The following is a pedigree of a fairly common human hereditary trait (those pos

Question

The following is a pedigree of a fairly common human hereditary trait (those possessing the trait are indicated by the shaded symbols).

 

a) Is the gene causing this effect dominant (R) or recessive (r)?

b) Designate the genotype of each individual in the pedigree and indicate the choice of genotypes if you think that more than one genotype is possible for a given individual.

Individual

Genotype

Individual

Genotype

I 1

 

II 3

 

I 3

 

II 4

 

I 4

 

II 5

 

II 1

 

III 1

 

II 2

 

 

 

Individual

Genotype

Individual

Genotype

I 1

 

II 3

 

I 3

 

II 4

 

I 4

 

II 5

 

II 1

 

III 1

 

II 2

 

 

 

Explanation / Answer

The trait is recessive, and from left to right the genotypes of the individuals should be: I: rr Rr/RR Rr Rr II: Rr Rr Rr Rr rr III: rr Had the trait been dominant one of the parents with an afflicted offspring would have been affected.

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