Meoisis (Leaving Cert Biology): Revision Notes

Meiosis

• Meiosis is a type of cell division that reduces the chromosome number by half, producing haploid cells.
• In humans, meiosis occurs in the ovaries and testes, resulting in sperm and egg cells.
• In flowering plants, meiosis produces cells that develop into pollen grains and egg cells.
• In humans, the parent nucleus starts with 46 chromosomes (diploid) and divides to produce daughter cells with 23 chromosomes (haploid).

Functions of Meiosis

1. Production of Gametes:

• Meiosis produces haploid gametes (sperm and egg cells) needed for sexual reproduction.

2. Maintains Chromosome Number:

• Meiosis ensures that sexual reproduction does not increase the chromosome number in offspring.
• Haploid gametes combine during fertilisation to restore the diploid chromosome number.

3. Allows for Variation:

• Meiosis produces cells with different combinations of genes, leading to genetic variation in offspring.
• This variation arises due to crossing over and independent assortment of chromosomes.

Differences Between Mitosis and Meiosis

Mitosis	Meiosis
Maintains the chromosome number in the daughter cells	Halves the number of chromosomes in the daughter cells
Produces genetically identical cells	Produces cells with different combinations of genes (variation)
Involves 1 round of nuclear division	Involves 2 rounds of nuclear division