Question

1. cross #2: yellow vs. gray rats

a purebred yellow - haired rat is crossed with a purebred gray - haired rat. yellow hair (y) is dominant to gray (y).
a. write the parent genotypes: ____________×____________
b. complete the punnett square:
c. what percentage of offspring have yellow hair? → ______%
d. what percentage have gray hair? → ______%
e. what is the genotypic ratio? → ____________________ (bonus point)
f. what is the phenotypic ratio? → ____________________ (bonus point)

1. cross #3: scarlet vs. white roses

a heterozygous scarlet rose is crossed with a homozygous white rose. scarlet (s) is dominant over white (s).
a. write the parent genotypes: ____________×____________
b. complete the punnett square:
c. what percentage of offspring are scarlet? → ______%
d. what percentage are white? → ______%
e. what is the phenotypic ratio? → ____________________ (bonus)

Explanation:

Cross #2: Yellow vs. Gray Rats

Step1: Determine parent genotypes

Since yellow - haired rat is purebred and yellow (Y) is dominant, its genotype is YY. Gray - haired rat is purebred, so its genotype is yy.

Step2: Set up Punnett square

	Y	Y
y	Yy	Yy

Step3: Calculate percentage of yellow - haired offspring

All offspring have the genotype Yy, so 100% have yellow hair.

Step4: Calculate percentage of gray - haired offspring

Since no offspring have the genotype yy, 0% have gray hair.

Step5: Determine genotypic ratio

All offspring are Yy, so the genotypic ratio is Yy:Yy:Yy:Yy = 1:0:0:0 (or simply all Yy).

Step6: Determine phenotypic ratio

All offspring have yellow hair, so the phenotypic ratio is yellow:gray = 4:0 or 1:0.

Step1: Determine parent genotypes

A heterozygous scarlet rose has the genotype Ss and a homozygous white rose has the genotype ss.

Step2: Set up Punnett square

	S	s
s	Ss	ss

Step3: Calculate percentage of scarlet - flowered offspring

Half of the offspring have the genotype Ss (scarlet), so 50% are scarlet.

Step4: Calculate percentage of white - flowered offspring

Half of the offspring have the genotype ss (white), so 50% are white.

Step5: Determine phenotypic ratio

The phenotypic ratio of scarlet:white is 1:1.

Answer:

a. YY × yy
b.

	Y	Y
y	Yy	Yy

c. 100
d. 0
e. Yy:0:0:0
f. 1:0

Cross #3: Scarlet vs. White Roses