Question

Mendel crossed peas having round seeds and yellow cotyledons (seed leaves) with peas having wrinkled seeds and green cotyledons. All the F1 plants had round seeds with yellow cotyledons. Based on this cross, what is the probability that an organism in the F2 generation will have round seeds and green cotyledons and NOT be true breeding? (Hint: Think carefully about what true breeding means in terms of genotype.)

Answer 1

let the alleles be R- round seeds, r- wrinkled seeds

Y- yellow cotyledon and y - green cotyledon

so RRYY* rryy

RrYy ( F1 plants)

RrYy * RrYy

	RY	Ry	rY	ry
RY	RRYY	RRYy	RrYY	RrYy
Ry	RRYy	RRyy ( round green)	RrYy	Rryy ( round, green)
rY	RrYY	RrYy	rrYY	rrYy
ry	RrYy	Rryy (round, green)	rrYy	rryy

out of 16 possible genotypes 3 shows Round, green phenotype so among this RRyy is true breeding for both Round seeds and green cotyledon other 2 are not true breeding for Round seeds but are true breeding for green cotyledon, since green is recessive phenotype only yy can show green phenotype so taking both traits Rryy is not true breeding so probability of round sedds and green cotyledons in F2=2/16

=1/8

( true breeding means it will continue to give same phenotype for generations that is RRyy, RRYY, rryy)