Topic 10: Meiosis

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Essential Idea: Meiosis leads to independent assortment of chromosomes and unique composition of alleles in daughter cells

Interphase: chromosomes replicate; before meiosis

DNA is replicated during the S phase

If DNA is not replicated, there's no purpose for meiosis II

One benefit of the duplication of chromatids is that it increases the potential for genetic recombination to occur

Meiosis I: a reduction division (diploid -> haploid); homologous chromosomes are separated

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Meiosis II: separates sister chromatids (may not be identical if crossing over occurred)

Final outcome of meiosis: 4 haploid daughter cells

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Random Assortment: Independent assortment of genes due to random orientation of pairs of homologous chromosomes in meiosis I

Independent Assortment: Inheritance of one gene/trait is independent to that of any other

Homologous chromosomes line up at equator as bivalents; orientation is random

Linked Genes: Independent assortment will NOT occur if two genes are located on the same chromosome

Chiasmata: formation between non-sister chromatids can result in the exchange of alleles

Synapsis: during PI, homologous chromosomes become connected by the synaptonemal complex

*While autosomes always undergo synapsis during meiosis, sex chromosomes often remain unpaired

Chiasmata hold the chromosomes together as a bivalent until AI

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Crossing Over: the exchange of DNA material between non-sister homologous chromatids

The chromosomes that consist of genetic material from both homologues are called Recombinant Chromosomes

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Essential Idea: Genes may be linked or unlinked and are inherited accordingly

Unlinked genes segregate independently as a result of meiosis

Independent segregation = greater number of potential gamete combinations/possible phenotypes

Gene loci are linked if on same chromosome

Linked genes may be separated due to recombination