half
B. Less than 5 per cent
C. One third
D. None of the above

Answer 1

Hint: Polygenic inheritance refers to inheritance in which a train is governed by more than one gene. The dominant allele of each gene is able to express only a part of the trait. The full trait is only expressed in presence of dominant alleles of all multiple genes. The total progeny produced in \[{{F}_{2}}\] generation of the given cross is 64 and only 2 resembles either parent.

Complete answer: Wheat shows polygenic inheritance and this means that a single trait is determined by more than one gene. This is also evident in skin colour inheritance in humans.

Now, polygenes in wheat for colour determination are A, B, and C (dominant alleles for dark colour) and a, b, and c (recessive alleles for light colour). The parents in the given statement are having pure dark colour character and pure light colour character. The cross between them will produce \[{{F}_{1}}\] generation all having genotype AaBbCc. These are called hybrids and show 8 gamete types that can form a total of 64 genotypes. On self-crossing the two hybrids we will get \[{{F}_{2}}\] generation with 64 distinct genotypes. The \[{{F}_{2}}\] generation will show only two with resembling characters to either parent. One will show AABBCC and the other will show aabbcc. Thus, 2 from 64 shows a resemblance to either parent. We can divide them and then multiply with 100 to know the percentage of individuals resembling either parent. So, $\frac{2}{64}\times 100=3.12%$ which is less than $5%$.
Therefore, option B is the correct answer.

Note: Wheat is a major source of carbohydrates and vegetable proteins. It is one of the world’s most grown crops. It forms the major portion of the staple diet in the world. The most common species of wheat is T. aestevium. Different genotypes are responsible for different traits seen in diverse wheat species.