The color of corn aleurone (kernel coat) is controlled by three genes: A, C and
ID: 96446 • Letter: T
Question
The color of corn aleurone (kernel coat) is controlled by three genes: A, C and R which are all needed for color. The gene encoding a dominant inhibitor of color, I is very closely linked to the C gene. Any one of the following genotypes results in colorless aleurone: I-, aa, cc, and rr. What is the expected colored: colorless ratio among F2 progeny from a cross of AAIICCRR to aaiiCCRR in the P generation? b. What proportion of the colorless F2 is expected to be homozygous for each of the 4 genes?
Explanation / Answer
In the present case one parent is having I and the other is having aa, so both will be colorless. Also, the F1 will have I, so again it will also be colorless.
Parents AAIICCRR (colorless) x aaiiCCRR (colorless)
F1 AaIiCCRR (colorless)
Gametes AICR,AiCR, aICR, aiCR
F2 Progeny
Gametes
AICR
AiCR
aICR
aiCR
AICR
AAIICCRR
Colorless
AAIiCCRR
Colorless
AaIICCRR
Colorless
AaIiCCRR
Colorless
AiCR
AAIiCCRR
Colorless
AAiiCCRR
Colored
AaIiCCRR
Colorless
AaiiCCRR
Colored
aICR
AaIICCRR
Colorless
AaIiCCRR
Colorless
aaIICCRR
Colorless
aaIiCCRR
Colorless
aiCR
AaIiCCRR
Colorless
AaiiCCRR
Colored
aaIiCCRR
Colorless
aaiiCCRR
Colorless
Out of the 13 possible colorless genotypes, 5 will be homozygous for I gene i.e. they will have II or ii. The genotypes are (AAIICCRR, AaIICCRR , AaIICCRR, aaIICCRR, aaiiCCRR). So, 5/13 colorless will be homozygous for gene I. Out of these 4/13 will be homozygous dominant (i.e. genotype II) and 1/13 will be homozygous recessive (i.e. genotype ii).
In case of the gene C and R, all the colorless genotypes will be homozygous for both the genes. In fact all will be dominant homozygous (CC and RR).
Also, the three genotypes out of the 13 colorless (AAIICCRR aaIICCRR, aaiiCCRR) will be homozygous for all the four genes.
Gametes
AICR
AiCR
aICR
aiCR
AICR
AAIICCRR
Colorless
AAIiCCRR
Colorless
AaIICCRR
Colorless
AaIiCCRR
Colorless
AiCR
AAIiCCRR
Colorless
AAiiCCRR
Colored
AaIiCCRR
Colorless
AaiiCCRR
Colored
aICR
AaIICCRR
Colorless
AaIiCCRR
Colorless
aaIICCRR
Colorless
aaIiCCRR
Colorless
aiCR
AaIiCCRR
Colorless
AaiiCCRR
Colored
aaIiCCRR
Colorless
aaiiCCRR
Colorless