2. (5 points) In the fruitfly, very dark (ebony) body color is determined by the

Question

2. (5 points) In the fruitfly, very dark (ebony) body color is determined by the recessive e allele. Th e+ allel e produces a normal, wild-type, honey colored body. In heterozygotes, a dark marking led a trident can be seen on the thorax of the body but otherwise the body is honey-colored. a. What kind of inheritance would produce this trident marking? b. When female es e flies are crossed to male ere files, what is the probability that the progeny will have the trident marking? A second gene D, when homozygous recessive, can produce a white colored trident marking in those flies capable of making a trident marking. When two heterozygotes for these two genes are crossed, how many white trident flies are produced? How many of the resulting flies would have a dark trident marking? c. d.

Explanation / Answer

a) The trident marking is a result of incomplete dominance of e+ over e.

b) Parents : e+e x e+e

Gametes : e+ , e & e+ , e

F1 ratio - 1/4 e+e+ : 2/4 e+e : 1/4 ee

Probability of trident marking (e+e) = 1/2 or 50%

c) Parents - Dd/e+e x Dd/e+e

Gametes - D/e+ , D/e , d/e+ , d/e and  D/e+ , D/e , d/e+ , d/e

F1 -

DD/e+e

DARK TRIDENT

Dd/e+e

DARK TRIDENT

DD/e+e

DARK TRIDENT

Dd/e+e

DARK TRIDENT

Dd/e+e

DARK TRIDENT

dd/e+e

white trident

Dd/e+e

DARK TRIDENT

dd/e+e

white trident

Genotype of white trident flies will be dd/e+e

Probability (of white trident flies) = 2/16 or 1/8

d) Proportion of flies with dark trident marking = 6/16 or 3/8.

gametes D/e+ D/e d/e+ d/e D/e+ DD/e+e+

DD/e+e

DARK TRIDENT

Dd/e+e+

Dd/e+e

DARK TRIDENT

D/e

DD/e+e

DARK TRIDENT

DD/ee

Dd/e+e

DARK TRIDENT

Dd/ee d/e+ Dd/e+e+

Dd/e+e

DARK TRIDENT

dd/e+e+

dd/e+e

white trident

d/e

Dd/e+e

DARK TRIDENT

Dd/ee

dd/e+e

white trident

dd/ee

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