Question

Use your knowledge of Mendelian genetics to write a hypothesis that answers the lab question, “What is the effect of the genes of the parental mice on the fur color of the offspring mice?” Be sure to use the “If . . . then . . . ” format.

Answer 1

Answer:

In Mendelian genetics allele of each gene from parent will segregate from each other so the gametes only carry one each .

If the parental mice has two different fur colour( white or black )

the colour of offspring ' s fur either would be black and white or the combination of both grey

Answer 2

Answer:

If the phenotypic ratio is found to be 3:1 in the F₂ generation, then regarding the fur color, the color which is expressed resembles the parent mice shows dominance over the color which fails to express itself.

Explanation:

Assuming that in mice,

• The fur color black (B) is governed by the B gene and white is governed by the b gene. And Black fur is dominant over white fur color.

• If the first generation of the offspring from the heterozygous mice exhibits the ratio of 3:1, then the allele for black fur color(B) is dominant over the allele of white fur color (b).

• According to the Mendelian law of dominance, when a pair of allelomorphic characters or alleles are present together, only one of them expresses itself and the other remains hidden. The character which is expressed or visible is dominant and the other is recessive.

• So while experimenting with homozygous mice,

We can expect :

parent P:   BB (Black) × (white) bb

                           ↓                ↓

Gametes:            B       ×         b

                                    ↓

F₁ generation:             Bb × Bb

            (heterozygous Black) on selfing

                                             ↓

F₁ gametes:   B,   b,   B,     b

F₂ generation: BB  Bb   bB  bb

BB - homozygous black mice

Bb - Heterozygous black mice

bB - Heterozygous black mice

bb - Homozygous white mice

Thus the genotypic ratio is 1:2:1

and the phenotypic ratio: 3:1

• A cross between two individuals that differ in only a pair of contrasting characters is called a monohybrid cross. In a hybrid where both the characters are present, only one expresses itself called dominant while the other remains suppressed is called recessive in F₁ generation. F₂ generation expresses both the characters in a 3:1 phenotypic ratio in a monohybrid cross.