When Is a Dominant Allele Expressed?
Chapter 6: Fundamentals of Genetics

According to the Law of Dominance, the dominant allele is expressed in a homozygous or heterozygous condition. The recessive allele is only expressed in a homozygous condition, when there is no dominant allele present. You can model the Law of Dominance if you…

Try This

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1. Use four beans or other similar objects, two of one shape and two of another shape. Select one shape as the dominant trait and represent it with a capital letter. Use a lower case letter to represent the recessive trait.
2. Using the objects, make a model to represent two parents, each of whom is heterozygous for the trait.
3. Move the objects in various combinations to represent all of the possible combinations of alleles from the parents. Using letters to represent the genotypes, record all the possible combinations of alleles in the offspring.

Analyze Your Results

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1. How many different arrangements of alleles can occur in the offspring of these parents?
2. What percentage of the offspring will have the dominant characteristic?
3. What percentage of the offspring will have the recessive characteristic?

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