Question

In the late 1920s a mutation occured in many silver fox farms around the world. these farms that sold expensive furs were proud of the quality of their furs , and each advertised that it had the best, most pure breed of all the fox farms. The new mutations produced a "platinum" coat pattern that was commercially desirable, so the farms crossed them to get more. The results of their breeding experiments were as follows: (1) silver - silver ® all silver offspring; (2) silver - platinum ® equal numbers of silver and platinum; (3) platinum - platinum ® 2 platinum for each silver offspring. Explain.

Answer 1

Answer:

In a homozygous state, the allele "P" is lethal. Those individuals with PP genotype will be born dead.

Explanation:

The allele P is dominant over p and expresses the trait "platinum". But in the homozygous state, it is mortal, PP.  The allele p expresses the "Silver" trait.

This is:

• For platinum individuals, the genotype  should be Pp

• For silver individuals, the genotype should be pp

• For dead individuals, the genotype should be PP.

So in the crosses, the punnet squares are:

1- Silver x Silver

     Parental)          pp     x     pp

     Gametes)       p    p         p   p

     Punnet square)    

                                      p             p

                              p     pp           pp

                              p     pp           pp

     

       F1 Genotype) 100 % recessive homozygote pp

2-  Silver x Platinum

     Parental)          pp     x     Pp

     Gametes)       p    p         P   p

     Punnet square)    

                                       p             p

                              P     Pp           Pp

                              p    pp           pp

     

       F1 Genotype) 50 % recessive homozygote pp,

                              50% heterozygote for the trait Pp

3- Platinum x Platinum

     Parental)          Pp     x     Pp

     Gametes)       P    p        P   p

     Punnet square)    

                                       P             p

                              P     PP           Pp

                              p     Pp           pp

     

       F1 Genotype) 25 % recessive homozygote pp

                              50% heterozygote for the trait Pp

                              25% dominant homozygote PP. This is a dead          

                                   individual.

In this last cross, individuals with genotype PP dye, so, of the whole offspring, there are two platinum for each silver offspring.