Agapanthus is a dominant, homozygous lethal trait among Telorites from the plane
ID: 132003 • Letter: A
Question
Agapanthus is a dominant, homozygous lethal trait among Telorites from the planet Teleflora. Subjects with this condition love to send flowers. From a group of Telorites heterozygous at the Agapanthus locus (with two alleles: A = dominant (trait) allele, a = recessive (wild-type) allele), 88% of the Telorites have the Agapanthus phenotype, and 12% look wild-type.
Also, true-breeding wild-type Telorites (aa genotype) have 0% penetrance.
A Telorite with the Agapanthus phenotype mates with a true-breeding Telorite with the wild-type phenotype. One of the F1 children is randomly selected and is mated back to the true-breeding wild-type parent. Out of three F2 individuals, we only observe the wild-type phenotype.
The genotype of the randomly-selected F1 subject must be:
A. AA.
B. We cannot say with certainty.
C. Aa.
D. aa.
E. Aa and aa.
Explanation / Answer
Option D. aa
Heterozygous Agapanthus - Aa
True-breeding Telorites wild type- aa
crossing Agapanthus and true breeding wild type - Aa X aa
F1 generation- Aa Aa aa aa
As per question; one random F1 child is mated with wild type:
Therefore; if we take 'Aa' and mate with wild type: Aa X aa
F2 generation- Aa Aa aa aa (2 wild-type and 2 Agapanthus)
if we take 'aa' and mate with wild type: aa X aa
F2 generation- aa aa aa aa (all wild type)
As per given condition, 3 F2 individuals have wild type phenotype. This is possible only if the randomly selected F1 subject is aa.