In a plant, the colour of grains is controlled by 3 genes located on separate chromosomes. Gene 'C' and 'R' independently do not form any colour, but when together, they impart greenish-brown colour to the stem, while the grains remain colourless. In presence of an additional allele 'A', the stem as well as grains become violet. In a trihybrid cross, what phenotypic ratio is expected in grains?

Question

In a plant, the colour of grains is controlled by 3 genes located on separate chromosomes. Gene 'C' and 'R' independently do not form any colour, but when together, they impart greenish-brown colour to the stem, while the grains remain colourless. In presence of an additional allele 'A', the stem as well as grains become violet. In a trihybrid cross, what phenotypic ratio is expected in grains?, 48 coloured : 16 colourless, 36 coloured : 28 colourless, 27 coloured : 37 colourless, 40 coloured : 24 colourless

MARKS App · Accepted Answer

According to the data given, coloured seed can be produced in the plant only when the genotype has at least one dominant C gene and one dominant R gene and one dominant A gene, that is C _ R _ A _ A trihybrid cross is C c R r A a x C c R r A a . The three genes are on separate chromosomes. Thus, they are independently assorted. If we consider the three genes separately: C c x C c will produce 1 CC, 2 Cc and 1 cc. Thus, the proportion of individuals having CC or Cc is 3 4 . Similarly, R r x R r will produce 1 RR, 2 Rr and 1 rr. Thus, the proportion of individuals having RR or Rr is 3 4 . Similarly, A a x A a will produce 1 AA, 2 Aa and 1 aa. Thus, the proportion of individuals having AA or Aa is 3 4 . Thus, the proportion of plants with genotype C _ R _ A _ in trihybrid cross will be 3 4 × 3 4 × 3 4 = 27 64 . Thus, 27 out of 64 progenies will have coloured grains. The remaining 37 out of 64 will have colourless grains.

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