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A litter of mice from the mating of two agouti black parents includes offspring with the following fur colors:

solid color, black

solid color, brown (sometimes called chocolate)

agouti black

agouti brown (sometimes called cinnamon)

What would be the expected frequency of agouti brown offspring in the litter?
none

1/8

3/16

1/4

1/2

9/16

not enough information given

Respuesta :

Answer:

3/16

Explanation:

Given:

Parents are;

both parents are Agouti black and agouti black ( AaBb);

Black is dominant on brown (B over b);

Agouti is dominant on solid color ( A over a);

So, progeny are  

(AABB, AaBb, AABb, AaBB, Aabb, aaBB, aaBb aabb  so on )

Here 3 out of 16 progeny are agouti brown ( genotype AAbb, Aabb);

So,expected frequency of agouti brown offspring in the litter= 3/16.

The correct answer is explained below:

Explanation:

  • Fur characteristics in mice can be determined by two separate genes which are not linked to each other.
  • One gene determines the bands of pigmentation in fur.The Agouti fur is dominant over the solid fur.
  • Let Agouti be represented by A allele and solid fur be represented by a allele.
  • The other gene determines the pigment in the color of the fur. The black pigment is dominant over the brown pigment.
  • Let black color be represented by B allele and brown color be represented by b allele.
  • In the given question two agouti black parents are crossed.
  • The genotypes of the parents can be AABB or AaBb, that is, the parents can be either homozygous or heterozygous for both the genes.
  • Among the offspring as four different phenoypes are found so we can conclude that both the parents are heterozygous for both the genes, that is,their genotypes are AaBb.
  • This is because crossing parents who are homozygous for both the genes, that is, AABB would produce offfspring of only a single genotype, that is, AaBb and phenotype, agouti and black.
  • The gametes produced by each of the AaBb parents: AB, Ab, aB, ab.
  • Crossing the parents with AaBb genotype and agouti black phenotype we get,

             AB                        Ab                        aB                         ab

AB       AABB                 AABb                    AaBB                   AaBb

 (Agouti/Black)   (Agouti/Black)     (Agouti/Black)   (Agouti/Black)

Ab       AABb                  AAbb                    AaBb                   Aabb

  (Agouti/Black) (Agouti/Brown) (Agouti/Black)  (Agouti/Brown)

aB       AaBB                   AaBb                    aaBB                    aaBb

  (Agouti/Black)     (Agouti/Black)     (Solid/Black)     (Solid/Black)

ab       AaBb                   Aabb                     aaBb                    aabb

 (Agouti/Black)   (Agouti/Brown)   (Solid/Black)     (Solid/Brown)

  • The above dihybrid cross shows the possible genotypes and phenotypes of the offspring.
  • Here, the frequency of Agouti/ Black offspring is: [tex]\frac{9}{16}[/tex].
  • The frequency of Agouti/ Brown offspring is: [tex]\frac{3}{16}[/tex].
  • The frequency of Solid/ Black offspring is: [tex]\frac{3}{16}[/tex].
  • The frequency of Solid/ Brown offspring is: [tex]\frac{1}{16}[/tex].
  • Hence, the answer to the question about the frequency of agouti brown offspring is: [tex]\frac{3}{16}[/tex].

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