Question

How is an X-linked trait different from an autosomal trait? (page \(481)\)

Short answer

X-linked traits are determined by genes located on the X chromosome, with males being hemizygous and females being either homozygous or heterozygous. X-linked recessive traits are more likely to be expressed in males than in females. Autosomal traits, however, are determined by genes on non-sex chromosomes and have the same inheritance pattern in both males and females. The expressivity of autosomal traits is also equal in both sexes. The difference between X-linked and autosomal traits lies in their location on chromosomes, inheritance patterns, and expressivity in males and females.

Step-by-step solution

Definition of X-linked traits

X-linked traits are those that are determined by genes located on the X chromosome. Since females have two X chromosomes (XX), they can be either homozygous (having two copies of the same allele) or heterozygous (having one copy of each allele) for a given X-linked trait. Males, on the other hand, have only one X chromosome (XY), which means they have just one copy of any given gene on the X chromosome. Thus, males are hemizygous for X-linked traits and express the trait regardless of whether the allele is dominant or recessive.

Definition of Autosomal traits

Autosomal traits are determined by genes located on the non-sex chromosomes, also known as autosomes. There are 22 pairs of autosomes in humans. For these traits, the inheritance pattern is the same in both males and females, as both have two copies of each autosome (one from each parent). An individual can be homozygous dominant, heterozygous, or homozygous recessive for a given autosomal trait.

Inheritance Patterns

The inheritance pattern for X-linked traits is different from that of autosomal traits. For X-linked traits, the inheritance pattern is determined by the sex of the parent carrying the gene and the sex of the offspring. Female carriers can pass on the X-linked gene to both their sons and daughters. In contrast, males can only pass on the X-linked gene to their daughters. For autosomal traits, the inheritance pattern is not influenced by the sex of the parent or the offspring. Both parents contribute one allele each, and the offspring's phenotype is determined by the combination of these alleles (dominant or recessive).

Expressivity in Males and Females

X-linked recessive traits are more likely to be expressed in males than in females. This is because males have only one X chromosome, and if it carries the recessive allele, they will express the trait. Females, on the other hand, need two copies of the recessive allele to express the trait. Since females have two X chromosomes, they are less likely to express X-linked recessive traits. Autosomal traits, however, are equally likely to be expressed in both males and females, as the inheritance pattern is the same for both sexes. In summary, X-linked traits are different from autosomal traits because of their location on the X chromosome, resulting in distinct inheritance patterns and differences in the way these traits are expressed in males and females.