In a type of parakeet known as a "budgie," feather color is controlled by two genes. A yellow pigment is synthesized under the control of a dominant allele Y. Budgies that are homozygous for the recessive y allele do not synthesize yellow pigment. At an independently assorting gene, the dominant allele B directs synthesis of a blue pigment. Recessive homozygotes with the bb genotype do not produce blue pigment. Budgies that produce both yellow and blue pigments have green feathers; those that produce only yellow pigment or only blue pigment have yellow or blue feathers, respectively; and budgies that produce neither pigment are white (albino).
b. A cross is made between a pure-breeding green budgie and a pure-breeding albino budgie. What are the genotypes of the parent birds?

Verified step by step guidance

1. Step 1: Understand the genetic basis of feather color in budgies. The Y gene controls yellow pigment production, with Y being dominant and y being recessive. The B gene controls blue pigment production, with B being dominant and b being recessive. Green feathers result from the presence of both yellow and blue pigments (Y_B_), yellow feathers result from yellow pigment only (Y_bb), blue feathers result from blue pigment only (yyB_), and white feathers result from the absence of both pigments (yybb).
2. Step 2: Identify the phenotypes of the parent birds. A pure-breeding green budgie must produce both yellow and blue pigments, meaning its genotype must include dominant alleles for both Y and B. A pure-breeding albino budgie produces neither pigment, meaning its genotype must be homozygous recessive for both genes.
3. Step 3: Determine the genotype of the pure-breeding green budgie. Since it is pure-breeding, it must be homozygous for the dominant alleles of both genes. Therefore, its genotype is YYBB.
4. Step 4: Determine the genotype of the pure-breeding albino budgie. Since it is pure-breeding and albino, it must be homozygous recessive for both genes. Therefore, its genotype is yybb.
5. Step 5: Conclude that the genotypes of the parent birds are YYBB for the green budgie and yybb for the albino budgie. These genotypes will be used to predict the offspring's genotypes and phenotypes in subsequent steps.

Key Concepts

Alleles and Genotypes

Alleles are different forms of a gene that can exist at a specific locus on a chromosome. In this context, the dominant alleles Y and B control the synthesis of yellow and blue pigments, respectively, while the recessive alleles y and b do not. The genotype refers to the specific combination of alleles an organism possesses, which determines its traits. Understanding how these alleles interact is crucial for predicting the offspring's phenotypes.

Dominance and Recessiveness

In genetics, dominance refers to the relationship between alleles, where a dominant allele can mask the effect of a recessive allele in a heterozygous individual. In the case of budgies, the yellow pigment is produced by the dominant Y allele, while the recessive y allele results in no yellow pigment. Similarly, the B allele is dominant for blue pigment, while bb individuals do not produce blue. This concept is essential for determining the phenotypes of the offspring based on the parental genotypes.

Independent Assortment

Independent assortment is a principle of genetics that states that alleles for different traits segregate independently of one another during gamete formation. In this scenario, the genes controlling feather color in budgies assort independently, meaning the inheritance of yellow pigment (Y/y) does not affect the inheritance of blue pigment (B/b). This principle allows for a variety of combinations in the offspring, making it possible to predict the genotypes and phenotypes resulting from the cross between a green budgie and an albino budgie.