Question

and long). thus, each gamete will contain one of the coat - color alleles, c or c and one of the hair - length alleles, b or b. in repeated crosses of a specific dark, short - haired dog with an albino, long - haired dog, all the offspring were dark with short hair, as shown in cross i. however, in subsequent crosses of another dark, short - haired dog with a dark, long - haired dog, the ratios shown in cross ii below were obtained.

cross | parents | offspring
--- | --- | ---
i | dark, short hair x albino, long hair | all dark, short hair
ii | dark, short hair x dark, long hair | 3 dark, short hair; 3 dark, long hair; 1 albino, short hair; 1 albino, long hair

which of the following correctly describes the relationship of the dark - coat - color allele to the albino condition?

• it is dominant.
• it is recessive.
• it is codominant.
• it is a polygenic inheritance pattern.
• the alleles are linked.

Explanation:

In Cross I, a dark, short - haired dog is crossed with an albino, long - haired dog, and all offspring are dark with short hair. This shows that the dark - coat - color allele masks the albino allele (since all offspring show the dark phenotype), and the short - hair allele masks the long - hair allele. In dominant inheritance, a dominant allele is expressed in the phenotype when present (even in heterozygous form), and it masks the recessive allele. Here, the dark - coat - color allele is expressed in the offspring while the albino allele is not, indicating that dark - coat - color is dominant over albino. Codominance would show both traits, polygenic inheritance involves multiple genes (not indicated here), recessive would mean the allele is only expressed in homozygous form (but here dark is expressed over albino), and linked alleles refer to genes on the same chromosome (not related to dominance here).

Answer:

It is dominant.