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Stages of Meiosis

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Queen's University
BIOL 201
Elaine Power

Stages of Meiosis Interphase DNA replicates → Identical sister chromatids form Meiosis I Meiosis II (same as mitosis) Prophase //Spindle forms //Spindle forms Nuclear envelope disappears //Nuclear envelope disappears - Chromosomes shorten/thicken/condense - Form bivalents/tetrads - Crossing-over of homologous pairs Metaphase//Spindle complete //Spindle complete - Bivalents at equator - Chromosomes at equator - Join to spindle (fibres) via centromere Anaphase //Cytokinesis begin //Cytokinesis begins Random segregation of homologues Random segregation of chromatids - Intact centromeres - Chromatids are pulled to opposite poles - Two chromatids on one chromosome - Centromeres divide Telophase //Spindle disappears //Spindle disappears //Nuclear envelope reforms //Nuclear envelope reforms - 2 haploid cells - 4 haploid daughter cells - Chromosomes still duplicated Principles of Mendelian Inheritance  Mendel's 1st Law of Segregation (Anaphase I and II) o During gamete formation, allele pairs (Gg) of one gene separate (G)(g) o Thus, only one of the alleles of one gene is present in a single gamete o Monohybrid inheritance (single gene - 3:1 ratio) o Recessive alleles can cause genetic disorders (e.g. cystic fibrosis)  Mendel's 2nd Law of Independent Assortment (Anaphase I and II) o Alleles for one gene segregate independently with the alleles of another gene (GgBb) o Two genes for each characteristic segregate during gamete production (GB)(gb)(Gb)(gB) o Independent assortment means either G / g can go with either of B / b o Meiosis separates alleles / h
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