Question

The genotype of the heterozygous parent in the previous question was AB/ab. Were these genes in cis (coupled) or trans (repulsion)?

1) Cis (coupled)
2) Trans (repulsion)
3) Cannot be determined from the data

Answer 1

The genotype 'AB/ab' indicates the genes are in trans (repulsion) configuration. This is because the dominant and recessive alleles are found on different chromosomes, which can result in nonparental genotype combinations after recombination.

Step-by-step explanation:

The genotype 'AB/ab' indicates the genes are in trans (repulsion) configuration because dominant and recessive alleles are on opposite chromosomes.

In a heterozygous individual who inherited dominant maternal alleles (AB) and recessive paternal alleles (ab) for two genes on the same chromosome, if the alleles are in cis configuration (also called coupled), both dominant or both recessive alleles would be on the same chromosome. However, with a trans configuration (also called repulsion), each chromosome carries one dominant and one recessive allele.

Therefore, when discussing this heterozygous individual, the occurrence of the nonparental genotypes (Ab and aB) suggests that recombination can occur during meiosis even when genes are linked. However, as the parental genotypes (AB and ab) appear more frequently, it indicates that linkage between the genes is strong, yet not absolute. This results in a high proportion of parental type offspring compared to the recombinant types in the progeny of such crosses.