In zebrafish, three genes have been mapped on the third chromosome, in the order
ID: 81562 • Letter: I
Question
In zebrafish, three genes have been mapped on the third chromosome, in the order
fiz---6 m.u.---myob-------14 m.u.-------sufi
The wild-type allele of each gene is dominant.
A strain that is
fiz myob sufi / + + +
is testcrossed, and there are 1000 offspring fish.
a. How many wild-type offspring would you expect to see in these 1000 offspring?
b. How many fiz + + offspring would you expect to see in these 1000 offspring?
c. How many + + sufi offspring would you expect to see in these 1000 offspring?
d. How many + myob + offspring would you expect to see in these 1000 offspring?
Explanation / Answer
Answer:
a). 808.36
b). 25.8
c). 65.8
d). 4.2
Explanation:
Distance between the genes = Recombinaiton frequency
Double cross over frequency = 6% * 14% = 84% = 0.84
Out of 1000 = 0.84 * 1000 = 8.4
Double cross over progeny = fiz---+ ---sufi (0.42) & +----myob---+ (0.42)
While calculating individual single cross over progeny, we must substract the double cross overs from each single cross over progeny, then we will get actual single cross over progeny.
The recombinant progeny, if single cross over occurs between fiz and myob = 6% out of 1000 = 60
The progeny = 60-8.4 = 51.6
Fiz-----myob ----sufi / + ---+-----+
After single cross over occurs between fiz and myob, the progeny are Fiz----+----+ (25.8) & +---myob---sufi (25.8).
The recombinant progeny, if single cross over occurs between myob and sufi = 14% out of 1000 = 140
The progeny = 140-0.84 = 131.6
Fiz-----myob ----sufi / + ---+-----+
After single cross over occurs between myob and sufi, the progeny are Fiz----myob----+ (65.8) & +---+---sufi (65.8).