3. In Drosophila, the genes sr (stripe thorax) and e (ebony body) are 8 m.u. apa
ID: 200368 • Letter: 3
Question
3. In Drosophila, the genes sr (stripe thorax) and e (ebony body) are 8 m.u. apart on chromosome 3 and are recessive to wild type. A striped female homozygous for wild type body was crossed with an ebony male homozygous for wild type thorax. All of the offspring were phenotypically wild type. a. (8 points) What kind of gametes will be produced by the Fi females, and in what proportions? (8 points) What kind of gametes will be produced by the Fi males, and in what proportions? (in Drosophila, there is no crossing over in males) b.Explanation / Answer
A. Parent srsrEE X SSee
F1 SsrEe
A. sr--------E
S---------e
Gametes sr--------E Stripe Normal Body - 1/4
S---------e Normal Thorax and Ebony - 1/4
sr--------e Stripe and ebony - 1/4
S--------E Wild type - 1/4
B. Male No crossing over
Gametes sr--------E Stripe Normal Body - 1/2
S---------e Normal Thorax and Ebony - 1/2
C. F1 female cross with Ebony stripe male
The offsprings are
sr--------e Male
1. sr------------E sr------------E / sr--------e Stripe Normal body 1/4
2. S--------------e S--------------e / sr-----------e Normal thorax ebony 1/4
3. sr-------------e sr-------------e / sr----------e Stripe ebony 1/4
4. S--------------E S---------------E / sr---------e Wild type 1/4
D. F1 female cross with F1 Male
Male has 2 gametes. @ possiblies will be there.
sr--------E Male
1. sr------------E sr------------E / sr--------E Stripe Normal body
2. S--------------e S--------------e / sr-----------E Wild type
3. sr-------------e sr-------------e / sr----------E Stripe Normal Body
4. S--------------E S---------------E / sr---------E Wild type
Other possibility
S--------e Male
1. sr------------E sr------------E / S--------e Wild type
2. S--------------e S--------------e / S-----------e Normal thorax ebony
3. sr-------------e sr-------------e / S----------e Normal thorax ebony
4. S--------------E S---------------E / S---------e Wild type
Normal thorax ebony 1/2 and Wild type 1/2
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