Question

In Drosophila, the genes j and r are linked. Parental flies of genotype j+ r+/ j+ r+ and j r/ j r are crossed. What allele arrangement would the F1 flies contain?

a) j+ r/ j r
b) j+ r+/ j r
c) j+ r+/ j+ r
d) j r/ j r+

Answer 1

The F1 flies resulting from the cross of parental flies with genotypes j+ r+/ j+ r+ and j r/ j r in Drosophila, where genes j and r are linked, would most likely have the allelic arrangement j+ r/ j r. Option a is the correct answer.

Step-by-step explanation:

In a Drosophila genetics problem involving linked genes, parental flies with genotypes j+ r+/ j+ r+ and j r/ j r are crossed to determine the allele arrangement of the F1 offspring. Linked genes, such as j and r in this scenario, do not assort independently and are transmitted together during gamete formation unless crossing over occurs during meiosis.

Therefore, the expected genotypic combination in the F1 generation would predominantly be the parental types, assuming no or very low recombination between the linked genes.

Given that the parents are homozygous for either the dominant or recessive alleles and there are no new allele combinations introduced by crossing over, F1 progeny would mainly represent the parental genotype combinations.

Therefore, the F1 flies would contain a genotype of j+ r/ j r, which is option (a). The F1 generation would exhibit the dominant phenotypes due to the presence of dominant j+ and r+ alleles.