Figure 13.11

-The F2 phenotypic ratio of 9:3:4,as shown above,is a result of a cross involving
A) two genes expressing complete dominance.
B) a gene expressing dominance and another gene expressing codominance.
C) two genes expressing codominance.
D) epistasis, in which one gene modifies the expression of the other gene.
E) multiple alleles.

Question

Figure 13.11
 
-The F2 phenotypic ratio of 9:3:4,as shown above,is a result of a cross involving  
A) two genes expressing complete dominance. 
B) a gene expressing dominance and another gene expressing codominance. 
C) two genes expressing codominance. 
D) epistasis, in which one gene modifies the expression of the other gene. 
E) multiple alleles.

Quizplus · Accepted Answer

The 9:3:4 phenotypic ratio is indicative of epistasis, in which one gene modifies the expression of the other gene. This ratio can be seen in a cross between individuals that are heterozygous for two genes, where one gene masks the expression of the other gene. For example, if gene A is required for pigment production and gene B determines the type of pigment produced, a dominant allele of gene A would mask the expression of gene B, resulting in a 9:3:4 phenotypic ratio.

Figure 13.11 -The F2 Phenotypic Ratio of 9:3:4,as Shown Above,is a Result