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. What will the offspring be like if two F₂ white guinea pigs are mated?

Verified step by step guidance

1. Determine the inheritance pattern: The problem suggests a Mendelian inheritance pattern with black (B) being dominant and white (b) being recessive. This means black guinea pigs can have genotypes BB or Bb, while white guinea pigs must have the genotype bb.
2. Analyze the F₂ generation: The 3:1 ratio in the F₂ generation indicates a monohybrid cross (Bb x Bb), where the genotypes are distributed as 1 BB : 2 Bb : 1 bb. Only the bb individuals are white.
3. Identify the genotypes of the parents for this specific cross: Since the question asks about mating two F₂ white guinea pigs, both parents must have the genotype bb.
4. Set up the Punnett square for the bb x bb cross: Each parent can only contribute the recessive allele (b) to their offspring. Fill in the Punnett square to determine the genotypes of the offspring.
5. Interpret the results: Since both parents are bb, all offspring will inherit one b allele from each parent, resulting in 100% bb offspring. This means all the offspring will be white guinea pigs.

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, black fur is dominant over white fur, meaning that when a black and a white guinea pig are crossed, the offspring (F₁ generation) will exhibit the dominant trait, resulting in all black guinea pigs.

Genotype and Phenotype

The genotype is the genetic makeup of an organism, while the phenotype is the observable physical characteristics. In the F₂ generation, the phenotypic ratio of 3:1 (black to white) suggests that the black guinea pigs can be either homozygous (BB) or heterozygous (Bb), while the white guinea pigs must be homozygous recessive (bb).

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two organisms. When two F₂ white guinea pigs (bb) are mated, the Punnett square will show that all offspring will also be white (bb), as there are no dominant alleles present to express the black phenotype.