Inheritance is how we receive genes from our parents, which decide our traits or characteristics.
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Video Transcription
Inheritance is how we receive genes from our parents, which decide our traits or characteristics. Traits are things like the color of our eyes, our hair, or how our body works. These traits are coded in our DNA, which acts like a set of instructions in every cell of our body.
But where do these instructions come from? They’re organized into structures called chromosomes, which are found in the nucleus of our cells. Humans have 46 chromosomes in total, arranged into 23 pairs. One chromosome in each pair comes from our mother, and the other comes from our father. These chromosomes carry the genes that determine our traits.
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How Traits Are Passed Down
Each trait can come in different versions. For example, the gene for eye color can have several versions, such as:
- Blue eyes
- Brown eyes
- Green eyes
- Gray eyes
Some versions of a gene are stronger, and we call these dominant. Others are weaker, and we call these recessive. In inheritance, we get one gene for each trait from each parent, so we end up with two genes for every trait.
If one gene is dominant and the other is recessive, the dominant gene will “win,” and that trait will show up. For example, brown eyes are dominant, and blue eyes are recessive. So, if you get one gene for brown eyes from one parent and one gene for blue eyes from the other parent, you will have brown eyes because the brown eye gene is dominant.
However, if both parents give you the recessive gene for blue eyes, then you will have blue eyes, because there is no dominant gene to “take over.”
This same process happens with other traits, like hair color, height, or whether you can roll your tongue.
Homozygous and Heterozygous Traits
Each trait is made up of two parts, or genes. If these two genes are the same, we call it homozygous (homo means “the same” in Latin).
If the two genes are slightly different, we call it heterozygous (hetero means “different” in Latin).
For example, if we say that John is homozygous for brown eyes, it means both of the genes for eye color are the same—two brown eye genes.
Marie, on the other hand, is heterozygous for brown eyes. This means she has one dominant gene (brown) and one recessive gene (blue). Her eyes are brown because the brown gene is stronger (dominant), but she still carries the blue gene, which her children could inherit.
Chromosomes and Sex Determination
Now, let’s talk about one special pair of chromosomes called the sex chromosomes, which determine biological sex. Of the 23 pairs of chromosomes, 22 pairs are the same for everyone, but the 23rd pair is different.
Females have two X chromosomes, written as XX, while males have one X and one Y chromosome, written as XY.
The X chromosome carries many more genes than the Y chromosome, and some of these genes control traits and even health conditions.
Some traits and conditions are linked to genes on the X chromosome. These are called “X-linked traits.” If the gene causing the condition is recessive, it’s called an “X-linked recessive mutation.”
On the GED test, you might see a question that mentions the term “X-linked recessive mutation,” which means the question is related to male or female chromosomes. We will learn more about this in the next lesson about Punnett squares. For now, let’s solve a few quizzes.
Last Updated on January 19, 2026.