In a species of mice, brown fur color is dominant to white fur color. when a brown mouse is crossed with a white mouse all of their offspring have brown fur. why did none of the offspring have white fur?

Because white fur is determined by a resessive allele. Resessive alleles are only expressed if they pair with another resessive allele.

Explanation:

The physical characteristics of the mice shown in the above question are determined by the dominance relationship between the genetic alleles. As we can see from reading the question, brown fur is a trait regulated by a dominant allele, in mice, on the other hand, white fur are a trait regulated by recessive alleles.

Dominant alleles are so named because certain genetic traits prevail over others. This is because dominant genes do not need their dominant allele pair on the chromosome, that is, they do not need to be double-dose in the genotype to manifest. However, recessive alleles are so named because to manifest their hereditary characters one must present a double dose in the genetic code.

In this way, we can define the reason that prevented the offspring, shown in the above question, from presenting white fur. Because white fur is recessive, it would require both parents to have white fur for this trait to be passed on to their offspring.

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he forelimbs below belong to four species that descended in a direct line from the ancestral mammal shown above. of the four descendants shown, which species most likely appeared earliest in evolutionary history?