Question

Genes located on a sex chromosome are said to be a. X-linked. b. dominant. c. hemizygous. d. sex-linked. e. autosomal.

Short answer

The correct answer is d. sex-linked.

Step-by-step solution

Understanding Terminology.

First, let's understand the terminology. X-linked genes are those that are located on the X chromosome. When a gene is dominant, it means its effect is visible in the organism. Hemizygous refers to the genes present on the single X-chromosome in males (XY). Sex-linked genes are located on either of the sex chromosomes, X or Y. Autosomal genes are those located on the non-sex chromosomes, chromosomes 1 to 22 in humans.

Matching the definition

Now let's match the definitions to the question, which is looking for a term that signifies genes located on a sex chromosome. The most broad term is 'sex-linked' as it can refer to genes on either of the sex chromosomes, X or Y.

Key concepts

X-linked genes

X-linked genes are those genes that are found on the X chromosome. Chromosomes are thread-like structures that carry genetic information, and humans typically have 23 pairs of them. The X chromosome is one of the two sex chromosomes in humans, the other being the Y chromosome. The presence of X-linked genes is important because they often have different patterns of inheritance compared to genes on non-sex chromosomes.
- In females (XX), these genes may exist in two copies, while in males (XY), there is only one copy. - This means that recessive traits linked to X-linked genes can be expressed in males even if they only have one recessive allele, making certain genetic disorders more common in males.

Autosomal genes

Autosomal genes are located on non-sex chromosomes, also known as autosomes. Humans have 22 pairs of autosomes, numbered 1 through 22, which are the same in both males and females.
- These genes are inherited in a typical Mendelian fashion. - Both males and females have two copies of each autosomal gene, one inherited from each parent. - Disorders caused by mutations in autosomal genes are referred to as autosomal disorders and can be dominant or recessive, affecting males and females equally.

Dominant genes

Dominant genes are those whose traits are expressed the moment even one copy is present. Dominance refers to how certain traits are visible in an organism. If you have a pair of alleles (one from each parent) and one of them is dominant, that trait will be shown regardless of the other allele.
- Dominant genes can be on any chromosome: autosomal or sex chromosome. - They can mask the presence of a recessive gene. - An example is the gene for brown eyes, which is typically dominant over the gene for blue eyes.

Hemizygous

The term hemizygous describes a state where only one copy of a gene is present in a diploid organism. In humans, this is a common scenario for males concerning genes on the X chromosome.
- Males (XY) have one X and one Y chromosome, making them hemizygous for the genes on these chromosomes. - In contrast, females (XX) have two copies of each X-linked gene, which allows for heterozygous or homozygous expression. - Hemizygous conditions can lead to a different pattern of inheritance for X-linked disorders, where males may express recessive traits if present on the X chromosome.