Question

you perform a three point cross using genes x, y, and z, which are located in that order (xyz) on the chromosome. following convention, upper-case alleles are dominant and lower-case alleles recessive. in the f0 generation you use one x y z individual from a true-breeding population, and one x y z individual from another true-breeding population. which f2 genotype requires a double crossover event?

Answer 1

The F2 genotype requiring a double crossover event in a three-point cross would involve an individual with one allele from each true-breeding parent for the middle gene and the other alleles from the other parent. This happens due to two crossovers during meiosis, which exchange the middle gene while keeping the outer genes aligned with their original parent.

Step-by-step explanation:

The F2 genotype that requires a double crossover event in a three-point cross of genes X, Y, and Z from true-breeding parents X Y Z and x y z would be one in which the middle gene's allele is from one parent and the flanking genes' alleles are from the other parent (e.g., X y Z or x Y z). This outcome is due to the recombination of the alleles during gamete formation, where two crossover events are necessary to exchange the middle allele while keeping the original order of the flanking alleles intact.

In genetics, a three-point cross is used to determine the order of genes on a chromosome and the distances between them. True-breeding (homozygous) individuals produce offspring that carry the same genotype and, hence, the same phenotype for a given trait. However, when they are crossed with other true-breeding individuals that have different alleles for those genes, the resulting F1 generation consists of heterozygotes displaying the dominant phenotype. Upon further crossing to produce an F2 generation, the assortment of alleles leads to various combinations due to genetic recombination during meiosis.