DESIGNING AN EXPERIMENT TO TEST INDEPENDENT ASSORTMENT Imagine that you are work
ID: 34331 • Letter: D
Question
DESIGNING AN EXPERIMENT TO TEST INDEPENDENT ASSORTMENT
Imagine that you are working in a fruitfly (Drosophila) genetics laboratory. Two new mutations have been recently discovered. Warty eyes (w) is recessive to normal eyes (W) at the warty locus. Hairy (h), the presence of extra sensory bristles, is recessive to normal (H). Assume that you have a pure breeding strain of each recessive phenotype (wwHH and WWhh) and a third strain that is pure breeding for both mutants (wwhh). Diagram the experimental design of crosses that you would use to test the null hypothesis that these two loci segregate independently; the alternative hypothesis is that they are linked. Design your crosses using the three strains described above. Make sure that you show exactly what experimental results you would use to test the null hypothesis of independent assortment. Please note: there is no recombination between loci on the same chromosome in male Drosophila because there are no crossovers (chiasmata) during meiosis in male Drosophila.
Explanation / Answer
Null Hypothesis - two loci segregate independently
Alternative hypothesis - two loci are linked
In order to test our null hypothesis, let us cross the parents with each recessive phenotype (wwHH and WWhh)
Parents - wwHH x WWhh
F1 progeny - WwHh (100%) (Ratio - )
Self fertilization of F1 progeny will result in -
Parents - WwHh x WwHh
WH
Wh
wH
wh
WH
WWHH
WWHh
WwHH
WwHh
Wh
WWHh
WWhh
WwHh
Wwhh
wH
WwHH
WwHh
wwHH
wwHh
wh
WwHh
Wwhh
wwHh
wwhh
F2 Progeny - WWHH: 56.3 %
WWhh: 18.8 %
wwHH: 18.8 %
wwhh: 6.3 %
F2 progeny showed to be in the ratio 9:3:3:1 which is typical of dihybrid cross, any deviation from this ratio would indicate gene linkage.
Since the ratio observed was that of a typical dihybrid cross, we can acccept the null hypothesis.
WH
Wh
wH
wh
WH
WWHH
WWHh
WwHH
WwHh
Wh
WWHh
WWhh
WwHh
Wwhh
wH
WwHH
WwHh
wwHH
wwHh
wh
WwHh
Wwhh
wwHh
wwhh
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