Assume that investigators crossed a strain of flies carrying the dominant eye mu
ID: 57658 • Letter: A
Question
Assume that investigators crossed a strain of flies carrying the dominant eye mutation Lobe on the second chromosome to a strain homozygous for the second chromosome mutations smooth abdomen and straw body. The F1 Lobe females were then backcrossed to homozygous smooth abdomen, straw body males and the following phenotypes were observed: (Note- be careful what you label as a double cross-over). smooth abdomen, straw body 820 Lobe 780 smooth abdomen, Lobe 42 straw body 58 smooth abdomen 148 Lobe, straw body 152
a) Give the gene sequence and map units between these three loci.
b) What is the coefficient of coincidence?
c) What is the interference?
Explanation / Answer
l = lobe; a = smooth abdomen; s = straw body
The genotypes of F2 generation are as follows:
l + + = 780
+ a s = 820
l a + = 42
+ + s = 58
+ a + = 148
l + s = 152
Now here two genotypes are not mentioned, which are-
l a s = 0
+ + + = 0
Part a-
By looking at the frequencies, we can see that [l a + = 42 and + + s = 58] are double crossovers. The maximum ones [780 and 820] are parental genotypes. By comparing them we can find that the order of genes is-
lobe---------smooth abdomen--------straw body
Distance between a and s = 148+152+42+58/ 2000 = 20 cM
Distance between l and s = 0 + 0 + 42+58/2000 = 5 cM.