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Tag: Genetic Definitions I

Proactive Medical Genetic Testing with 23 and Me, Invitae and X Code for Life: Part 1 Deciding to Test.

February 20, 2019 Sarah

What is Genetic Testing? Genetic testing analyzes your genes, which are the instructions in your DNA. Your genes help determine your physical traits. It looks

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Genetic Definitions I

The glossary of terms is taken from a variety of sources: Centre for Genetic Health,

ADENINE (A):
One of the four basic building blocks (nucleotide bases) that makes up the genetic code or DNA. It is represented by the letter A.

ALLELE:
There are usually two copies of a gene. These two copies are called alleles. In some cases, one or both alleles will be mutated or altered in some way.

AUTOSOMAL DOMINANT MUTATION:
A dominant mutation in a gene which is carried on an autosome.

AUTOSOMAL GENE:
Any gene which is located on an autosome.

AUTOSOMAL RECESSIVE MUTATION:
A recessive mutation in a gene which is carried on an autosome.

AUTOSOME:
Any chromosome that is not a sex chromosome (that is not an X or Y chromosome). In humans, the autosomes are the numbered chromosomes and are given the numbers 1-22. Chromosome 1 is the largest and 22 is the smallest.

BASE PAIR:
Two complementary basic building blocks (nucleotide bases) that make up the genetic code, combine to form one rung of the DNA ladder.

BASES:
Also known as nucleotides, they are the basic components of DNA. They are denoted by the letters A (Adenine), G (Guanine), C (Cytosine) and T(Thymine). The sequence of these bases forms the genetic code.

CARRIER OF A MUTATED GENE:
Every cell contains two copies of each gene. One gene copy may be mutatedand the other may be ‘correct’. If the mutated gene is not expressed in the cells (resulting in a particular characteristic or a condition), the mutated gene is said to be recessive to the other ‘correct’ copy of the gene. An individual who has one correct gene copy and one faulty (recessive) gene copy is said to be a ‘carrier’ for the mutation leading to a specific condition. The carriers of a recessive mutation in a gene are usually not affected but they are at risk for passing on the faulty gene to their offspring.

CARRIER SCREENING:
Testing populations to determine if individuals are carriers of a mutated or faulty gene for a particular condition.

CARRIER TESTING
Testing an individual who is at risk due to a family history to determine if he or she is a carrier of a mutated or faulty gene for a particular condition.

CELL:
The basic structural unit of all living organisms. While some organisms are made up of only one or several cells, humans are composed of millions of cells. Each cell is enclosed by a membrane and has a nucleus which contains the genetic material (DNA) in the form of chromosomes. Mitochondria are also found randomly scattered throughout the cell.

CENTROMERE:
The constricted part of the chromosomes which separates it into its two arms. The short arm is called the ‘p’ arm (for ‘petite’); the long arm is called the ‘q’ arm (because q follows p in the alphabet).

CHROMOSOME:
A threadlike structure found in the nucleus of all the body cells (except red blood cells) consisting of DNA and proteins. Each chromosome can be thought of as a string of beads where every bead represents a gene.

CLINICAL GENETICS:
A specialty of medicine concerned with the diagnosis and provision for risks of developing an illness with a genetic basis in individuals and families.

CODON:

Three-letter words composed of combinations of the chemical letters A, G, C and T. These words make up the genetic code (DNA) that tells the cell to make a product (protein) that the cells can use. Also known as nucleotide triplets.

COMPLEX INHERITANCE:
Patterns of inheritance that differ from the ‘traditional’ (Mendelian) patterns of inheritance in that they require multiple factors (either genetic or environmental) for the condition to develop.

CROSSING OVER:
When chromosome pairs join together during meiosis (the division process which produces the egg and sperm cells), the two chromosomes may exchange material: part of one chromosome ‘crosses over’ and exchanges places with the corresponding part on its partner chromosome.

CYTOSINE (C):
One of the four basic building blocks (nucleotide bases) that makes up the genetic code (DNA). It is represented by the letter C.

 

Types of Genetic Testing

Genetic testing is “the analysis of chromosomes (DNA), proteins, and certain metabolites in order to detect heritable disease-related genotypes, mutations, phenotypes, or karyotypes for clinical purposes.” It can provide information about a person‘s genes and chromosomes throughout life.  I have not listed all the types of genetic testing. Information from Wikapedia

Carrier Testing

Carrier testing is used to identify people who carry one copy of a gene mutation that, when present in two copies, causes a genetic disorder. This type of testing is offered to individuals who have a family history of a genetic disorder and to people in ethnic groups with an increased risk of specific genetic conditions. If both parents are tested, the test can provide information about a couple’s risk of having a child with a genetic condition.

Diagnostic Testing

Diagnostic testing is used to diagnose or rule out a specific genetic or chromosomal condition. In many cases, genetic testing is used to confirm a diagnosis when a particular condition is suspected based on physical mutations and symptoms.

Diagnostic testing can be performed at any time during a person’s life, but is not available for all genes or all genetic conditions. The results of a diagnostic test can influence a person’s choices about health care and the management of the disease.  Diagnostic testing is used to diagnose or rule out a specific genetic or chromosomal condition. In many cases, genetic testing is used to confirm a diagnosis when a particular condition is suspected based on physical mutations and symptoms.

Forensic testing

    • Forensic testing uses DNA sequences to identify an individual for legal purposes. Unlike the tests described above, forensic testing is not used to detect gene mutations associated with disease. This type of testing can identify crime or catastrophe victims, rule out or implicate a crime suspect, or establish biological relationships between people (for example, paternity).

 

 

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