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Question Video: Applying Knowledge of Dominant and Recessive to Determine the Traits of an Offspring Science

Assume the gene for brown eyes is dominant over the gene for blue eyes. If a mother with blue eyes and a father with brown eyes have a child, what eye color is the child most likely to have?

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Video Transcript

Assume the gene for brown eyes is dominant over the gene for blue eyes. If a mother with blue eyes and a father with brown eyes have a child, what eye color is the child most likely to have?

This question asks about inheritance of eye color. In order to work out the correct answer, let’s discuss inheritance in terms of dominant and recessive alleles.

Recall that a trait refers to a specific characteristic, for example, eye color, hair color, or height, which is inherited from an organism’s parents. It is encoded by genes. And most body cells contain two genes coding for a trait, one from each parent.

In this question, we are asked about eye color as a trait. And the two different alleles of the gene coding for eye color are brown and blue. Note that brown eyes are represented by the color orange in our diagram. The question states that the allele coding for brown eyes is dominant over the allele coding for blue eyes. This means that the allele for brown eyes will be expressed if it is inherited from either parent, while to inherit blue eyes, the person must have two alleles coding for blue eyes. This means they must inherit the allele for blue eyes from both parents.

Let’s annotate the alleles coding for brown eyes with a capital B and the allele coding for blue eyes with a lowercase b. The father, who has brown eyes, will have one of two possible genotypes: capital B capital B or capital B lowercase b. Because the mother has blue eyes and the allele which codes for blue eyes is recessive, the mother must have the genotype lowercase b lowercase b. We can now use this information to create two Punnett squares and work out which eye colors are possible in a child of these two parents.

If the father has two dominant alleles, the child will have brown eyes because they will definitely inherit the dominant allele coding for brown eyes from the father. If the father has one dominant and one recessive allele, the child has a 50 percent chance of having brown eyes and a 50 percent chance of having blue eyes. We can observe that of the eight possible combinations of genes the child could inherit, only two will code for blue eyes.

Therefore, the answer to our question “What eye color is the child most likely to have?” is brown.

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