How was Mendel able to derive postulates concerning the behavior of 'unit factors' during gamete formation when he could not directly observe them?

How do we know whether an organism expressing a dominant trait is homozygous or heterozygous?

In analyzing genetic data, how do we know whether deviation from the expected ratio is due to chance rather than to another, independent factor?

Since experimental crosses are not performed in humans, how do we know how traits are inherited?

Write a short essay that correlates Mendel's four postulates with what is now known about genes, alleles, and homologous chromosomes.

In a cross between a black and a white guinea pig, all members of the F₁ generation are black. The F₂ generation is made up of approximately 3/4 black and 1/4 white guinea pigs. Diagram this cross, showing the genotypes and phenotypes.

Albinism in humans is inherited as a simple recessive trait. For the following families, determine the genotypes of the parents and offspring. (When two alternative genotypes are possible, list both.)

Two normal parents have five children, four normal and one albino.