Module 6 Lesson 3 - 8
Lesson 3 — Incomplete Dominance, Codominance, and Multiple Alleles
Lesson Summary
During this lesson, you were to focus on two essential questions:
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What happens when one allele is not completely dominant over another?
- How does having more than two alleles for a gene affect the possible phenotypes for a trait?
By adding knowledge of multiple alleles and incomplete dominance to your earlier knowledge of genetics, you have expanded your ability to interpret phenotypes and predict inheritance. All this and you are still working with only one gene! Accept that each chromosome has hundreds of genes and humans have 23 chromosome pairs. Think of all the possible variations!
Understanding blood types and their inheritance pattern can go a long way when working with family histories, developing pedigrees (charts that trace the inheritance of genetic characteristics through generations), and determining paternity.
In Biology 20, you learned about the various types of blood and the consequences of a person receiving incompatible blood. In this lesson, you examined the three alleles for blood type and how they account for the four phenotypes possible. Using this information, you can predict possible blood types of future children, study family pedigrees to determine lineage, and even determine if there was a mix up in the hospital!
In cases where one allele is not completely dominant over another, each allele is somewhat expressed. If the heterozygous phenotype appears to be more of a blend, as with flower colour, this is called incomplete dominance. Codominance occurs when each allele is fully expressed in different parts, as with red and white hairs in roan horses.
