In rabbits, albinism is an autosomal recessive condition caused by the absence of the pigment melanin from skin and fur. Pigmentation is a dominant wild-type trait. Three pure-breeding strains of albino rabbits, identified as strains 1, 2, and 3, are crossed to one another. In the table below, F₁ and F₂ progeny are shown for each cross. Based on the available data, propose a genetic explanation for the results. As part of your answer, create genotypes for each albino strain using clearly defined symbols of your own choosing. Use your symbols to diagram each cross, giving the F₁ and F₂ genotypes. <>

Verified step by step guidance

1. Define the genetic basis of albinism in rabbits. Albinism is an autosomal recessive condition, meaning that two copies of the recessive allele are required for the albino phenotype. Use a symbol such as 'a' for the recessive allele causing albinism and 'A' for the dominant allele responsible for pigmentation.
2. Analyze the data provided for the F₁ and F₂ generations. If the F₁ progeny from a cross between two albino strains (e.g., strain 1 and strain 2) are all pigmented, this suggests that the two strains have mutations in different genes. This is an example of genetic complementation.
3. Assign genotypes to each strain based on the complementation results. For example, if strain 1 has a mutation in gene 1 and strain 2 has a mutation in gene 2, you could assign strain 1 the genotype 'aaBB' and strain 2 the genotype 'AAbb'. The F₁ progeny would then have the genotype 'AaBb', which is pigmented because they have at least one dominant allele for each gene.
4. Diagram the F₁ and F₂ crosses using the assigned genotypes. For the F₁ generation, cross the genotypes of the two parental strains (e.g., 'aaBB' × 'AAbb') to determine the F₁ genotype (e.g., 'AaBb'). For the F₂ generation, perform a Punnett square to determine the genotypic and phenotypic ratios of the offspring when the F₁ individuals are crossed (e.g., 'AaBb' × 'AaBb').
5. Interpret the F₂ results. If the F₂ generation includes albino offspring, this confirms that the mutations are in different genes. The albino offspring would have genotypes such as 'aaBB', 'AAbb', or 'aabb', depending on the specific genetic combinations resulting from the Punnett square.

Key Concepts

Autosomal Recessive Inheritance

Autosomal recessive inheritance refers to a pattern where a trait is expressed only when an individual has two copies of the recessive allele. In the case of albinism in rabbits, the absence of melanin is due to having two recessive alleles (aa). If an individual has at least one dominant allele (A), they will exhibit the wild-type phenotype, which includes pigmentation.

Genotype and Phenotype

The genotype is the genetic makeup of an organism, represented by the alleles it carries, while the phenotype is the observable physical or biochemical characteristics resulting from the genotype. For example, in the context of the rabbit strains, the genotypes of the albino rabbits would be homozygous recessive (aa), while the wild-type rabbits would have at least one dominant allele (A).

Punnett Squares and Genetic Crosses

Punnett squares are tools used to predict the genotypes of offspring from genetic crosses. By diagramming the alleles from each parent, one can visualize the potential combinations in the F₁ and F₂ generations. This method is essential for understanding inheritance patterns, especially when analyzing the results of crosses between different strains of rabbits in this scenario.