MEIOSIS Lets talk about SEX Scientifically speaking of

MEIOSIS

Let’s talk about SEX! Scientifically speaking, of course…

Vocabulary List • • • Haploid (1 n) Diploid (2 n) Gamete Zygote Somatic Cell Sex Cells • Chromatid • Chromosomes • Homologous Pair • Homologs • Synapsis • Crossing Over

What is a chromsome? “histones” are wound up like rope DNA strands get wrapped around proteins called “histones” DNA “Rope” is twisted and stacked to create chromosomes during Prophase

Gamete a reproductive cell that has only 1 set of chromosomes (1 n) Example: Sperm or Egg Zygote a fertilized egg with 2 sets of each chromosome (2 n)

• Sexual reproduction involves the fusion of male and female gametes. • The resulting cell is called a zygote.

Haploid having 1 copy of each chromosome (1 n) Example: gametes Diploid Having 2 copies of each chromosome (2 n) All other body cells are diploid Example: skin cells or tissue cells

Image of Chromosomes • All of our cells (except gametes) have 2 copies of each chromosome. • One copy of each chromosome is maternal, and the other copy is paternal.

Single Chromatid from the father Duplication Single Chromatid from the mother Duplication

• Homologous Chromosome Pair • 1 from mother and 1 from father • Carry genes for the same trait • Can be different for each chromosome in pair • Example: Eye color (blue vs. brown)

One Homologous Pair of Chromosomes

Meiosis Type of cell division that cuts the number of chromosomes in half – involves 2 divisions: –(meiosis I & meiosis II) – occurs in sex cells • It’s how we get our sex cells

Meiosis starts with 1 diploid cell and produces 4 haploid cells 1 diploid 4 haploid cells

Meiosis II

Meiosis ONE is REDUCTIONAL division

Meiosis I (One) • • Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis • Each phase is the same as Mitosis EXCEPT that homologous chromosomes are separated NOT chromatids

Prophase I Events are the same as prophase in Mitosis • replicated chromosomes condense • spindle apparatus forms & fibers attach to chromosomes • nuclear membrane breaks down • New EVENT for Prophase I synapsis & crossing over occurs

Synapsis when homologous chromosomes pair up

Crossing Over Non-sister chromatids exchange chromosome material Chromatids exchange pieces of chromosome material Each chromatid is different than the other

Metaphase I • Same as Metaphase in Mitosis • Homologous Chromosomes line up along the equator

Anaphase I homologous chromosomes separate & move to opposite poles

Telophase I – spindle apparatus breaks down – chromosomes decondense – nuclear membranes partially reform around two nuclei Cytokinesis usually occurs between meiosis I & II

Meiosis II Each of the 2 cells formed by Meiosis I proceed to Meiosis II • Looks EXACTLY like Mitosis!!! – Prophase II – Metaphase II – Anaphase II – Telophase II and Cytokinesis

Meiosis II Prophase II • chromosomes condense • spindle fibers form & attach to chromosomes • nuclear membrane breaks down Metaphase II • chromosomes line up single-file along equator of spindle

Meiosis II Anaphase II – centromeres part – sister chromatids (now called chromosomes) separate & move toward opposite poles Telophase II – spindle fibers break down – chromosomes de-condense – nuclear membranes reform Cytokinesis divides the 2 cells into 4

How does Meiosis Apply to me? • We all have 46 Chromosomes in each of our somatic (body) cells – Mother’s Egg – produced by Meiosis and has 23 Chromosomes (haploid) – Father’s Sperm – produced by Meiosis and has 23 chromosomes (haploid) • Egg fertilized by Sperm 46 Chromosomes in a zygote (Diploid)