Read Sex Determination across Animal Groups
Sex-determination systems differ in which parent produces unlike gametes and how chromosome sets combine.
Sex Determination is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Compare chromosome systems
Humans and Drosophila use XX females and XY males. Grasshoppers often use XX females and XO males, so males have one fewer chromosome. Birds use ZZ males and ZW females; the heterogametic egg determines offspring sex.
Track gametes and ploidy
In humans, X⁻ and Y-bearing sperm occur with roughly equal probability. Honeybee drones develop from unfertilised haploid eggs; a drone has no father and produces no sons. Henking’s X-body is a sex chromosome.
Include non-chromosomal influence
Hormones and environmental conditions can also affect sex determination in some organisms.
OlympIQ exam lens
- ✓Male heterogamety: sperm determines XX/XY.
- ✓Grasshopper male XO; female XX.
- ✓Bird female ZW; egg determines sex.
- ✓Honeybee male: haploid, unfertilised egg.
Identify the heterogametic sex before deciding which gamete determines offspring sex.
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