Question

A triple heterozygote (AaBbCc) was mated to a triple recessive (aabbcc). The progeny were as follows:

ABC 4
aBC 335
aBc 48
ABc 127
abC 123
AbC 51
Abc 327
abc 5
The allele arrangement in the triple heterozygote must have been
a) A-B-C
b) A-c-B
c) a-B-C
d) a-c-b

Answer 1

The allele arrangement in the triple heterozygote is A-b-C based on the observed progeny phenotypes showing a high frequency of aBC and Abc, indicating the close linkage between B and C.

Step-by-step explanation:

The data provided suggests that the alleles for genes A, B, and C in the triple heterozygote are linked and show a significant excess of the parental phenotypes which are aBC and Abc. The least common phenotypes are ABC and ABC, which indicates that recombination between alleles is relatively rare in this specific case. Due to the large number of aBC and Abc offspring compared to the others, it is clear that the alleles B and C are very closely linked on the chromosome and do not assort independently.

The high frequency of aBC and Abc phenotypes signifies they are parental types, while the rare ABC and abc phenotypes point to recombinant types. Thus, in the triple heterozygote (AaBbCc), the alleles B and C must be on the same chromosome and closely linked to show such parental dominance in the offspring. The correct allele arrangement for the triple heterozygote is therefore A-b-C, which results in the observed high frequency of aBC and Abc offspring when crossed with a triple recessive phenotype (aabbcc).