WRITE A QUESTION AND ANSWER Ask a question that asks one to

WRITE A QUESTION AND ANSWER: Ask a question that asks one to identify a. Either one of the phenotypes in a 9:3:3:1 distribution or frequency of one of the phenotypes. It cannot ask for the whole distribution but only part of it. b. Asks to identify the different genotypes within a phenotypic class. You have to find a way to elicit this answer without describing the genotype (“heterozygous at one locus”) but by characteristic.

Solution

a)

How to classify the different phenotypes present in the F2 progeny?

If the phenotypic ratio is 9:3:3:1, it means that four different types of appearances are present in the progeny. For example, round wrinkled and green yellow dihybrid seeds. Irrespective of which allele or gene is dominant or which gene is recessive, ultimately the final appearance of the individual seed indicates the phenotypic ratio. The ratio of the numbers of four different phenotypes round yellow, round green, wrinkled yellow and wrinkled green is written as phenotypic ratio.

b)

How to classify the various genotypes in a phenotypic class?

In the phenotypic ratio 9:3:3:1, the phenotypic class 9 has a set of genotypes. Suppose, the phenotypic class represents round yellow phenotype, as round is dominant over wrinkled, two alleles of round (one genotype) or one allele of round along with one allele of wrinkled (another genotype), both will give rise to round phenotype. But, there are two genotypes in this case. Simultaneously, two alleles of yellow (one genotype) or one allele of yellow and one allele of green (another genotype), both will give rise to yellow phenotype as yellow is dominant over green. But, there are two genotypes existing here.

So, there might be various classes of genotypes in one phenotypic class of 9 (round yellow). Same is the case with 3 and 1 phenotypic classes.