Genetics question?

Question

In Drosophila, Dichaete (D) is a chromosome 3 mutation with a dominant effect on wing shape. It is lethal when homozygous. The genes ebony (e) and pink (p) are chromosome 3 recessive mutations affecting body and eye color, respectively. 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. The results of this back cross were

Phenotype
Number

Dichaete
401

ebony, pink
389

Dichaete, ebony
84

pink
96

Dichaete, pink
2

ebony
3

Dichaete, ebony, pink
12

wild type
13


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

(b) What is the sequence of and interlocus distance between these three genes?

Answer 1

P1 DdEEPP x ddeepp yields ddEePp and DdEePp

F1 cross only DdEePp x DdEePp
Note: these are actually all:
DEP
===
dep

F2 every possible combination will occur, but DDs will die. The rate of crossing over depends on the distance between the genes.