Understanding:
• Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex
In humans, sex is determined by a pair of chromosomes called the sex chromosomes (or heterosomes)
- Females possess two copies of a large X chromosome (XX)
- Males possess one copy of an X chromosome and one copy of a much shorter Y chromosome (XY)
The Y chromosome contains the genes for developing male sex characteristics (specifically the SRY gene)
- In its absence of a Y chromosome, female sex organs will develop
- The sex chromosomes are homologous in females (XX) but are not homologous in males (XY)
Hence the father is always responsible for determining the sex of offspring:
- If the male sperm contains an X chromosome, the growing embryo will develop into a girl
- If the male sperm contains a Y chromosome, the growing embryo will develop into a boy
- In all cases the female egg will contain an X chromosome (as the mother is XX)
The remaining chromosomes in the organism are called autosomes (they do not determine sex)
Sex Determination in Humans (the XY System)
