Genetics Question: 1) (6 point question) A breeder had two different pure breedi

Question

Genetics Question:

1) (6 point question) A breeder had two different pure breeding lines of cantaloupe; one with a white fruit the other with a yellow fruit. He crosses these two together and produces a hybrid that has white fruit. When he selfs the hybrid he finds that the progeny have either white, green or yellow fruit. The ratio of the progeny fruit color he observes is 12 white : 1 yellow : 3 gree fruit. A) (3 points) A biochemist is interested in determining the pathway for pigmentation in cantaloupe. He hypothesizes potential biochemical pathways based on the 12:3:1 ratio seen by the breeder (there are others). Determine the expected phenotypes of the progeny based on the pathway shown. Then describe any epistatic interactions you see between the genes. (see a list of assumption below the table) Proposed pathway Expected phenotypes Epistatic interaction in a dihybrid cross A B aaB- B, Green |d-bb 1ColorlessColorless Yellow Colorless Green Yellow aabb- Colorless-- YellowGreen

Explanation / Answer

1) explanation: The breeder getting the 12:3:1 ratio in F2 progeny indicates that one gene is influencing the expression of the other gene, it is called as epistasis. If the phenotypes of the progeny closely observed,

If the colour of the fruit coded by two genes then, one gene masks the character of other when it is dominant the phenomenon is called dominant epistasis. It reflects the ratio of 12: 3:1

  p generation : white (WWgg) X yellow( wwGG)

F1 generation: WwGg ( all white because W gene is masking the expression of G gene) F2 generation: WwGg= white =9

Wwgg=white =3

wwGg= green =3

wwgg= yellow =1

the phenotypic ratio will be 12( white): 3(yellow): 1(green). Here W gene when in dominant state masking the expression of the G gene. G gene only expresses its phenotype when w is recessive, WwGg and Wwgg genotypes showing indifferent phenotypes.

A)

A-B- white

A-bb white

aaB- green

aabb-yellow

ratio= 12:3:1

A-B- white

A-bb white

aaB- yellow

aabb green

ratio=12: 3:1

A-B- white

A-bb=white

aaB-green

aabb=yellow

Expected phenotypes epistatic interaction 1 A enzyme inhibiting the colour production, so colured phenotype only produced when A enzyme gene is ressesive

A-B- white

A-bb white

aaB- green

aabb-yellow

ratio= 12:3:1

dominat epistasis 2 A enzyme inhibiting colour production and B producing green to yellow colour

A-B- white

A-bb white

aaB- yellow

aabb green

ratio=12: 3:1

Dominant epistasis 3 A enzyme inhibiting the colour production and B enzyme producing the yellow to green colour

A-B- white

A-bb=white

aaB-green

aabb=yellow

dominant epistasis

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