A strain of flies carrying the dominant eye mutation Lobe on the second chromoso
ID: 47472 • Letter: A
Question
A strain of flies carrying the dominant eye mutation Lobe on the second chromosome was crossed 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
What are the gene order and map units for the three loci?
Explanation / Answer
The order of genes is straw body, smooth abdomen, and lobe.
Total number of offspring
= 820+42+148+780+152+58
= 2000
Frequency of smooth abdomen, straw body
= 820/2000
= 0.41
Frequency of smooth abdomen, Lobe
= 42/2000
= 0.021
Frequency of smooth abdomen
= 148/2000
= 0.074
Frequency of Lobe
= 780/2000
= 0.39
Frequency of Lobe, straw body
= 152/2000
= 0.076
Frequency of straw body
= 58/200
= 0.029
Basing on the frequencies the order of genes is straw body, smooth abdomen, and lobe.
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