This is due to the fact that, typically, females have two copies of the X-chromosome, while males have only one copy. Genetics Īs the X chromosome is one of the sex chromosomes (the other being the Y chromosome), X-linked inheritance is determined by the sex of the parent carrying a specific gene and can often seem complex. Some X-linked dominant conditions are embryonic lethal in males, making them appear to only occur in females. When the son is affected, the mother will always be affected. However, if the mother is also affected then sons will have a chance of being affected, depending on whether a dominant or recessive X chromosome is passed on. All fathers that are affected by an X-linked dominant disorder will have affected daughters but not affected sons. The exact pattern of inheritance varies, depending on whether the father or the mother has the trait of interest. X-linked dominant traits do not necessarily affect males more than females (unlike X-linked recessive traits). In this case, someone who expresses an X-linked dominant allele will exhibit the disorder and be considered affected. In medicine, X-linked dominant inheritance indicates that a gene responsible for a genetic disorder is located on the X chromosome, and only one copy of the allele is sufficient to cause the disorder when inherited from a parent who has the disorder. As an inheritance pattern, it is less common than the X-linked recessive type. Because of the relative similarity of sequence mtDNA is also used in species identification in ecology studies.X-linked dominant inheritance, sometimes referred to as X-linked dominance, is a mode of genetic inheritance by which a dominant gene is carried on the X chromosome. Mitochondrial DNA polymorphisms are also used to investigate evolutionary lineages, both ancient and recent. These mutations can affect both males and females, but males cannot pass them on as the mitochondria are inherited via the egg, not the sperm. There are some human diseases associated with mutations in mitochondria genes. Mutations in Mitochondrial DNA are inherited through the maternal line (from your mother). For example, the Y-chromosome of Mongolian ruler Genghis Khan (1162-1227 CE), and his male relatives, accounts for ~8% of the Y-chromosome lineage of men in Asia (0.5% world wide). Y-chromosome DNA polymorphisms can be used to follow the male lineage in large families or through ancient ancestral lineages. As expected this trait is passed on from father to all sons and no daughters. An example of Y-linked inheritance is the hairy-ear-rim phenotype seen in some Indian families. This is the easiest mode of inheritance to identify, but it is one of the rarest because there are so few genes located on the Y-chromosome.
There is only father to son transmission. Only males are affected in human Y-linked inheritance (and other species with the X/Y sex determining system). Two additional modes are Y-linked and Mitochondrial inheritance. \): A pedigree consistent with AD inheritance.
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