Genetics 101

Genetics 101: The First Step to Understanding Genetic Risks

Genes are the basic physical and functional units of heredity.  Genes are made up of DNA and act as instructions for our body to grow and develop properly.  The Human Genome Project has estimated that humans have between 20,000-25,000 genes.  Genes are stored in packages called chromosomes.

Every person has two copies of each gene, getting one copy from each parent.  Genes tell the cells how to make proteins, which do the work (such as the collagen that provides strength to our skin and the enzymes that digest our food).  Most genes are the same in all people, but a small number of genes (less than 1%) are slightly different between people.  Small differences in these genes contribute not only to each person’s unique physical features, including skin and hair color, but also how well the organs in our body work.

Some genetic changes are very rare while others are common in the population.  The genetic changes, also called mutations, that cause thoracic aortic aneurysms and dissections to be inherited, or run in families, are very rare.  It is important to note that genes themselves do not cause disease — genetic disorders are caused by mutations that make a gene, and subsequently the protein, function improperly.

A gene mutation is a permanent change, or alteration, in the DNA that makes up a gene.  Mutations can be inherited from a parent or show up for the first time in an individual.  Mutations that are passed from parent to child are called hereditary mutations.  This type of mutation is present throughout a person’s life in virtually every cell of the body.  Sometimes, genetic mutations prevent one or more genes from working properly.  By changing a gene’s instructions, a mutation can cause a normally-occurring protein to malfunction or be missing entirely.  When a mutation alters a protein that plays a critical role in the body, it can disrupt normal development or cause a medical condition.  A condition caused by mutations in a gene is called a genetic disorder.

For more information about DNA, genes, and how they work, visit Genetics Home Reference.




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