Principle of Independent Assortment

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4 unique types of gamete possible due to the Principle of Independent Assortment of Meiosis I.
During metaphase of meiosis I, synapsed pairs of homologous chromosomes (known as bivalents or tetrads) are lined up on an imaginary plane in the middle of the cell called the metaphase plate. The chromosomes are attached to spindle fibres at their centromeres. The spindle fibres align the homologous chromosomes on the metaphase plate. Pairs of homologous chromosomes (tetrads) are lined up independently of each other (maternal and paternal chromosomes are also lined up on the metaphase plate at random). Subsequently anaphase of Meiosis I proceeds; centromeres divide resulting in the bivalents separating and the homologs moving to separate poles of the cell as the spindle fibres contract. Due to the alignment process that occurs at random during metaphase I, there is a chance of 4 genetically different gametes being produced at the end of meiosis. Each unique possible gamete has a probability of 1/4 of being formed[1].

Metaphase, and anaphase of Meiosis I are responsible for Gregor Mendel's Principles of: segregation and independent assortment respectively.

References

  1. Freeman (2008) Biological Science, 3rd edition, San Francisco: Pearson. p 275
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