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)?

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

RR

RRRRR

rRrRr

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)

Rr

RRRRr

rRrrr

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)

XrYr

XrXr XrXr Yr

XrXr XrXr 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

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

RR

RRRRR

rRrRr

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)

Rr

RRRRr

rRrrr

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)

XrYr

XrXr XrXr Yr

XrXr XrXr 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

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