Question

chapter 10: dihybrid cross worksheet
in rabbits, gray hair is dominant to white hair. also in rabbits, black eyes are dominant to red eyes. these letters represent the genotypes of the rabbits:
gg = gray hair
gg = gray hair
gg = white hair
bb = black eyes
bb = black eyes
bb = red eyes

1. what are the phenotypes (descriptions) of rabbits that have the following genotypes?

ggbb _____________ ggbb _____________
ggbb _____________ ggbb _____________

1. a male rabbit with the genotype ggbb is crossed with a female rabbit with the genotype ggbb the square is set up below. fill it out and determine the phenotypes and proportions in the offspring.

how many out of 16 have gray fur and black eyes? ________
how many out of 16 have gray fur and red eyes? ________
how many out of 16 have white fur and black eyes? ________
how many out of 16 have white fur and red eyes________

1. a male rabbit with the genotype ggbb is crossed with a female rabbit with the genotype ggbb the square is set up below. fill it out and determine the phenotypes and proportions of offspring

how many out of 16 have gray fur and black eyes? ________
how many out of 16 have gray fur and red eyes? ________
how many out of 16 have white fur and black eyes? ________
how many out of 16 have white fur and red eyes? ________

Explanation:

Step1: Match genotypes to phenotypes (Q1)

Use dominant/recessive trait rules:

• $Ggbb$: Gray hair (Gg), red eyes (bb)
• $ggBB$: White hair (gg), black eyes (BB)
• $ggbb$: White hair (gg), red eyes (bb)
• $GgBb$: Gray hair (Gg), black eyes (Bb)

Step2: Fill Punnett Square (Q2)

Male gametes: $Gb$, $Gb$, $Gb$, $Gb$
Female gametes: $gB$, $gB$, $gb$, $gb$
Offspring genotypes:

	Gb	Gb	Gb	Gb
gB	$GgBb$	$GgBb$	$GgBb$	$GgBb$
gb	$Ggbb$	$Ggbb$	$Ggbb$	$Ggbb$
gb	$Ggbb$	$Ggbb$	$Ggbb$	$Ggbb$

Count phenotypes:

• Gray fur + black eyes: 8 out of 16
• Gray fur + red eyes: 8 out of 16
• White fur + black eyes: 0 out of 16
• White fur + red eyes: 0 out of 16

Step3: Fill Punnett Square (Q3)

Male/female gametes: $GB$, $Gb$, $gB$, $gb$
Offspring genotypes:

	GB	Gb	gB	gb
Gb	$GGBb$	$GGbb$	$GgBb$	$Ggbb$
gB	$GgBB$	$GgBb$	$ggBB$	$ggBb$
gb	$GgBb$	$Ggbb$	$ggBb$	$ggbb$

Count phenotypes:

• Gray fur + black eyes: 9 out of 16
• Gray fur + red eyes: 3 out of 16
• White fur + black eyes: 3 out of 16
• White fur + red eyes: 1 out of 16

Answer:

1.

• $Ggbb$: Gray hair, red eyes
• $ggBB$: White hair, black eyes
• $ggbb$: White hair, red eyes
• $GgBb$: Gray hair, black eyes

2.

• Gray fur and black eyes: 8
• Gray fur and red eyes: 8
• White fur and black eyes: 0
• White fur and red eyes: 0

3.

• Gray fur and black eyes: 9
• Gray fur and red eyes: 3
• White fur and black eyes: 3
• White fur and red eyes: 1