Indicate the type of inheritance involved in each of the following situations.
(c) The trait is expressed more commonly in sons than in daughters.

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Understand the concept of inheritance patterns: Traits can be inherited through autosomal or sex-linked inheritance. Sex-linked inheritance involves genes located on sex chromosomes (X or Y).

Recognize that traits expressed more commonly in sons than in daughters often suggest X-linked inheritance. This is because males have only one X chromosome, so a recessive allele on the X chromosome will be expressed in males.

Recall that females have two X chromosomes, so they would need two copies of the recessive allele for the trait to be expressed. This makes the trait less common in daughters.

Consider examples of X-linked traits, such as hemophilia or color blindness, which are more frequently observed in males due to the inheritance pattern.

Conclude that the type of inheritance involved in this situation is likely X-linked recessive inheritance, based on the description of the trait being more common in sons than daughters.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Sex-Linked Inheritance

Sex-linked inheritance refers to traits that are associated with genes located on sex chromosomes, particularly the X and Y chromosomes. In many cases, traits linked to the X chromosome are expressed differently in males and females due to the presence of only one X chromosome in males (XY) compared to two in females (XX). This can lead to certain traits being more commonly expressed in males, especially if the trait is recessive.

Autosomal vs. Sex-Linked Traits

Autosomal traits are those determined by genes located on non-sex chromosomes (autosomes), while sex-linked traits are influenced by genes on sex chromosomes. Understanding the distinction is crucial for determining inheritance patterns. If a trait is expressed more in sons than daughters, it often indicates a sex-linked inheritance pattern, particularly if the trait is recessive and located on the X chromosome.

Recessive and Dominant Alleles

Alleles can be classified as dominant or recessive based on their expression in the phenotype. A dominant allele will mask the effect of a recessive allele in a heterozygous individual. In the context of sex-linked traits, if a recessive allele is present on the X chromosome, it may be expressed in males who have only one X chromosome, leading to a higher prevalence of the trait in sons compared to daughters.

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Dominant vs. Recessive Alleles

Related Practice

Textbook Question

Indicate the type of inheritance involved in each of the following situations.

(a) Children who exhibit the trait have at least one parent who also exhibits it.

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Textbook Question

Hemophilia A, a condition in which blood does not clot properly, is a recessive trait located on the X chromosome (Xʰ). Suppose that a woman who is heterozygous for this trait (XXʰ) has children with a normal male (XY). What is the probability that the couple will have daughters with hemophilia? What is the probability that the couple will have sons with hemophilia?

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Textbook Question

Indicate the type of inheritance involved in each of the following situations.

(b) Children exhibit the trait even though neither parent does.

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Textbook Question

Distinguish between the following paired terms:

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Textbook Question

Indicate the type of inheritance involved in each of the following situations.

(d) The trait is expressed equally in daughters and sons.

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