Lab Report: Genetic Crosses 1

Question

The dominant and recessive alleles for these traits are as follows:

purple flowers: P

white flowers: p

round seeds: R

wrinkled seeds: r

Genotype of parent plant 1: Pp Rr

Genotype of parent plant 2: Rr Pp

Parent plant 1

Gamete 1: PR

Gamete 2: Pr

Gamete 3: rP

Gamete 4: rp

Parent plant 2

Gamete 1: PR

Gamete 2: Pr

Gamete 3: rP

Gamete 4: rp

Part 2 Punnett Square

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

1.    Look at the Punnett square and list the genotypes that would correspond to each phenotype.

Answer:

purple flowers, round seeds:

purple flowers, wrinkled seeds:

white flowers, round seeds:

white flowers, wrinkled seeds:

2.    Finally, look at the Punnett square again and write the numbers of offspring with each phenotype.

Answer:

purple flowers, round seeds:

purple flowers, wrinkled seeds:

white flowers, round seeds:

white flowers, wrinkled seeds:

Answer 1

Hi Delanie. This problem has to do with reading the Punnett Square, and understanding genotype and phenotype on dihybrid crosses.

Let's break it down.

This information tells you what's recessive and what's dominant:

The dominant and recessive alleles for these traits are as follows:

purple flowers: P

white flowers: p

round seeds: R

wrinkled seeds: r

Remember that either PP or Pp and RR or Rr will look dominant by phenotype even though the genotypes are different. And that the only way to show the recessive phenotype is to be of the double recessive genotype (pp or rr).

The next information identifies the cross as a dihybrid cross:

Genotype of parent plant 1: Pp Rr

Genotype of parent plant 2: Rr Pp

This is the information you need to create the Punnett Square:

Parent plant 1

Gamete 1: PR

Gamete 2: Pr

Gamete 3: rP

Gamete 4: rp

Parent plant 2

Gamete 1: PR

Gamete 2: Pr

Gamete 3: rP

Gamete 4: rp

Then we read the Punnett Square to answer the next two questions:

Part 2 Punnett Square

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

1.    Look at the Punnett square and list the genotypes that would correspond to each phenotype.

Answer:

purple flowers, round seeds: PPRR or PpRr (any combination having at least one P and one R)

purple flowers, wrinkled seeds: PPrr or Pprr (any combination having at least one P and two r's)

white flowers, round seeds: ppRR or ppRr (any combination having two p's and at least one R)

white flowers, wrinkled seeds: pprr (must have two p's and two r's)

This last question is just a matter of counting the combinations listed above:

2.    Finally, look at the Punnett square again and write the numbers of offspring with each phenotype.

Answer:

purple flowers, round seeds:9

purple flowers, wrinkled seeds: 3

white flowers, round seeds:3

white flowers, wrinkled seeds: 1