Question

1. Mendel crossed peas with round, green seeds with peas having wrinkled, yellow seeds. 100% of the F₁ plants had seeds that were round and yellow.
Predict the results of test-crossing these F₁ plants.

a. 3/4 round, yellow; 1/4 wrinkled, green
b.		9/16 round, yellow; 3/16 round, green; 3/16 wrinkled, yellow; 1/16 wrinkled, green
c.		1/2 round, yellow; 1/2 wrinkled, green
d.		1/4 round, yellow; 1/4 round, green; 1/4 wrinkled, yellow; 1/4 wrinkled, green
e.		None of the Above

2.

Identical twins are produced from the same sperm and egg (which splits after the first mitotic division), whereas fraternal twins are produced from separate sperm and separate egg cells. If two parents, one with brown eyes (a dominant trait) and the other with blue eyes (the recessive trait) produce one twin boy with blue eyes, what is the probability that a fraternal twin will transmit the blue eye allele to his or her offspring? Answer as decimal

Answer 1

1)

Option (c) is correct. The results of test crossing these F1 plants will be 1/ 4 round, yellow; 1/4 round, green; 1/4 wrinkled, yellow; 1/4 wrinkled, green.

Test crossing is breeding of an individual with an individual having recessive phenotype.

Test crossing F1 Generation:

	RY	Ry	rY	ry
ry	RrYy	Rryy	rrYy	rryy
ry	RrYy	Rryy	rrYy	rryy
ry	RrYy	Rryy	rrYy	rryy
ry	RrYy	Rryy	rrYy	rryy

RY - Round yellow

Ry - Round green

rY -  wrinkled, yellow

ry -  wrinkled, green

2)

Probability that a fraternal twin will transmit the blue eye allele to his or her offspring = 0.25

As the brown eyes are dominant trait. Let "B" indicate allele controlling brown eye color, and "b" controlling blue eye color.

As offspring produced have blue eyes, it means genotype of mother with brown eyes is heterozygous i.e. "Bb", while genotype of father with blue eyes is "bb".

So two type of gametes would be produced by mother are "B" and "b", while father produces "b" gamete.

Probability of getting offspring with blue eyes = 1/2

And as father produces two types of gametes with X chromosome and Y chromosome so probability of producing boy is 1/2

So net probability that fraternal twins would be produced with blue eyes is 1/4 or 0.25

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