Introduction to Genetics: Glossary A-M

Page content

For anyone wanting to study genetics or who is just curious about the subject, this is an ideal introduction to genetics, to keep you up-to-speed with some of the key terms.


One of two variants of a gene at a particular locus. There are two versions of each gene, and they are known as alleles. You inherit one allele from your father and one allele from your mother of each gene. A dominant allele can be expressed over a recessive allele.

Amino Acids

These are the building blocks of proteins; they link together to form long chains. There are 20 different types of amino acids.


Any chromosome that is not a sex chromosome. Humans have 22 pairs of autosomes.

Base Pair

Two bases that form a “rung” in the DNA “ladder”. In DNA there are four bases, adenine (A), guanine (G), cytosine (C) and thymine (T). A will always bind to T, and G will always bind to C.

Candidate Gene

A gene that is suspected of being involved in a genetic disease. It is likely that the protein coded for by the gene is absent or abnormal in some way.


A triplet of bases (three bases) in a DNA or RNA sequence which specify one amino acid.

Fluorescence in situ hybridization (FISH)

A process used to detect chromosomal abnormalities. Chromosomes or parts of chromosomes are stained/painted with fluorescent molecules.

Genetic Counseling

Genetic counseling is where individuals and families with a history of a genetic disease, or who are at risk of contracting the disease are given information by trained professionals. It helps them to make informed decisions.


The number of chromosomes in a sperm or egg cell. It’s half the diploid number.

Homologous Recombination

Also known as crossing over. This is where genes and DNA segments are shuffled about and exchanged between two similar DNA strands during the formation of eggs and sperm. It creates genetic diversity.


The full chromosomal complement of an individual.

Mitochondrial DNA

Mitochondrial DNA is distinct from nuclear DNA. It’s found inside the mitochondria, the energy factories of the cell.

Go to Part Two: N-Z