A
Adenine: One of the four bases that make up DNA. Abbreviated with an 'A'.
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B
Base: A small molecule inside the larger molecule of DNA. Bases - A, C, G, and T - are arranged in line in a DNA molecule (e.g. CGGTACAGG) and encode instructions for making proteins.
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C
Carrier: A person that carries a gene that causes a disorder, but does not show symptoms.
CGG repeat: A string of 3 bases that are usually repeated seven to 55 times in a row at the beginning of the FMR1 gene. The inactivation of this gene causes Fragile X. In people with Fragile X, the CGC triplet is repeated 200 times or more.
Chromosome: Chromosomes are packages of DNA found in the nucleus of cells. Humans have 46 chromosomes.
Cytosine: One of the four bases that make up DNA. Abbreviated with a 'C'.
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D
DNA: Short for deoxyribonucleic acid, DNA is the molecule that carries genetic information.
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F
Full mutation: A mutation in the FMR1 gene with 200 or more CGG repeats.
FMR1: A gene on the X chromosome that encodes instructions for building the Fragile X Mental Retardation Protein (FMRP). A mutation in this gene causes the Fragile X syndrome.
FMRP: A protein involved in the maturation of neurons in the brain. People with Fragile X lack this protein.
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G
Gene: A portion of DNA that contains instructions for making a protein.
Genotype: The genetic composition of a person. Usually used when considering one gene or chromosome (eg males have a XY genotype, females have a XX).
Guanine: One of the four bases that make up DNA. Abbreviated with a 'G'.
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M
Methyl group: A small molecule that turns off the FMR1 gene in people with Fragile X.
Mutation: A change in the sequence of a gene.
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P
PCR/Polymerase chain reaction: A method to increase or amplify specific sequences of DNA. This method can be used to detect the presence of changes in DNA sequence that can be the cause of genetic disorders.
PCR test: A genetic test used to detect pre-mutations in a person's DNA.
Pre-mutation: A version of the FMR1 gene with 55 to 199 CGG repeats at the beginning of the gene. A pre-mutation does not cause Fragile X but it can expand into a full-sized mutation in the egg or during a child's embryonic development.
Punnett square: A method of showing the potential offspring of two parents.
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S
Sex chromosome: Chromosomes (X and Y) that determine an individual's gender.
Sex-linked: Refers to genes found on the X chromosome. The inheritance and expression of the gene is thus linked to gender.
Southern blot test: A genetic test that detects full mutations in a person's DNA.
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T
Thymine: One of the four bases that make up DNA. Abbreviated with a 'T'.
Transmitting male: With reference to Fragile X, a transmitting male has a pre-mutation that he has passed to his daughter.
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X
X-inactivation: A process in female mammals in which one of the two X chromosomes is "turned off."
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