If a student was working on an experimental population of pea plants. The studen

Question

If a student was working on an experimental population of pea plants. The student crossed plants that were reddish-purple and gave long pollen to other plants that were pink and gave round pollen and he wrote the genotypes of the plants in cross: R L / r l x r l / r l. (Flower colour = R=reddish-purple, r = pink) and pollen shape (L = long, r = round). Choose best option for completing sentence in his notebook. If the two loci, flower colour and pollen shape, are not linked, l would expect ____ of progeny of this cross to be R L / r l.

Options are

3, 25%, 100%, 75 %, and None .

Explanation / Answer

This is a example of dihybrid test cross. In this experiment two genes are involved flower colour (Rr) and pollan shape (Ll) thats why it is called dyhibrid cross. Each gene has 2 allele dominant (R & L) and recessive (r & l).

Cross between RRLL x rrll

F1 generation RrLl (reddish-purple flower with long pollan)

Test cross RrLl x rrll

Gametes formed RL, Rl, rL, rl x rl

F2 generation RL Rl rL rl

rl RrLl Rrll rrLl rrll

rl RrLl Rrll rrLl rrll

rl RrLl Rrll rrLl rrll

rl RrLl Rrll rrLl rrll

According to this table 4/16 progeny of this cross to be RL/rl. The ratio obtained from this cross is 1:1:1:1.

4/16 reddish-purple long

4/16 reddish-purple round

4/16 pink long

4/16 pink round

According to the low of independent assortment two allele of one gene pair seggregate independentlyof the allele of another gene pair if they are not linked. So here from the test cross you will obtained 16 progeny in which all combinations are present in equal proportion.

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