Lab Report: Genetic Crosses 1

Question

  Create a Punnett square to calculate the possible genotypes that can result from a cross between the two parent plants. In a dihybrid cross, the alleles of the gametes of each parent are written along the left side and top of the Punnett square, just as they are for a monohybrid cross. Fill in the squares with the predicted genotypes. Some information has been filled in for you to help you complete a Punnett square for a dihybrid cross.

	PPRr
PPRr
		ppRR
			pprr

Answer 1

Hi Delanie. The dihybrid cross is pretty common. It looks like this:

PpRr x PpRr

The possible genotypes for the gametes of the first parent are:

PR - Pr - pR - pr

Put those in the first row (heading) of the Punnett square.

	PR	Pr	pR	pr
		PPRr
	PPRr
			ppRR
				pprr

The genotypes for the second parent are:

PR - Pr - pR - pr

They go in the first column of the Punnett Square.

	PR	Pr	pR	pr
PR		PPRr
Pr	PPRr
pR			ppRR
pr				pprr

All that's left is to make pairs, going column by column adding up the genotypes in each row.

	PR	Pr	pR	pr
PR	PPRR	PPRr	PpRR	PpRr
Pr	PPRr	PPrr	PpRr	Pprr
pR	PpRR	PpRr	ppRR	ppRr
pr	PpRr	Pprr	ppRr	pprr

It only looks scary.