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. Two different matings were made between black members of the F₂ generation, with the following results. Diagram each of the crosses. Cross Offspring _ Cross 1 All black Cross 2 3/4 black, 1/4 white

Verified step by step guidance

1. <Step 1: Understand the genetic basis of the problem. The black color is dominant over the white color in guinea pigs. Represent the black allele as 'B' and the white allele as 'b'.>
2. <Step 2: Analyze the F₁ generation. Since all F₁ offspring are black, the black parent must be homozygous dominant (BB) and the white parent homozygous recessive (bb). Thus, all F₁ offspring are heterozygous (Bb).>
3. <Step 3: Examine the F₂ generation. The F₁ heterozygous (Bb) individuals are crossed, resulting in a 3:1 phenotypic ratio in the F₂ generation, which is typical for a monohybrid cross. The genotypic ratio is 1 BB : 2 Bb : 1 bb.>
4. <Step 4: Diagram Cross 1. Since all offspring are black, the parents must both be homozygous dominant (BB). This results in all offspring being BB.>
5. <Step 5: Diagram Cross 2. The 3:1 ratio of black to white offspring suggests a typical heterozygous cross (Bb x Bb), resulting in the genotypic ratio of 1 BB : 2 Bb : 1 bb, where BB and Bb are black, and bb is white.>

Key Concepts

Mendelian Inheritance

Mendelian inheritance refers to the principles of heredity established by Gregor Mendel, which include the concepts of dominant and recessive traits. In this case, the black coat color in guinea pigs is dominant over the white coat color. This means that when a dominant allele is present, it will express the dominant phenotype, as seen in the F₁ generation where all offspring are black.

Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from a genetic cross. It helps visualize the combination of alleles from each parent. In this scenario, the Punnett square can be used to illustrate the expected ratios of black and white guinea pigs in the F₂ generation, confirming the 3:1 ratio observed.

Genotype and Phenotype

Genotype refers to the genetic makeup of an organism, while phenotype is the observable physical or biochemical characteristics. In the guinea pig example, the genotype of the black offspring could be either homozygous dominant (BB) or heterozygous (Bb), but the phenotype is consistently black. Understanding the distinction between these terms is crucial for interpreting the results of the crosses.