Lesson 2 ·Class 10 · Genetics — Some Basic Fundamentals · Flow Lab
Sex Determination
Why it is the father who decides.
All eggs are alike. The sperms are not — and that is what settles it.
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🧬 Step 1 of 7 · 46 chromosomes, 23 pairs
Of the 23 pairs, 22 pairs are autosomes and the 23rd pair are the sex chromosomes.
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Blaming a mother for the sex of her child has no basis in biology at all — every egg she can make carries an X.
What this lesson covers
Challenges to clear
- Advance to the step that shows why the father decides.
- Step through the whole explanation.
The task
All eggs are alike. The sperms are not — and that is what settles it.
What this lesson covers
- 46 chromosomes, 23 pairs — Of the 23 pairs, 22 pairs are autosomes and the 23rd pair are the sex chromosomes.
- The mother is XX — A woman has two X chromosomes. Every egg she makes therefore carries one X — all eggs are alike.
- The father is XY — A man has one X and one Y. The Y is much smaller than the X.
- Two kinds of sperm — Half his sperms carry X and half carry Y — 50% of each kind.
- X sperm → daughter — If the egg (X) is fused by an X-bearing sperm, the combination is XX and the child produced is a female.
- Y sperm → son — If the egg (X) is fused by a Y-bearing sperm, the combination is XY and the child produced is a male.
- Simply a matter of chance — Which sperm reaches the egg first is pure chance. The mother contributes an X either way, so the sex of the child is determined by the father's sperm — never by the mother.
Hint
Blaming a mother for the sex of her child has no basis in biology at all — every egg she can make carries an X.