Summary
The SRY gene on the Y chromosome triggers male development in mammals.
In depth
SRY triggers Sertoli cells, testis development and anti-Müllerian hormone; testosterone leads to male internal and external genitalia. Without SRY, ovaries form. Chromosomal sex and phenotype may differ in conditions like androgen insensitivity.
Gonads are initially bipotential. SRY activates SOX9; without SRY, WNT4 and FOXL2 favour ovaries. Hormones then shape duct systems and external genitalia.
Example: androgen insensitivity syndrome gives XY individuals with female external features.
In mammals, chromosomal sex is set at fertilisation: XX is female and XY male. The SRY gene on the Y chromosome encodes a transcription factor that switches on SOX9, causing the bipotential gonad to form testes, which secrete anti-Mullerian hormone (removing female ducts) and testosterone (maintaining male structures).
Without SRY, the gonad forms ovaries. Other systems differ: birds have ZW females and ZZ males, many reptiles use temperature (in turtles warm nests often give females), and some fish change sex. Disorders of sex development arise from variants in these pathways.
Example: a person with XY chromosomes and androgen insensitivity develops a female body.
Remember: chromosomal, gonadal and phenotypic sex can differ.
Frequently asked questions
What is Sex Determination?
The SRY gene on the Y chromosome triggers male development in mammals.
Which area of biology covers Sex Determination, and how advanced is it?
Sex Determination is one of the 54 topics in Developmental Biology. It is rated Intermediate, so it suits learners who already know the core vocabulary. Related topics in this area include Apoptosis in Development, Metamorphosis in Amphibians, Preimplantation Genetic Testing.
Can you give an example of Sex Determination?
Some reptiles determine sex by egg temperature.
What should I learn before Sex Determination?
Work through the Beginner topics in Developmental Biology first, such as Fertilisation, Zygote, Embryo, then return to Sex Determination. Intermediate topics assume the Beginner vocabulary.
What topics are related to Sex Determination?
The closest topics to Sex Determination are Apoptosis in Development, Metamorphosis in Amphibians, Preimplantation Genetic Testing, Notch Signalling. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand Sex Determination?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Sex Determination. To practise the whole of Developmental Biology, use the Developmental Biology quiz.
How is Sex Determination different from Apoptosis in Development?
Sex Determination: The SRY gene on the Y chromosome triggers male development in mammals. Apoptosis in Development: Programmed cell death sculpts tissues, such as separating fingers and toes. Read both side by side and note what each one explains.
How should I study Sex Determination step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Apoptosis in Development and explain the difference aloud. Finally, take the Developmental Biology quiz and come back to this page for any question you miss.