Question

which of the follow indicates the mean number per cross of f₂ plants producing medium - red grain and correctly explains the distribution of the phenotypes? a the mean number of medium - red phenotypes per cross is 20.8. the distribution of phenotypes suggests that grain color is under environmental control. b the mean number of medium - red phenotypes per cross is 20.8. the distribution of phenotypes suggests that multiple genes are involved in grain color determination. c the mean number of medium - red phenotypes per cross is 104. the distribution of phenotypes suggests that grain color is under environmental control. d the mean number of medium - red phenotypes per cross is 104. the distribution of phenotypes suggests that multiple genes are involved in grain color

Explanation:

To determine the correct option, we analyze the mean calculation and the phenotypic distribution. First, for the mean number of medium - red phenotypes per cross, if we assume the total number of plants in the cross (sum of all phenotypes) and the proportion of medium - red, the mean of 20.8 (calculated as, for example, if the total number of plants across crosses is such that when divided by the number of crosses, gives 20.8) is more reasonable than 104. Then, regarding the distribution of phenotypes: a distribution that shows a range of phenotypes (like different shades of red including medium - red) for a trait like grain color is characteristic of polygenic inheritance (multiple genes involved). Environmental control would imply that the phenotype is more influenced by the environment, but the distribution here is more consistent with multiple genes (polygenic) affecting the trait. Option A is wrong because grain color being under environmental control is not supported by the phenotypic distribution pattern. Option C has an incorrect mean (104 is too high) and the environmental control explanation is wrong. Option D has an incorrect mean. So option B is correct as it has the correct mean (20.8) and the correct explanation about multiple genes being involved.

Answer:

B. The mean number of medium - red phenotypes per cross is 20.8. The distribution of phenotypes suggests that multiple genes are involved in grain color determination.