Fertilization
The diploid chromosome number is restored at fertilization when two very different gamete nuclei
fuse to form the zygote.
The variation present at fertilization is from three sources:
- Crossing over that occurs during prophase I.
- Random alignments at metaphase I that lead to millions of combinations of maternal and paternal
chromosomes in each gamete.
- Of all the genetically diverse gametes produced, chance will determine which two will meet.
How Mitosis and Meiosis Differ
- Mitotic cell division produces identical cells (clones). This type of division is common in
single-celled, asexually reproducing organisms and in the growth process of multicelled forms.
- Meiosis occurs only in the germ cells used in sexual reproduction. It gives rise to novel
combinations of alleles in offspring.
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