Question

A recessive allele in mice produces offspring that are primarily yellow in color. Unfortunately, there are other complications during gestation and not all embryos survive to birth. A breeder has a large population of heterozygous mice she breeds together and gets 138 tan (normal) mice and 19 yellow ones. What percentage of homozygous mice died before they were born? Show work and explain please.

Answer 1

In a monohybrid cross when F₁individuals are self fertilized, we get F₂generation in the ratio of 3 dominant and 1 recessive. In the given case the breeder has got 138 normal mice. It means 138 represents figure 3 of 3:1ratio.

Since, we will have to calculate total size of F₂ generation, we will divide 138 by 3 to know what 1part out of 3 parts equals

As such we get 138/3=46

Since total size of the 3:1, i-e, 4 parts: which equals 46*4=184

Out of 184, 3 parts i-e 184*3/4=138 are normal and 1/4*184=46 should be recessive.

But we see that only 19 recessive individuals have survived out of 46, that means 27 have died, that constitutes 58% of the recessive population.