Answer: Missing X chromosome (monosomy X: nondisjunction).
- A An extra X chromosome present in the karyotype
- B Missing X chromosome (monosomy X: nondisjunction)
- C An extra Y chromosome present in the karyotype
- D Trisomy of chromosome 21 (Down syndrome)
Correct answer: B. Missing X chromosome (monosomy X: nondisjunction)
Explanation: Turner syndrome: females with 45,X (one X chromosome instead of two). Caused by nondisjunction. Short stature, infertile, no secondary sexual development.
The cell cycle: G1 (growth and preparation), S (DNA replication, chromosome number stays 2n but DNA content doubles), G2 (final checks before division), and M (mitosis itself) - together, G1+S+G2 make up interphase.
Concept context
Mitosis and meiosis: how cells divide for growth, repair, and reproduction.