Example 1
A species has diploid number 16. How many chromosomes are in its typical gametes and restored zygote?
Gametes are haploid: 216=8. Fusion of two normal gametes gives 8+8=16 in the zygote.
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Year 10
Mitosis, meiosis and chromosome numbers
Identify cell-division outcomes and track chromosome sets through gamete formation and fertilisation.
Method and worked examples
Before cell division, DNA is copied. Mitosis produces two daughter cells that normally retain the parent cell’s chromosome number and inherited information. It supports growth, repair and some asexual reproduction. Meiosis produces haploid cells with one chromosome from each homologous pair, halving the chromosome-set number. In animals these cells become gametes. The two processes have different roles, even though both involve chromosome movement.
Meiosis generates new combinations through the distribution of homologous chromosomes and exchange of DNA between homologues. Fertilisation joins two haploid gametes, restoring the diploid number. In humans, ordinary body cells typically have 46 chromosomes and gametes 23. These numbers are species-specific, not universal. Counting chromosome sets helps prevent the incorrect prediction that chromosome number doubles in every generation.
Example 1
Example 2
A human skin cell divides by mitosis. What chromosome number is expected in each daughter cell?
Each normal daughter cell has 46 chromosomes, matching the parent body cell’s number rather than halving it.
Watch out: Mitosis usually retains chromosome number; meiosis halves it and generates new genetic combinations for sexual reproduction.