Question

Two different genes, located on two different chromosomes, are responsible for color production in the aleurone layer of com kernels. For color production (either purple or red), the dominant alleles of these two genes \((C \text { and } R\) ) must come together. Furthermore, a third gene, located on a third chromosome, interacts with the \(C\) and \(R\) alleles to determine whether the aleurone will be red or purple. While the dominant allele ( \(P\) ) ensures purple color, the homozygous recessive condition (pp) makes the aleurone red. Determine the \(\mathrm{P}_{1}\) phenotypic ratio of the following crosses: (a) \(C C r r P P \times \operatorname{ccRRp} p\) (b) \(C c R R p p \times C C R r p p\) (c) \(\operatorname{CcRrPp} \times\) CcRrpp.

Short answer

Answer: The phenotypic ratios of the offspring for each cross are as follows: (a) 100% Purple, (b) 100% Purple, and (c) 2:1 Purple:Red.

Step-by-step solution

Cross (a): CCrrPP x ccRRpp

In this cross, we will first determine the gametes produced by each parent and then find the possible genotypic combinations for the offspring. Since C and R are dominant and required for color production, we will need the presence of at least one C and R allele for the color to be expressed: Parent 1: CCrrPP - gametes: CRP and CRp Parent 2: ccRRpp - gametes: cRp Offspring genotypes: CcRRPp Since the offspring has at least one C and R allele, color will be produced. The presence of the dominant P allele ensures a purple color. Therefore, the P1 phenotypic ratio for this cross is: 100% Purple

Cross (b): CcRRpp x CCRRpp

In this cross, we will follow the same procedure as before to determine the possible genotypic combinations: Parent 1: CcRRpp - gametes: CRp and cRp Parent 2: CCRRpp - gametes: CRp Offspring genotypes: CCRRpPp and CcRRPp Both genotypes have at least one C and one R allele, so color will be produced. However, both genotypes are heterozygous for the P gene (Pp), which results in a purple color. The P1 phenotypic ratio for this cross is: 100% Purple

Cross (c): CcRrPp x CcRrpp

This cross involves all heterozygous parents with respect to the three genes. To find the gametes produced by each parent, we need to consider the possible allele combinations for each gene. Parent 1: CcRrPp - gametes: CRP, CRp, cRP, cRp Parent 2: CcRrpp - gametes: CRp, cRp Now, let's find the possible genotypic combinations for the offspring and the corresponding phenotypes by considering the presence of the required alleles: Offspring genotypes and phenotypes: 1. CCRrPp (Purple) 2. CcRRPp (Purple) 3. CCRrpP (Purple) 4. CcRrpP (Purple) 5. CcRRpp (Red) 6. CcRrpp (Red) The P1 phenotypic ratio for this cross is: 4:2 or 2:1 Purple:Red