Assume that investigators crossed a strain of flies carrying the dominant eye mu
ID: 33980 • Letter: A
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. What is the order of the genes?
smooth abdomen, straw body 820
smooth abdomen, Lobe 42
smooth abdomen 148
Lobe 780
Lobe, straw body 152
straw body 58
a. smooth abdomen, straw body, lobe
b. straw body, smooth abdomen, lobe
c. straw body, lobe, smooth abdomen
Explanation / Answer
The order of genes is straw body, smooth abdomen, lobe. Option b is correct.
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 = 58/2000 = 0.029
Basing on the frequencies the order of genes is straw body, smooth abdomen, lobe.