Question

You are studying two traits in fruit flies:eye color where there are two colors, brown and redwing shape where there are straight and curled phenotypesYou mate two flies that are heterozygous for the genes that control both of these traits and get the following phenotypes in the following ratio:9 red and straight; 3 red and curled; 3 brown and straight; 1 brown and curledWhich alleles separated at which stages of meiosis?Select one:a. Red segregated from brown in meiosis II, and straight segregated from curled in meiosis II.b. Red segregated from brown in meiosis I, and straight segregated from curled in meiosis II.c. Red segregated from brown in meiosis II, and straight segregated from curled in meiosis I.d. Red segregated from straight in meiosis I, and brown segregated from curled in meiosis II.e. Red segregated from brown in meiosis I, and straight segregated from curled in meiosis I.

Answer 1

Answer:

e. Red segregated from brown in meiosis I, and straight segregated from curled in meiosis I.

Explanation:

A cross between two flies heterozygous for both genes produced an offspring with the phenotypic ratio of 9:3:3:1. This ratio is expected according to Mendel's law of independent assortment, which states that alleles of the same gene assort independently during gamete formation.

Before meiosis starts in flies, a single diploid cell duplicates its DNA, so each chromosome has 2 sister chromatids that contain the same information.

• During meiosis I, the homologous chromosomes separate into two daughter cells. The chromosome number is reduced by half, but each chromosome has two sister chromatids.
• During meiosis II, the sister chromatids separate and each daughter cell from meiosis I divides into two new daughter cells (to get the total of 4 haploid cells).

In a heterozygous fly, each homologous chromosome contains a different allele, and the sister chromatids are copies that carry the same allele. For that reason, both traits were segregated during meiosis I.