3. A line of Drosophila melanogaster with ebony body and sepia eyes (line A) is

Question

3. A line of Drosophila melanogaster with ebony body and sepia eyes (line A) is
crossed to a line with tan body and red eyes (line B). The F1 are all tan-bodied, redeyed.
a) (one point) What proportion of gametes produced by the F1 have the dominant
allele for both loci? What proportion of the gametes produced by line B have the
dominant allele for both loci?
Next, imagine that An F1 female is crossed to a male from line A.
If 1000 offspring were scored for both characters, what number of offspring would
be expected to have each of the four phenotypes (assuming no linkage)? List them
below.
Now imagine that the following data were actually collected from the cross above:
Body Eyes
Tan normal 491
Tan sepia 9
Ebony normal 8
Ebony sepia 492
b) (one point) Are the loci linked? If so, how many map units are they apart ? Do a
?2 test and show your work below. Diagram this cross.

Explanation / Answer

e: ebony; E: tan body s: sepia: S: red eyes P: eess x EESS F1: EeSs (tan-red) What proportion of gametes produced by line A have the dominant allele for both loci? => 0 (line A has genotype eess) What proportion of the gametes produced by the F1 have the dominant allele for both loci? => 1/2 (for linked) => 1/4 (for unlinked) An F1 female is crossed to a male from line A. If the two genes are unlinked: 250 tan-red 250 tan-sepia 250 ebony-red 250 ebony-sepia Now imagine that the following data were actually collected from the cross above: Body Eyes Tan normal 411 Tan sepia 89 Ebony normal 87 Ebony sepia 413 Are the loci linked? => Yes For the linked genes, the proportion of the gametes would be m : n : n : m ; where 'm' is parental types and 'n' is recombinant types, and m > n. If so, how many map units are they apart ? (89+87)/(411+89+87+413) x 100 = 17.6 mu ~~> 18 mu Do a x^2 test and show your work below: obs: observed exp: expected d = obs - exp --Phenotype--| obs |. exp | d | d^2 | d^2/e | Tan normal -- | 411 | 410 | 1 |..1....| 0.002 Tan sepia ---- |. 89 |... 90 | -1 |.1....| 0.011

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