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A gamete is a reproductive cell that exists in both males and females and is haploid in its mature form. The egg (ovum) is the female gamete, and the sperm is the male gamete. Fertilization occurs when the male and female gametes unite to form a zygote.

Gamete intrafallopian tube transfer (GIFT) is an assisted reproductive technology. First, eggs are removed from the woman’s ovary, and a sperm sample is collected from the man. Then, the two are delivered via catheter to the woman’s fallopian tube, where fertilization will hopefully take place. This differs from IVF, in that the fertilization occurs in the woman’s body as opposed to inside a petri dish.

Gametogenesis is the combination of all the processes needed to make gametes (or sex cells, the egg and the sperm). Gametogenesis refers to spermatogenesis in the male and oogenesis in the female. During gametogenesis, diploid precursor cells go thorough meiosis to produce haploid cells, and these haploid cells go through processes of differentiation to form mature gametes capable of undergoing fertilization.

The gastrula is an early post-implantation embryo that develops from the blastula. It consists of three layers of cells: the ectoderm, mesoderm, and endoderm. The process of differentiation into three germ layers is called gastrulation.

In vertebrates, gastrulation is a major morphogenetic event that results in organization of the overall body plan and generation of the primary germ layers.

Gelation is the transition of a liquid to a solid-like gel. Gelation occurs when a solution of dilute polymers is cross-linked into a network.

Gender refers to the socially constructed concepts of women and men based on appearances, actions, thoughts, and behaviors. Gender does not necessarily refer to biological differences, such as genitalia present at birth or chromosomal differences, and it can vary depending on specific sociocultural expectations of women and men.

Proteins are the functional units in cells that are encoded within defined regions of DNA. These regions are called genes, and genes are inherited from parents. Humans contain ~20,000 protein-coding genes. Collectively, all the genes in an organism are referred to as a genome.

A technique that manipulates one of an organism's genes to understand its function, either by deletion (gene knockout: abbreviation KO) or insertion (gene knockin: abbreviation KI). Gene knockout/knockin is induced by a Cre-LoxP system that deletes or inserts genes of interest. Double knockout (abbreviation DKO) is the deletion of two genes simultaneously. 

A germ cell is a reproductive, haploid cell (in humans, a germ cell - either an egg or sperm cell - has 23 chromosomes).

In gametogenesis, a germ cell nest is a collection of immature primordial follicles connected by intercellular bridges due to incomplete cytokinesis thus far in the process. It is thought that this early connection is important in avoiding the production of defective germ cells.

The germinal vesicle is the nucleus of an oocyte that is arrested in prophase of meiosis I. The nuclear envelope of the germinal vesicle will break down in a process known as germinal vesicle break down (GVBD) when the oocyte resumes meiosis in response to the luteinizing hormone (LH) surge that occurs prior to ovulation.

Germinal vesicle breakdown (GVB) refers to the dissolution of the nucleus of an oocyte that is arrested in prophase of meiosis I (the breakdown of the germinal vesicle). In this stage, the oocyte resumes meiosis in response to the luteinizing hormone (LH) surge that occurs prior to ovulation. The oocyte will arrest in meiosis II at the metaphase (MII) stage, where it stays until fertilized by sperm.

The gestation period refers to the length of time between conception and birth (in humans, this is 266 days, which is just short of nine months). The gestation period varies among different species.

A gestational carrier, also referred to as a gestational surrogate, is a woman who agrees to carry and give birth to a child for another woman or couple who may be infertile. Gestational carriers use a fertilized embryo created using in vitro fertilization that is then surgically placed into their uterus. In order to prepare the uterus for conception and to carry the fetus to term, gestational carriers will need to take hormones. They are expected to surrender the infant to the genetic parents upon birth. The gestational carrier has no biological relationship to the embryo she is carrying. Gestational carriers differ from a traditional surrogate, as a surrogate, along with giving birth, provides the egg for fertilization. Several legal issues are related to gestational surrogacy and are typically addressed in advance of an arrangement. These legal issues vary from state to state.


The glans penis refers to the tip of the male penis, often known as the “head.” In uncircumcised males, the glans penis is covered by prepuce (foreskin) when the penis is not erect.

A gonad is a reproductive gland that produces ova (eggs) in females and sperm in males. Female gonads are ovaries, whereas male gonads are testes (testicles). Both organs also produce hormones.

Gonadotoxicity is the temporary or permanent damage to ovaries or testes after exposure to certain substances or drugs. Aggressive chemotherapy and radiotherapy used for the treatment of some cancers and autoimmune diseases are the most common causes of gonadotoxicity and subsequent infertility.

Gonadotropes are specialized cells of the anterior pituitary gland that produce the gonadotropins, FSH and LH.

Gonadotrophin releasing hormone (GnRH) is a hormone secreted in pulses by the hypothalamus, which stimulates the synthesis of gonadotrophins by the pituitary gland. Gonadotrophins are essential for the development of ovarian follicles (FSH) and for ovulation (LH).

Gonadotropins are protein hormones, the most principal of these being LH and FSH, secreted by the anterior pituitary gland.

Granulosa cells are somatic cells that surround the oocyte, providing it with the physical support and nutrients needed for proper oocyte development.

Growth hormone (GH) is a hormone produced by somatotropes and acts on the liver and adipose tissue to control growth, and the metabolism of lipids, proteins, and carbohydrates.


A gynecologist is a physician who focuses on the health care of women and, in particular, the female reproductive system.