Cell Division - Meiosis

Mitosis and Meiosis

Progeny

Mitosis 2 Daughter cells identical to parent (diploid)

Meiosis Germ cell division (haploid)

• Reductive division
• Generates haploid gametes (egg, sperm)
• Each genetically distinct from parent

• Genetic recombination (prophase 1)
  • Exchanges portions of chromosomes maternal/paternal homologous pairs
• Independent assortment of paternal chromosomes (meiosis 1)

Cell Birth - Mitosis and Meiosis 1st cell division- Meiosis

Homologous chromosomes pairing unique to meiosis

• Each chromosome duplicated and exists as attached sister chromatids before pairing occurs
• Genetic Recombination shown by chromosomes part red and part black
  • chromosome pairing in meiosis involves crossing-over between homologous chromosomes

(For clarity only 1 pair of homologous chromosomes shown)

Comparison of Meiosis/Mitosis

• After DNA replication 2 nuclear (and cell) divisions required to produce haploid gametes
• Each diploid cell in meiosis produces 4 haploid cells (sperm) 1 haploid cell (egg)
• Each diploid cell mitosis produces 2 diploid cells

Abnormalities

Meiotic Nondisjunction

• Occurs when homologues fail to separate during meiotic division I or II
• Down Syndrome
• Caused by an extra copy of chromosome 21

Nondisjunction

Chromosomal Translocations

• Philadelphia chromosome
• Chronic myelogenous leukemia
  • Piece of Chr9 exchanged with Chr22 Generates truncated abl

Overstimulates cell production

Meiosis Sex Differences

Female (oogenesis)

• Meiosis initiated once in a finite population of cells
• 1 gamete produced / meiosis
• Completion of meiosis delayed for months or years
• Meiosis arrested at 1st meiotic prophase and reinitiated in a smaller population of cells
• Differentiation of gamete occurs while diploid in first meiotic prophase
• All chromosomes exhibit equivalent transcription and recombination during meiotic prophase

Male (spermatogenesis)

• Meiosis initiated continuously in a mitotically dividing stem cell population
• 4 gametes produced / meiosis
• Meiosis completed in days or weeks
• Meiosis and differentiation proceed continuously without cell cycle arrest
• Differentiation of gamete occurs while haploid after meiosis ends

Sex chromosomes excluded from recombination and transcription during first meiotic prophase

References

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Cite this page: Hill, M.A. (2024, April 16) Embryology Cell Division - Meiosis. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Cell_Division_-_Meiosis

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© Dr Mark Hill 2024, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G