Answer: Homologous chromosomes pair up (synapsis).
- A Sister chromatids pairing along their length
- B Homologous chromosomes pair up (synapsis)
- C Non-homologous chromosomes pairing randomly
- D All chromosomes aligning at the spindle equator
Correct answer: B. Homologous chromosomes pair up (synapsis)
Explanation: Bivalent (tetrad): two homologous chromosomes pair up (synapsis) in Prophase I. Each homolog consists of two sister chromatids.
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.