Question

Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second

chromosome with a strain homozygous for the second chromosome recessive mutations smooth abdomen and
straw body. The F1 Lobe females were then backcrossed with homozygous smooth abdomen, straw body males, and
the following phenotypes were observed:
smooth abdomen, straw body 820
Lobe 780
smooth abdomen, Lobe 42
straw body 58
smooth abdomen 148
Lobe, straw body 152
Give the gene order of these three loci.
A) smooth, Lobe, straw
B) it is impossible to tell
C) Lobe, smooth, straw
D) smooth, straw, Lobe
E) Lobe, straw, smooth

Answer 1

The gene order of the three loci in the cross between the strains of flies is smooth, Lobe, straw.

Step-by-step explanation:

In this question, we are given the phenotypes observed from a cross between a strain of flies carrying the dominant eye mutation Lobe and a strain homozygous for the recessive mutations smooth abdomen and straw body. From the observed phenotypes, we can determine the gene order of these three loci.

The phenotypes observed are as follows:

• smooth abdomen, straw body: 820
• Lobe: 780
• smooth abdomen, Lobe: 42
• straw body: 58

Based on these observations, we can conclude that the gene order of these three loci is smooth, Lobe, straw. Therefore, the correct answer is A) smooth, Lobe, straw.