🧬 Role of Sex Chromosomes in Sex Determination
This lesson helps students understand the role of sex chromosomes in sex determination with clear explanations of X and Y chromosomes, the fertilisation process, and exam-oriented biology notes for NEB and SEE students.
🧑🤝🧑 What are Sex Chromosomes?
Humans have 46 chromosomes in total, or 23 pairs.
Out of these:
22 pairs are called autosomes (control body traits)
1 pair is called the sex chromosome pair, which determines the biological sex of the individual.
👩🔬 Types of Sex Chromosomes:
X chromosome
Y chromosome
Each human inherits one sex chromosome from each parent.
🧫 Chromosomal Combinations:
| Chromosome Pair | Result | Sex |
|---|---|---|
| XX | Female | 👧 |
| XY | Male | 👦 |
🔄 How Does Sex Determination Happen?
The mother always contributes an X chromosome (because she has XX).
The father can contribute either an X or a Y chromosome (because he has XY).
So:
X (from mother) + X (from father) = XX (Girl)
X (from mother) + Y (from father) = XY (Boy)
➡️ Hence, the father determines the sex of the child, not the mother.
🧪 Summary Points:
Sex chromosomes are XX (female) and XY (male).
The 23rd chromosome pair determines the sex of a human.
Male gametes (sperms) can carry either X or Y.
Female gametes (eggs) always carry X.
50% chance of having a boy or a girl in each pregnancy.
🔍 Real-Life Importance:
Helps in understanding genetic disorders like Turner syndrome (XO) or Klinefelter syndrome (XXY).
Used in DNA testing, forensics, and parental determination.
Key in fields like genetics, biology, and medicine.