Chromosomes contain the genetic material found in all cells. Each human cell has 23 pairs of chromosomes, including one pair of sex chromosomes and 22 pairs of non-sex chromosomes called autosomes. The sex chromosomes include the X chromosome and the Y chromosome. Females have two X chromosomes, while males have one X chromosome and one Y chromosome.
Genes are found within the chromosomes of all organisms. An individual's genes are present in a large molecule called deoxyribonucleic acid (DNA). DNA is made up of different combinations of four nucleic acids (adenine, thymine, cytosine, guanine), which are arranged in different lengths. The sequence of these molecules provides the "code," or instructions, for construction of each of the proteins involved in the development, growth, and function of all the cells in the body. An autosomal dominant disorder may occur when the nucleic acid sequences that make up individual genes are incorrect, or mutated. When a gene is mutated, the protein that it codes for may stop functioning or may no longer function properly, which can cause a disorder or disease.
Autosomes are the non-sex chromosomes. Individuals have two copies or alleles of the 22 autosomes (one copy inherited from each parent). Each parent can only pass one allele, or version of their genes, to their child. Which copy is passed down is determined by chance.
Autosomal dominant disorders are caused by a mutation in an autosomal gene. In order to have an autosomal dominant disorder, only one copy of the gene (inherited from either parent) needs to contain a disease-causing mutation. This is different from autosomal recessive disorders, in which a person needs to inherit two copies of a mutant gene to be affected by the disorder. Because males and females share the same autosomal chromosomes, they are affected equally by autosomal dominant disorders.
Huntington's disease, Marfan syndrome, familial adenomatous polyposis, and neurofibromatosis-1 are examples of autosomal dominant disorders. Huntington's disease is a neurological disorder characterized by abnormal body movements and a lack of coordination. Marfan syndrome is a connective tissue disorder characterized by abnormally long arms, legs, and fingers and a predisposition to cardiovascular problems. Familiar adenomatous polyposis is characterized by cancer of the large intestine and rectum. Neurofibromatosis-1 is characterized by tumors of the nervous tissue.
Allele, autosome, chromosome, dominant inheritance, familial adenomatous polyposis, gene therapy, genetic counseling, genetic testing, HTT gene, huntingtin gene, Huntington's disease, Marfan syndrome, neurofibromatosis-1, penetrance, prenatal testing.
types of the disease
Penetrance: Penetrance is a genetic term used to describe the proportion of individuals carrying a particular variation of a gene (an allele) that also express a particular trait (called the phenotype). For example, mutations in the huntingtin (HTT) gene responsible for Huntington's disease have 95% penetrance, meaning 95% of those with the allele for Huntington's disease develop the disease while 5% do not. Therefore, although Huntington's disease is inherited in an autosomal dominant manner, not every person who inherits the mutated gene will show symptoms of the disease. The degree of penetrance varies between diseases and cannot be predicted by genetic testing.