Genetics Review

Alleles are passed from parent to offspring and are either dominant or recessive. Dominant alleles are always expressed with a capital letter, for example D. Recessive alleles are always expressed with a lower case letter, for example d.

• If an individual has two dominant alleles they are said to be homozygous dominant.
• If an individual has two recessive alleles they are said to be homozygous recessive.
• If an individual has inherited both a dominant and recessive allele they are said to be heterozygous.
• Heterozygous individuals typically take on the dominant trait except in the presence of codominance. This means you will end up with a combination of both traits.

Remember we are talking about genotypes, or the actual genetic makeup of an individual and which alleles they inherited.  When we talk about the trait this is the phenotype or appearance of certain genetically determined traits. The alleles an individual inherits for a specific trait determines the phenotype.

Close This Window