The human genome is passed on from generation to generation, from parents to offspring. Human inheritance is governed by Mendelian inheritance and non-Mendelian inheritance patterns. Although many beneficial and necessary genes are passed on, so are mutated genes that cause genetic disorders, such sickle-cell anemia. One goal of biotechnology is to use genetic material itself to treat these disorders, such as in gene therapy.
Gene: Segment of DNA that codes for a single protein or RNA. Controls what characteristics are expressed.
Trait: A variation of a characteristic. For example, hair is a characteristic and brown hair is a trait.
Allele: Variant of a specific gene. Codes for different traits.
X-Linked Trait: Coded for by a gene on an X sex chromosome.
Pedigree: Charts familial relationships and the inheritance of a specific trait.
Genetic Disorder: A genetic disorder may be caused by a mutation at the gene level or by an unusual number of chromosomes.
Single-Gene Disorder: Disorder caused by the mutation of a single gene.
Chromosomal Disorder: Disorder caused by an unusual number of chromosomes.
Nondisjunction: Failure of replicated chromosomes to separate.
The Mendelian pattern of inheritance assumes that traits are
controlled by only one gene and that each gene has only two alleles.
Examples of traits that exhibit the Mendelian pattern of inheritance:
Diseases caused by Mendelian traits,ortraits that exhibit the Mendelian pattern of inheritance, include sickle-cell anemia and cystic fibrosis.
Pedigrees are useful for examining how traits are passed from generation to generation. The example below shows how an autosomal recessive trait is passed through a family.
Non-Mendelian inheritance is a more complex pattern of inheritance, involving multiple genes, multiple alleles, and multiple traits.
Genetic disorders can be the result of mutations at the gene level or by unusual number of chromosomes.
Below are some various classifications of single gene disorders:
Chromosomal disorders are caused by problems at the chromosome level.
One way parents who have recessive genetic disorders check for the presence of the disorder in their fetus is by prenatal testing.
One possible way to treat genetic disorders is by gene therapy. Gene therapy uses a vector, usually a virus, to insert or express a functional gene in target cells. The gene will counter the harmful effects of the mutated gene(s).