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In genetics, alleles are different versions of a gene that determine various traits.
These alleles can either be dominant or recessive.

Dominant alleles are represented by an uppercase letter (e.g., B for blue petal color in primroses) and can mask the presence of a recessive allele when both are present.
Recessive alleles, on the other hand, are represented by a lowercase letter (e.g., b for white petal color) and only express their trait when paired with another recessive allele.
For example, in primroses, having at least one B allele will result in blue petals, making blue the dominant color.
However, if an organism carries two recessive b alleles, it will have white petals.
Understanding the interaction between dominant and recessive alleles is crucial for predicting the outcomes of different genetic crosses and traits shown in offspring.

A genetic cross involves breeding two organisms to study how specific traits are inherited.
By examining the offspring's traits, we can determine the patterns of inheritance and the function of different genes.

In the provided exercise, a genetic cross is performed between a true-breed blue primrose (BB) and a white primrose (bb).
Normally, we'd expect all offspring to have blue petals due to the presence of at least one dominant B allele.
However, in this case, the progeny all have white petals.
This unexpected result indicates that another factor, specifically a second gene at a different locus, is interfering with the expression of the blue color.

Gene interaction occurs when the effect of one gene is modified by one or more other genes.
This can lead to various genetic phenomena, including epistasis.

Epistasis specifically refers to a situation where one gene can mask or alter the expression of another gene.
In the example with primroses, the second gene prevents the expression of the blue petal color by interfering with the dominant B allele.
This second gene acts epistatically, causing all progeny to exhibit the white petal phenotype even when they carry the dominant blue allele.
Understanding gene interaction helps explain complex inheritance patterns and can reveal much about how different traits are controlled and expressed in organisms.