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Meiosis and chromosome number explained

Inheritance, variation and evolution • Reproduction

Key concepts

What you'll likely be quizzed about

  • Diploid cells contain two matching sets of chromosomes, one inherited from each parent.
  • For example, human diploid cells have 23 pairs or 46 chromosomes.
  • In contrast, gametes are haploid, containing a single set of chromosomes (23 in humans).
  • Halving the chromosome number in gametes prevents doubling at every generation and maintains a stable chromosome number during sexual reproduction.

Flashcards

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Why meiosis halves chromosome number

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Two divisions after one DNA replication separate homologous chromosomes and sister chromatids, giving each gamete one copy of each chromosome.

Key notes

Important points to keep in mind

Meiosis involves one DNA replication followed by two cell divisions that halve chromosome number.

Haploid gametes restore diploid number upon fusion during fertilisation.

Crossover and independent assortment promote genetic variation among gametes.

Mitosis produces two identical diploid cells; meiosis yields four non-identical haploid cells.

Meiosis occurs exclusively in reproductive organs with varying timing in males and females.

Chromosome number varies among species; humans possess 23 pairs in diploid cells.

Incorrect segregation leads to abnormal chromosome numbers and developmental challenges.

Remember the sequence: replicate, pair and segregate homologues, separate sister chromatids.

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