Question

In Drosophila, Dichaete (D) is a mutation on chromosome III with a dominant effect on wing shape. It is lethal when homozygous. The genes ebony body (e) and pink eye (p) are recessive mutations on chromosome III. Flies from a Dichaete stock were crossed to homozygous ebony, pink flies, and the F₁ progeny, with a Dichaete phenotype, were backcrossed to the ebony, pink homozygotes. Using the results of this backcross shown in the table.
Table showing phenotypes and numbers of Drosophila offspring from a backcross involving Dichaete, ebony, and pink mutations.

Table showing phenotypes and numbers of Drosophila offspring from a backcross involving Dichaete, ebony, and pink mutations.

Diagram this cross, showing the genotypes of the parents and offspring of both crosses.

Accepted Answer

Step 1: Define the alleles and their dominance relationships. Dichaete (D) is a dominant mutation on chromosome III and lethal when homozygous (D/D lethal). ebony (e) and pink (p) are recessive mutations on the same chromosome. The wild-type alleles are d (for Dichaete), E (for ebony), and P (for pink). Step 2: Determine the genotypes of the parental flies in the initial cross. The Dichaete stock flies must be heterozygous for Dichaete (D/d) and carry wild-type alleles for ebony and pink (E/P), since ebony and pink mutations are recessive and not expressed in this stock. The ebony, pink flies are homozygous recessive for both ebony and pink (e/e, p/p) and wild-type for Dichaete (d/d). Step 3: Write the genotype of the F₁ progeny from the initial cross. Since D is dominant and lethal when homozygous, the F₁ flies with the Dichaete phenotype are heterozygous for Dichaete (D/d) and heterozygous for ebony and pink (E/e, P/p). Step 4: Diagram the backcross between the F₁ heterozygous flies (D/d, E/e, P/p) and the homozygous recessive ebony, pink flies (d/d, e/e, p/p). List all possible gametes from each parent considering the three loci and then combine them to predict offspring genotypes. Step 5: Use the phenotypic data from the backcross table to assign phenotypes to genotypes. For example, flies with Dichaete phenotype carry at least one D allele, ebony phenotype requires homozygous e/e, and pink phenotype requires homozygous p/p. This will help in confirming the parental genotypes and the arrangement of alleles on the chromosomes.

비슷한 문제에 대한 검증된 영상 답변:

주요 개념

Linkage and Recombination

Dominant and Recessive Mutations

Backcross and Genetic Cross Diagrams