The drosophila alleles for purple eyes (instead of red) and dumpy wings (instead

Question

The drosophila alleles for purple eyes (instead of red) and dumpy wings (instead of normal) are both recessive. Gene E designates eye color (E: dominant, e: recessive), and gene D designates wing shape (D: dominant, d: recessive). You cross a pure breeding purple eyes, normal winged fly to a true breeding red eyed, dumpy winged fly.
11. You cross these F1 offspring to flies that are pure breeding for purple eyes and dumpy wings. You get 200 offspring. 45 are purple eyes and dumpy winged, 43 are red eyed and normal winged, 63 are purple eyed and normal winged, and 49 are red eyed and dumpy winged. You think that these two genes could be on different chromosomes but your friend tells you that he thinks they are linked and that they are close enough to each other to have a frequency of recombinant a of 0.38. If you are correct and they are on different chromosomes, how many purple eyes, normal winged flies would you ideally expect out of your 200 offspring?
12. If your friend is correct and the genes are linked with frequency of recombinant a of 0.38 how many purple eyed, normal winged flies would you expect?
13. Calculate the chi squared value of the genes are on different chromosomes.
14. Calculate the chi squared value if your friend is correct.
15. Who is more likely to be correct? The drosophila alleles for purple eyes (instead of red) and dumpy wings (instead of normal) are both recessive. Gene E designates eye color (E: dominant, e: recessive), and gene D designates wing shape (D: dominant, d: recessive). You cross a pure breeding purple eyes, normal winged fly to a true breeding red eyed, dumpy winged fly.
11. You cross these F1 offspring to flies that are pure breeding for purple eyes and dumpy wings. You get 200 offspring. 45 are purple eyes and dumpy winged, 43 are red eyed and normal winged, 63 are purple eyed and normal winged, and 49 are red eyed and dumpy winged. You think that these two genes could be on different chromosomes but your friend tells you that he thinks they are linked and that they are close enough to each other to have a frequency of recombinant a of 0.38. If you are correct and they are on different chromosomes, how many purple eyes, normal winged flies would you ideally expect out of your 200 offspring?
12. If your friend is correct and the genes are linked with frequency of recombinant a of 0.38 how many purple eyed, normal winged flies would you expect?
13. Calculate the chi squared value of the genes are on different chromosomes.
14. Calculate the chi squared value if your friend is correct.
15. Who is more likely to be correct?
11. You cross these F1 offspring to flies that are pure breeding for purple eyes and dumpy wings. You get 200 offspring. 45 are purple eyes and dumpy winged, 43 are red eyed and normal winged, 63 are purple eyed and normal winged, and 49 are red eyed and dumpy winged. You think that these two genes could be on different chromosomes but your friend tells you that he thinks they are linked and that they are close enough to each other to have a frequency of recombinant a of 0.38. If you are correct and they are on different chromosomes, how many purple eyes, normal winged flies would you ideally expect out of your 200 offspring?
12. If your friend is correct and the genes are linked with frequency of recombinant a of 0.38 how many purple eyed, normal winged flies would you expect?
13. Calculate the chi squared value of the genes are on different chromosomes.
14. Calculate the chi squared value if your friend is correct.
15. Who is more likely to be correct?

Explanation / Answer

11. F1 offspring crossed with purple eyes and dumpy wings

EeDd x eedd

ED

Ed

eD

ed

ed

EeDd( red eyed normal wing)

Eedd(red eyed dumpy wing)

eeDd(purple eyed normal wing)

eedd(purple eyed dumpy wing)

observed number

43

49

63

45

If the genes are on different chromosome the expected purple eyed normal winged flies would be 1/4*200=50 as the ratio of the offsprings then would have been 1:1:1:1

12. If my friend is correct i.e the genes are linked then the expected value of purple eyed normal wing would be 9/16*200=113(rounded to whole number)

13. Chi square if the genes are on different chromosome

Null hypothesis: 1:1:1:1

observed(o)

expected(e)

o-e

(o-e)2

(o-e)2/e

X2

45

1/4*200=50

-5

25

0.5

4.88

43

1/4*200=50

-7

49

0.98

63

1/4*200=50

13

169

3.38

49

1/4*200=50

-1

1

0.02

degree of freedom:4-1=3

conclusion:the calculated X2 value is 4.88 which is less than the tabulated value(7.82) at df 3 and 5% level of significance.so null hypothesis is accepted.

14. Chi square if the genes are on same chromosome

Null hypothesis: 9:3:3:1

observed(o)

expected(e)

o-e

(o-e)2

(o-e)2/e

X2

63

9/16*200=112.5

49.5

2450.25

21.78

101.22

49

3/16*200=37.5

-11.5

132.25

3.52

45

3/16*200=37.5

-7.5

56.25

1.5

43

1/16*200=12.5

-30.5

930.25

74.42

Degree of freedom:4-1=3

Conclusion: the calculated value of X2 is 101.22 which is more than the tabulated value (7.82) at df 3 and 5% level of significance.so null hypothesis is rejected

15. The genes are present on different chromosome as we can conclude by the X2 values. So the friend is wrong.

ED

Ed

eD

ed

ed

EeDd( red eyed normal wing)

Eedd(red eyed dumpy wing)

eeDd(purple eyed normal wing)

eedd(purple eyed dumpy wing)

observed number

43

49

63

45

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