Dominant vs. Recessive Alleles

Dominant vs. Recessive Alleles
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  • 0:15 Mendelian Inheritance
  • 0:50 Dominant Alleles
  • 1:17 Recessive Alleles
  • 1:52 Genetic Diseases and Disorders
  • 2:27 Lesson Summary
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Instructor: Yuanxin (Amy) Yang Alcocer

Amy has a master's degree in secondary education and has taught math at a public charter high school.

Watch this video lesson to learn about Mendelian inheritance. It explains why we have the eye color that we have as well as the reason that some people have certain disorders and others don't.

Mendelian Inheritance

Why do some people have brown eyes? And how come only a few people have really blue eyes? And what about those diseases that are said to be genetic or passed on from generation to generation? What accounts for this? According to Gregor Johann Mendel, each parent contributes an allele for each gene and the dominant allele is the one that determines what that particular gene will do. This is called Mendelian inheritance. It describes the genes that determine what color eyes you have and everything else that is genetic. Each gene is made up of two alleles, one from each parent. An allele is simply one part of a gene.

While Mendelian inheritance does explain a lot of how we get our characteristics, it does not explain all situations. It's important to remember that some situations have other mechanisms at play that are not discussed in this lesson.

Dominant Alleles

An allele is said to be dominant when it overpowers other alleles. For example, the allele for brown eyes is dominant because if you have this allele then you will have brown eyes. It won't matter what the other allele is. Say your mom has brown eyes. If she gives you an allele for brown eyes, then you will have brown eyes no matter what. Even if your dad has green or blue eyes, you will have brown eyes if your mom gives you the brown eyes allele.

Recessive Alleles

An allele is said to be recessive when both alleles are needed for the effect to show. The allele for blue eyes is recessive because BOTH your parents need to give you the blue eyes allele for you to have blue eyes. This is why there are so many more people with brown eyes than there are people with blue eyes. This is not to say that there are fewer people that carry the blue eyes allele. It is very possible for some brown-eyed people to carry one blue eyes allele, but because the other allele is the dominant one for brown eyes, they will have brown eyes. Only those people with two blue eyes alleles will have blue eyes.

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