Question Video: Recalling the Difference between Dominant and Recessive Traits Science

Which of the following correctly compares dominant and recessive traits? [A] Recessive traits are always harmful to an organism, and dominant traits are rarely harmful. [B] Recessive traits will always be visible in the appearance of an organism, whereas dominant traits will only be visible 50% of the time. [C] Dominant traits, if present in an organism, will mask the appearance of recessive traits.

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Video Transcript

Which of the following correctly compares dominant and recessive traits? (A) Recessive traits are always harmful to an organism, and dominant traits are rarely harmful. (B) Recessive traits will always be visible in the appearance of an organism, whereas dominant traits will only be visible 50 percent of the time. (C) Dominant traits, if present in an organism, will mask the appearance of recessive traits.

Mendel’s experiments with pea plants greatly improved our understanding of inheritance. One theory that he proposed is the law of dominance. This law explains that if a parent with two dominant alleles reproduces with a parent with two recessive alleles, they will produce offspring that only show the dominant trait. Peas can be yellow or green, and these two traits are controlled by two different versions of a gene called alleles. The uppercase A is the dominant allele, and the lowercase a is the recessive allele.

Notice that all the offspring in this example are yellow, which is the dominant trait indicated by uppercase A. Even though the offspring contain both the dominant and recessive allele, only the dominant trait is expressed. You need two copies of the recessive allele for that trait to be expressed, as shown here with the green color with the two recessive alleles.

We can summarize all of this here. Dominant traits are always expressed if they’re present, while recessive traits are only expressed if the dominant trait is absent. Now let’s take a look at our answer choices.

Answer choice (A) states that recessive traits are always harmful, while dominant traits are rarely harmful. This is incorrect because this isn’t necessarily true. For example, the brown eye trait is dominant, while the blue eye trait is recessive. Neither cause harm to us.

Answer choice (B) is also incorrect. Recessive traits will not always be visible in organisms. In fact, in any organism that has the dominant allele, the recessive trait will not be visible. The dominant trait will be visible 100 percent of the time if it is present.

As we have seen, the correct answer is therefore (C). Dominant traits, if present in an organism, will mask the appearance of recessive traits.

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