X-linked recessive

X-linked recessive is a mode of genetic inheritance by which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males (who are necessarily homozygous for the gene mutation because they have one X and one Y chromosome) and in females who are homozygous for the gene mutation (i.e., they have a copy of the gene mutation on each of their two X chromosomes).

Genetic Inheritance

Genetic inheritance is the process by which genetic information is passed on from parent to child. This is the mechanism that determines how many of our physical and physiological characteristics are defined. In the case of X-linked recessive inheritance, the gene carrying the mutation is located on the X chromosome.

X Chromosome

The X chromosome is one of the two sex-determining chromosomes in many animal species, including humans. The other is the Y chromosome. Humans and most other mammals have an XY sex-determination system, which means that the sex of an offspring is determined by the sex chromosomes it inherits from its parents.

Y Chromosome

The Y chromosome is one of the two sex chromosomes in mammals, including humans, and many other animals. The other is the X chromosome. Y is the sex-determining chromosome in many species, since it is the presence or absence of Y that determines the male or female sex of offspring produced in sexual reproduction.

Homozygous

Homozygous refers to having identical pairs of genes for any given pair of hereditary characteristics. In the context of X-linked recessive inheritance, a female would need to be homozygous for a particular gene mutation (i.e., have a copy of the gene mutation on each of her two X chromosomes) in order for the phenotype associated with that mutation to be expressed.

Phenotype

The phenotype is the set of observable characteristics of an individual resulting from the interaction of its genotype with the environment. In the context of X-linked recessive inheritance, the phenotype associated with a particular gene mutation is typically only expressed in males and in females who are homozygous for the gene mutation.

See Also

• Genetic inheritance
• X chromosome
• Y chromosome
• Homozygous
• Phenotype

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