Sex determination

Sex determination is the biological process by which an organism develops as a particular sex. It can depend on chromosomes, genes, hormones, environmental conditions, or combinations of these factors.

Sex-determination system: A biological mechanism that assigns or influences sex, such as chromosomal, genic, or environmental determination. This broader framework distinguishes the different routes that initiate sexual development.
Sex chromosome: A chromosome that carries genes involved in sex determination or sex-linked inheritance. Sex chromosomes provide one common source of the signals that initiate development.
XY sex-determination system: A system in which individuals with two X chromosomes typically develop as female and those with X and Y typically develop as male. It is a familiar chromosomal pattern, though genes and development influence its outcomes.
Drosophila sex determination: The fruit fly developmental system in which the ratio of X chromosomes to autosomes helps regulate sexual differentiation. Fruit flies use a genetic mechanism unlike the mammalian Y-chromosome trigger.
SRY: A gene on the Y chromosome that commonly initiates testis development in mammals. Its activity is a pivotal genetic trigger in the common mammalian pathway.
Gonad: A reproductive organ, such as an ovary or testis, that produces gametes and hormones. Gonads develop in response to early signals and then shape further differentiation.
ZW sex-determination system: A system in which females typically carry ZW chromosomes and males carry ZZ chromosomes. Birds and some other animals use this arrangement instead of the common mammalian XY pattern.
Bird sex determination: Sex determination in birds, typically based on female ZW and male ZZ chromosome patterns. Birds provide a prominent example of the ZW system and its distinct inheritance pattern.
SOX9: A transcription factor that promotes testis development and supports male sexual differentiation in mammals. It acts downstream of SRY and helps stabilize the testis-development pathway.
Sexual differentiation: The development of sex-related anatomical, physiological, and behavioral traits. Determination initiates pathways whose outcomes emerge through this broader developmental process.

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