1) In silkmoths, Bombyx mori , red eyes ( re ), white-banded wings ( wb ), and h
ID: 35728 • Letter: 1
Question
1) In silkmoths, Bombyx mori, red eyes (re), white-banded wings (wb), and hirsute trunk (ht) are encoded by mutant alleles that are recessive to those produced by the wild-type (re+, ht+, and wb+, respectively). A testcross was made between an individual whose genotype was re+re wb+wb ht+ht and a complete wild type. The following offspring were found (n.b. I omitted the re wb ht alleles from the homozygous recessive parent in the offspring for brevity);
re wb+ ht+ 580
re wb+ ht 3
re wb ht+ 45
re+ wb ht 592
re wb ht 89
re+ wb+ ht 40
re+ wb+ ht+ 94
re+ wb ht+ 5
A) Were pairs of loci in the heterozygote individual in the testcross in coupling or repulsion for this experiment?
B) Test the hypothesis: HO: Loci for red eyes and white banded wings are independent.
C) What is the gene order of these loci and how far apart are they?
D) Is there evidence of interference?
Explanation / Answer
A)pairs of loci are in coupling
b) since the map distance between red eyes and white banded wings is 13.1% (map.units) they are independently assorted.
c) order of genes
Minimum number of progeny is the one which have double crossovers (DCOs)
On analyzing the number of progeny obtained we can, thus, identify them as follows:
re+ wb ht+ 5
re wb+ ht 3 DCOs
by looking at the above two we can identify the order of genes.
"re wb ht"
The distance between the genes is wb& ht= single crossovers(SCOs) + DCOs/total (1448) X 100= 45+40+3+5/1448 X 100=0.0642/100 =6.42 m.u
similarly, re & wb =0.1319/100 =13.19 mu
d) interference can be calculated as follows:
first, calculate coefficient of coincidence= no. of observed DCOs/ no. of expected DCOs
=8/ 0.06X0.131X1448
=8/12.14
coefficient of coincidence =0.65
thus, interference= 1- coefficient of coincidence
=1-0.65
=0.34 i.e 34% of the expected DCOs are not seen in the progeny population.
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