Problem 5 - Biology: The Unity and Diversity of Life

Question

True or false? A son can inherit an X-linked recessive allele from his father.

Step-by-Step Solution

Answer

False, a son inherits his X chromosome from his mother, not his father.

Step 1: Understanding X-linked Recessive Inheritance

X-linked recessive alleles are located on the X chromosome. In such genetic inheritance, a male (XY) inherits his X chromosome from his mother and his Y chromosome from his father. Hence, females (XX) receive one X chromosome from each parent, while males receive the Y chromosome from the father.

Step 2: Considering the Father's Contribution

Since the son receives only the Y chromosome from his father, any allele located on the X chromosome that the father possesses cannot be passed directly to his son. The son’s X chromosome is exclusively inherited from his mother.

Step 3: Conclusion

Since a father does not contribute an X chromosome to his male offspring, a son cannot inherit an X-linked recessive allele from his father. Thus, the statement is false.

Key Concepts

Chromosomes

In human genetics, chromosomes are structures within our cells that contain DNA, which holds our genetic information. Humans typically have 23 pairs of chromosomes, totaling 46. These include 22 pairs of autosomes and one pair of sex chromosomes.
The sex chromosomes determine an individual's sex, with females having two X chromosomes (XX) and males having one X and one Y chromosome (XY). Each parent contributes one chromosome to each pair, so offspring inherit half of their chromosomes from each parent.
Chromosomes play a crucial role in genetic inheritance as they carry alleles, the variants of genes. Therefore, understanding how chromosomes are passed from parents to children forms the foundation of understanding genetic traits and inheritance patterns.

Genetic Inheritance

Genetic inheritance is the process by which genes and traits are passed from parents to offspring. This is governed by the principles of Mendelian inheritance, where alleles are inherited from both mother and father.
In the case of X-linked recessive inheritance, the gene for a trait is located on the X chromosome. Recessive alleles require two copies (in females) or one copy (in males) for the trait to be expressed.
Males are more often affected by X-linked recessive conditions because they only have one X chromosome. If this chromosome carries a recessive allele, there is no corresponding allele on a Y chromosome to counter its expression. Conversely, females with one recessive allele are usually carriers, as they have another X chromosome that likely carries a dominant allele.

Alleles

Alleles are different forms of a gene that determine traits. For any given gene, there may be several possible alleles. A child inherits one allele from each parent for each gene, contributing to variations in physical appearance and health.
In X-linked inheritance, alleles on the X chromosome can be dominant or recessive. The focus is often on recessive alleles, especially in cases of genetic disorders like hemophilia or color blindness.
For males, having only one X chromosome means that whatever allele is present will determine the trait, as there is no second X chromosome to provide an alternative allele. This makes understanding alleles crucial for insights into genetic conditions and performing genetic analysis.