You have four guinea pigs for a genetic study. One male and one female are from a strain that is pure-breeding for short brown fur. A second male and female are from a strain that is pure-breeding for long white fur. You are asked to perform two different experiments to test the proposal that short fur is dominant to long fur and that brown is dominant to white. You may use any of the four original pure-breeding guinea pigs or any of their offspring in experimental matings. Design two different experiments (crossing different animals and using different combinations of phenotypes) to test the dominance relationships of alleles for fur length and color, and make predictions for each cross based on the proposed relationships. Anticipate that the litter size will be 12 for each mating and that female guinea pigs can produce three litters in their lifetime.

Key Concepts

Dominance in Genetics

Dominance refers to the relationship between alleles, where one allele masks the expression of another in a heterozygous individual. In this context, short fur (S) is proposed to be dominant over long fur (s), meaning that a guinea pig with at least one S allele will exhibit short fur. Similarly, brown fur (B) is suggested to be dominant over white fur (b). Understanding dominance is crucial for predicting the phenotypes of offspring in genetic crosses.

Punnett Square

A Punnett square is a diagram used to predict the genotypes and phenotypes of offspring from genetic crosses. By organizing the alleles of the parents, it allows for a visual representation of all possible combinations in the offspring. This tool is essential for analyzing the results of the proposed experiments, as it helps to determine the expected ratios of phenotypes based on the dominance relationships of the alleles involved.

Mendelian Inheritance

Mendelian inheritance is the set of principles that describe how traits are passed from parents to offspring through alleles. It includes concepts such as segregation and independent assortment. In this scenario, understanding Mendelian inheritance is vital for designing the experiments and making predictions about the offspring's fur length and color, as it provides the framework for how traits are inherited in the guinea pigs.