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X and Y are sex chromosomes. Dominant inheritance occurs when an abnormal gene from one parent causes disease, even though the matching gene from the other parent is normal. The abnormal gene dominates. But in recessive inheritance, both matching genes must be abnormal to cause disease. If only one gene in the pair is abnormal, the disease does not occur or it is mild.
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Sex-linked Diseases: the Case of Duchenne Muscular Dystrophy (DMD)
Inheritance of Single-Gene Disorders - Fundamentals - MSD Manual Consumer Version
X-linked recessive inheritance is a mode of inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males who are necessarily hemizygous for the gene mutation because they have one X and one Y chromosome and in females who are homozygous for the gene mutation, see zygosity. X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes, while males have one X and one Y chromosome. Carrier females who have only one copy of the mutation do not usually express the phenotype , although differences in X chromosome inactivation can lead to varying degrees of clinical expression in carrier females since some cells will express one X allele and some will express the other. The current estimate of sequenced X-linked genes is and the total including vaguely defined traits is Some scholars have suggested discontinuing the terms dominant and recessive when referring to X-linked inheritance due to the multiple mechanisms that can result in the expression of X-linked traits in females, which include cell autonomous expression, skewed X-inactivation, clonal expansion, and somatic mosaicism.
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Inheritance of Single-Gene Disorders
Genes are segments of deoxyribonucleic acid DNA that contain the code for a specific protein that functions in one or more types of cells in the body. Chromosomes are made of a very long strand of DNA and contain many genes hundreds to thousands. Except for certain cells for example, sperm and egg cells , every human cell contains 23 pairs of chromosomes.
This page has been archived and is no longer updated. Knowledge about recessive X-linked gene-disease associations has led to the development and widespread use of prenatal diagnostic tests that can provide parents with information about whether their embryo or fetus might be carrying a disease mutation. Based on that information, the parents can either terminate the pregnancy or prepare for their future child, depending on their beliefs. You might expect that this kind of widespread testing has had the ultimate effect of decreasing the frequency of disease alleles in the population. In fact, the opposite is true, according to research by geneticist Ian Hastings of the Liverpool School of Tropical Medicine in England.