G

Gamete: The male sperm or female egg which fuse together to form a zygote.

Gamete Intra Fallopian Transfer (GIFT): A procedure in which eggs are retrieved from a woman, mixed with sperm and immediately replaced in one or other of the woman's fallopian tubes so that they fertilise inside the body (in vivo). 

Gene: The unit of inheritance. Everyone inherits two copies of each gene. A dominantly inherited genetic disease occurs when only one copy of the gene is sufficient to produce the disease e.g. Huntington's chorea. A recessively inherited disease only occurs if both copies of the defective gene are present e.g. Tay-Sachs' disease, Sickle cell disease. 

Genome: The basic set of genes in the chromosomes in any cell, organism or species. 

Gestone: A drug taken by injection following fertility treatment to support hormone levels.

Gonadotrophin Releasing Hormone (GnRH): Hormone released by the hypothalamus which stimulates the pituitary to produce Luteinising Hormone (LH) and Follicle Stimulating Hormone (FSH). 

Gonadotrophins: Drugs used to stimulate the ovaries similar in composition.

Gradient methods (sperm sorting): A method of sorting sperm based on the different constitution of X and Y sperm. Used for sex selection.