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Meiosis and reproduction
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Why do children look like their parents, but not exactly? The answer lies in meiosis and sexual reproduction.
Gametes are haploid
Gametes (sperm and egg cells) have half the normal number of chromosomes. They are haploid.
In humans a gamete has 23 chromosomes. At fertilisation they join to make a diploid cell with 46.
In humans a gamete has 23 chromosomes. At fertilisation they join to make a diploid cell with 46.
Meiosis
Meiosis is the cell division that makes gametes.
The cell divides twice, making four cells.
Each is haploid and genetically different from the others.
The cell divides twice, making four cells.
Each is haploid and genetically different from the others.
Sexual and asexual reproduction
Sexual: two parents, gametes fuse, offspring vary. Variation helps a species survive changes.
Asexual: one parent, mitosis only, offspring are identical clones. It is fast and needs no partner.
Asexual: one parent, mitosis only, offspring are identical clones. It is fast and needs no partner.
A dog body cell has 78 chromosomes. How many are in a dog sperm cell?
- Sperm cells are gametes, made by meiosis.
- Gametes are haploid, with half the number.
- 78 ÷ 2 = 39
Answer: 39 chromosomes
Meiosis divides twice to make four genetically different haploid gametes. Fertilisation restores the diploid number. Sexual reproduction gives variation; asexual gives clones.
The interactive lesson includes the diagrams for this topic.
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