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. Diagram this cross, showing the genotypes and phenotypes.

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, meaning that only one copy of the black allele is needed for the phenotype to be expressed.

Genotype and Phenotype

The genotype is the genetic makeup of an organism, represented by alleles (e.g., BB for black, Bb for black, and bb for white). The phenotype is the observable characteristic resulting from the genotype. In this cross, the F₁ generation has a genotype of Bb, resulting in a black phenotype, while the F₂ generation shows a phenotypic ratio of 3:1 due to the segregation of alleles.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. It helps visualize the combination of alleles from each parent. For this guinea pig cross, a Punnett square can be constructed to show the F₁ generation's genotype (Bb) and the resulting F₂ generation's genotypes (BB, Bb, bb), illustrating the expected 3:1 phenotypic ratio.