Two genes interact to produce various phenotypic ratios among F2 progeny of a di
ID: 51741 • Letter: T
Question
Two genes interact to produce various phenotypic ratios among F2 progeny of a dihybrid cross. Design a different pathway explaining each of the F2 ratios below, using hypothetical genes R and T and assuming that the dominant allele at each locus catalyzes a different reaction or performs an action leading to pigment production. The recessive allele at each locus is null (loss-of-function). Begin each pathway with a colorless precursor that produces a white or albino phenotype if it is unmodified. The ratios are for F2 progeny produced by crossing wild-type F1 organisms with the genotype RrTt.
12/ 16 white: 3/16 green: 1/16 yellow
C)At least one copy of each dominant allele results in white, at least one copy of either dominant allele produces green, and the absence of either dominant allele produces yellow.
WHICH STATEMENT IS CORRECT. PLEASE HELP EXPLAIN STEP BY STEP SO I CAN DO THE REST!
A) At least one copy of both dominant alleles results in white; at least one copy of one of the dominant alleles also results in white, but at least one copy of the other dominant allele produces green; and the absence of either dominant allele produces yellow. B) If both dominant alleles are present, the result is green. At least one copy of one specific dominant allele is required for yellow. If that dominant allele is not present, the result is white, regardless of whether the other dominant allele is present.C)At least one copy of each dominant allele results in white, at least one copy of either dominant allele produces green, and the absence of either dominant allele produces yellow.
WHICH STATEMENT IS CORRECT. PLEASE HELP EXPLAIN STEP BY STEP SO I CAN DO THE REST!
Explanation / Answer
ANSWER
The statement A is correct
At least one copy of both dominant alleles results in white; at least one copy of one of the dominant alleles also results in white, but at least one copy of the other dominant allele produces green; and the absence of either dominant allele produces yellow.
Explanation:
The present cross is a type of epistasis namely Dominant epistasis
Dominant epistasis caused by the dominant allele of one gene, masking the action of either allele of other gene. The ratio obtained F2 progeny is 12:3:1.
When dominant allele ‘A’ masks the expression of ‘B’, ‘A’ is epistatic gene of ‘B’. ‘A’ can express itself only in the presence of ‘B’ or b allele. Therefore it is called dominant epistasis. Complete dominance at both gene pairs, but one gene, when dominant, epistatic to the other.
From the data given
Alleles R and r are for colour expression
R denotes white coloured (weak coloration) and r is a recessive denotes for yellow colored
At another locus T for Green color , T is dominant to t= Green colour, t is recessive gives yellow colour.
Both r and t when present in recessive conditions both gives yellow fruit colour.
RRrr X TTtt
Gametes produced are Rr and Tt
The progeny produced in F1 generation are RrTt – All are white
If we crossed F1 progeny with RrTt then as follows
RrTt X RrTt
Then F2 progeny as follows
Gamates
RT
Rt
rT
rt
RT
RRTT, White
RRTt, White
RrTT, White
RrTt, White
Rt
RRTt, White
RRtt, White
RrTt, White
Rrtt, White
rT
RrTT, White
RrTt, White
rrTT Green
rrTt, Green
rt
RrTt, White
Rrtt, White
rrTt , Green
rrtt, Yellow
The F2 progeny phenotypic ratio is 12 white : 3 green : 1 yellow.
Gamates
RT
Rt
rT
rt
RT
RRTT, White
RRTt, White
RrTT, White
RrTt, White
Rt
RRTt, White
RRtt, White
RrTt, White
Rrtt, White
rT
RrTT, White
RrTt, White
rrTT Green
rrTt, Green
rt
RrTt, White
Rrtt, White
rrTt , Green
rrtt, Yellow
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