The Influence of Single Gene-Pair Inheritance on Development

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  • 0:07 What Is Genetic Inheritance?
  • 0:32 Single Gene-Pair Inheritance
  • 3:06 Predictable Patterns
  • 4:44 Lesson Summary
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Lesson Transcript
Instructor: Lisa Roundy

Lisa has taught at all levels from kindergarten to college and has a master's degree in human relations.

What is single gene-pair inheritance? What influence does it have on human development? Learn the answers to these questions as we explore this area of genetic inheritance in this video lesson.

What Is Genetic Inheritance?

Let's meet Stacey and her parents.

Stacey inherited traits from her parents.
image of girl

Most of us will understand when we look at Stacey that she has her mother's blue eyes and her father's red hair. All of her characteristics are inherited from her parents in some way. How does this process take place? Genetic inheritance is the process by which genes are passed down from a parent to their offspring. One way that this can occur is through single gene-pair inheritance.

Single Gene-Pair Inheritance

Single gene-pair inheritance occurs when a trait is linked to one gene-pair that consists of two alleles. This is also referred to as Mendelian inheritance. An allele is one part of the gene-pair. One allele is inherited from the father, and one is inherited from the mother.

Let's look at a chart that shows some examples of possible gene-pairs before we go further.

possible gene-pairs

Each gene-pair is made up of two parts. We will use the letter 'A' to represent the two parts of the gene-pair. There are three possible combinations that can exist: two capital A's (AA), a capital 'A' and a lowercase 'a' (Aa), and two lowercase 'a's (aa). What is the difference between a lowercase 'a' and a capital 'A' you may ask? The answer is that it represents whether the trait is dominant or recessive. A capital 'A' stands for an allele with a dominant trait. A lowercase 'a' stands for an allele with a recessive trait.

Let's look at a recessive trait first. We are assuming that the gene-pair we are discussing determines if a person will be an albino, or a person that has no pigment in their skin, eyes, or hair. Let's say that capital 'A,' or the dominant trait, is the allele for the trait of normal pigment, and let's say that lowercase 'a' is the allele for the recessive trait of being an albino. If a person has two dominant alleles in their gene-pair, they will have normal pigment. If a person has a dominant allele and a recessive allele for their gene-pair, they will have normal pigment but will be a carrier for the albino trait and could have a child who is an albino. If a person has two recessive alleles for their gene-pair, they will be an albino.

recessive inheritance

Now let's use eye color to examine a dominant trait. Let's say that capital 'A,' the dominant trait, is the trait for brown eyes, and the lowercase 'a,' the recessive trait, is the trait for blue eyes. If a person has two dominant alleles in their gene-pair, they will have brown eyes. If a person has one dominant allele and one recessive allele for their gene-pair, they will have brown eyes because it's the dominant trait, but they could have a child who is born with blue eyes because they carry the trait for blue eyes as well. If a person has two recessive alleles for their gene-pair, they will have blue eyes.

dominant inheritance

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