Dominant genetic disorders only require one faulty gene to be passed down from a parent, with a 50% chance of inheritance. Mutations in autosomes or X chromosomes can cause autosomal or X-linked dominant disorders, respectively. Men are more prone to X-linked disorders, while women can be carriers. Examples include Huntington’s disease and Rett syndrome. These disorders tend to be rare due to early mortality.
Dominant genetic disorders are diseases that require only one faulty copy of the gene to be passed down from parent to child. This means that only one parent with the defective gene is needed for the disease to be inherited. Disorders like these have a 50% chance of being passed on from parent to child. For a clearer example, two out of four children of an affected parent will most likely have the disorder.
The common cause of dominant genetic diseases is the mutation of a gene or a chromosome, the latter consisting of many genes. This mutation often occurs early in pregnancy, when the mother’s 13 chromosomes bind together with the father’s other 13 chromosomes, creating a cell that contains 26 chromosomes. During this stage where cells are copied, an error occurs resulting in a missing or extra chromosome, resulting in a genetic disorder.
Many of the dominant genetic disorders are caused by mutated autosomes, which are chromosomes that do not determine the sex of an offspring. Disorders like these are specifically called autosomal dominant disorders. An example would be Huntington’s disease, where the mutation appears on “chromosome 4”. Other examples include Marfan disease which causes a person to be abnormally tall and achondroplasia, the opposite of Marfan disease, which causes dwarfism.
Another specific type of dominant disorders are “X-linked dominant genetic disorders,” in which only the X chromosomes undergo a mutation. In these cases, men are more prone to pass on and inherit these disorders and experience worse symptoms than women. The reason for this is that women have two X chromosomes, where the defective copy is somehow “protected” by the non-defective copy of the X chromosome. Men, on the other hand, have both X and Y chromosomes, so the only chromosome X has no protection.
Passing on X-linked dominant disorders may depend on the affected parent. Typically, a male parent carrying the mutated X chromosome will not pass the disorder on to male offspring as the male passes on the Y chromosome to the next generation of males. The female offspring, on the other hand, will contain all the disease. With affected females, there will always be a 50% chance of passing the disorder to both male and female offspring. In some cases, an offspring will inherit and become a “carrier” of the disease, but will not necessarily show symptoms.
Examples of dominant X-linked disorders are Rett syndrome, which has shorter limbs and a smaller head, and incontinentia pigmenti, which involves discoloration of the skin and hair. Generally, all dominant genetic disorders tend to be rare, mainly because affected patients usually die in infancy and are, therefore, unable to father children. On occasions where affected patients give birth, the offspring will also most likely die young.
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