Question

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Assignment: Using Punnett Squares Exploration

First Cross





















Genotypic ratio:
Phenotypic ratio:


Second Cross





















Genotypic ratio:
Phenotypic ratio:
Third Cross





















Genotypic ratio:
Phenotypic ratio:



Questions
1. What conclusions can you draw about the results of your first cross between a homozygous red bull (RR) and a heterozygous red cow (Rr)?






2. What conclusions can you draw about the results of your second cross between a heterozygous red bull (Rr) and a heterozygous red cow (Rr)?






3. What conclusions can you draw about the results of your third cross between a homozygous white bull (rr) and a homozygous white cow (rr)?

Answer 1

a)





Therefore:Crossing results in 50% (dominant homozygote) and 50% (dominant heterozygote).
b)





Therefore:Crossing results in 25% (dominant homozygote), 50% (dominant heterozygote) and 25% (homozygous recessive).
c)





Therefore:Crossing results in 100% (homozygous recessive).

Answer 2

a)

R R

R RR RR

r Rr Rr

Genotypic ratio: RR : Rr = 2 : 2 = 1: 1

Phenotypic ratio: homozygous red bull (RR) : heterozygous red cow (Rr) = 2:2 = 1: 1

b)

R r

R RR Rr

r Rr rr

Genotypic ratio: RR : Rr:rr = 1:2:1

Phenotypic ratio: homozygous red bull (RR) : heterozygous red cow (Rr) : homozygous white bull (rr) = 1: 2: 1

c)

Xr Yr

Xr Xr Xr Xr Yr

Xr Xr Xr Xr Yr

Genotypic ratio: Xr Xr: Xr Yr = 2: 2 = 1: 1

Phenotypic ratio: homozygous white cow (Xr Yr) : heterozygous white bull (Xr Yr) = 2: 2 = 1: 1

Step-by-step explanation:

a)

First cross is between a a homozygous red bull (RR) and a heterozygous red cow (Rr)

This shows that "Red" color is a dominant trait

So the cross between Rr and RR is

R R

R RR RR

r Rr Rr

Genotypic ratio: RR : Rr = 2 : 2 = 1: 1

Phenotypic ratio: homozygous red bull (RR) : heterozygous red cow (Rr) = 2:2 = 1: 1

b)

Cross between a heterozygous red bull (Rr) and a heterozygous red cow (Rr)

R r

R RR Rr

r Rr rr

Genotypic ratio: RR : Rr:rr = 1:2:1

Phenotypic ratio: homozygous red bull (RR) : heterozygous red cow (Rr) : homozygous white bull (rr) = 1: 2: 1

c)

Cross between a homozygous white bull (rr) and a homozygous white cow (rr)

Xr Yr

Xr Xr Xr Xr Yr

Xr Xr Xr Xr Yr

Genotypic ratio: Xr Xr: Xr Yr = 2: 2 = 1: 1

Phenotypic ratio: homozygous white cow (Xr Yr) : heterozygous white bull (Xr Yr) = 2: 2 = 1: 1