X-Linked Recessive
When a gene on the X chromosomes is affected, but it is unable to evoke the characteristic if heterozygous, it is said to be X-linked recessive. However, the characteristic is expressed in males because of their single X chromosome. Examples of X-linked recessive conditions include androgen insensitivity syndromes (both complete and incomplete), color blindness (red–green), G-6-PD deficiency, gonadal dysgenesis, hemophilia A and B, Lesch-Nyhan syndrome, and mucopolysaccharidosis II. The rules of X-linked recessive inheritance include the following. ● The characteristic occurs primarily in males. ● If both parents are unaffected but produce a
male with the characteristic, the mother is a carrier. ● If the father is affected and there is an affected male offspring, the mother must be at least heterozygous for the characteristic. ● A female with the abnormal characteristic may acquire it by the following: Inheritance of the recessive gene from both her mother and father (father affected, mother heterozygous), Inheritance of the recessive gene from one of her parents and expression occurs as a result of the Lyon hypothesis (functional selection of one X chromosome for this and subsequent progeny
male with the characteristic, the mother is a carrier. ● If the father is affected and there is an affected male offspring, the mother must be at least heterozygous for the characteristic. ● A female with the abnormal characteristic may acquire it by the following: Inheritance of the recessive gene from both her mother and father (father affected, mother heterozygous), Inheritance of the recessive gene from one of her parents and expression occurs as a result of the Lyon hypothesis (functional selection of one X chromosome for this and subsequent progeny
No comments: