Meiosis

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What is Meiosis?

Meiosis is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production gametes and plant spores.

Stages

  • In Prophase 1, homologous pairs become attached to each other. Crossing over occurs.
  • In Metaphase 1, the tetrads line up in the middle of the cell.
  • In Anaphase 1, the tetrads separate and the paired chromatids move along the spindle to their respective centrioles.
  • In Telophase 1, nuclear membranes enclose the separated chromatids. The first meiotic division ends, leaving with two separate cells.
  • In Prophase 2, homologous chromatids separate.
  • In Metaphase 2, the chromatids line up in the middle of the cells.
  • In Anaphase 2, the separated chromatids approach their respective poles. Division begins again.
  • In Telophase 2, nuclear membranes completely enclose the separated chromatids once more. We are left with four cells.

Diploid vs Haploid

Diploid cells contain both chromosomes that code for a trait.

Haploid cells contain only one chromosome that code for a trait.

Chromosomes

Human cells commonly contain 23 pairs of chromosomes, which gives us 46 chromosomes altogether. Each chromosome codes for a different gene; for example, the 23rd chromosome codes for sex. Having more or less than 46 chromosomes typically results in a genetic issue: people with an extra 21st chromosome are born with Down Syndrome.