n corn, three gene loci control color of the aleurone layer of the kernel (which
ID: 55164 • Letter: N
Question
n corn, three gene loci control color of the aleurone layer of the kernel (which gives the kernel its color). Each locus has two alleles; C is dominant to c, R is dominant to r, and P is dominant to p. The presence of at least one dominant allele at each of the three loci produces a purple aleurone. If the kernel is homozygous recessive at the “P” locus, but each of “C” and “R” possess one dominant allele, the aleurone is red. If either the “C” locus or “R” locus is homozygous recessive, the aleurone is white, regardless of the state of the “P” locus.
a. What sort of genetic phenomenon does this relationship demonstrate?
b. Briefly explain what it is about this situation that demonstrates the phenomenon (relationship) you named in the blank above.
c. What color aleurone do you expect in kernels of the following genotypes? CC rr PP ______________________.
CC Rr Pp ______________________.
CC rr Pp ______________________.
CC Rr Pp ______________________.
Cc RR pp ______________________.
cc Rr Pp ______________________.
d. Describe (or diagram) a simple, but sufficient, biochemical pathway model that would explain this relationship. (The model may be hypothetical)
Explanation / Answer
a) Recessive epistasis. Recessive alleles at one locus mask the phenotypic expression of other gene locus such epistasis is called recessive epistasis.
b) Complete dominance at both gene pairs (C, R), but either recessive homozygote is epistatic to the effect of the other gene. To be more precise, the above phenomenon is an example of Duplicate recessive gene epistasis (9:7)
c) CCrrPP : white
CCRrPp : Purple
CCrrPp : white
CCRrPp : purple
CcRRpp : red
ccRrPp : white
d) For the aleurone to be red colored, alleles C and R must be present. The homozygous recessive of either allele (c/c or r/r) disrupts anthocyanin production and results in a colorless aleurone. Genes C and R are located on separate chromosomes and segregate independently. The allele P interacts with alleles C and R to produce a purple aleurone. The homozygous recessive condition (pr/pr) interacts with C and R to produce a red aleurone.
Cc Rr Pp purple aleurone
Cc Rr pp red aleurone
cc Rr Pp white aleurone
Cc rr Pp white aleurone
C + R ---------- red
C + R + P --------- purple
Related Questions
Navigate
Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.