MEOSIS

• MEIOSIS

  DEFINITION:

  • A type of cell division that results in
  • four daughter cells
  • each with half the number of chromosomes of the parent cell,
  • production of gametes
  • 4 haploid
  • • TWO DIVISIONS:
  • Meiosis I
  • Meiosis II
• MEIOSIS I

  • PROPHASE I
  • METAPHASE I
  • ANAPHASE I
  • TELOPHASE I

  A) PROPHASE I

  B) CROSSING OVER

  C) METAPHASE I

  D) CENTROMERE

  E) ANAPHASE I

  F) TELOPHASE I

  G) CYTOKINESIS I

  
• INTERPHASE I

  • Similar to mitosis interphase
  • sister chromosomes replicate (s phase)
  • Each duplicated chromosome consist of two identical sister chromatids attached at their centromeres.
  • Centrioles pairs also replicate.

  A) CHROMATIN

  B) CENTRIOLES

  C) NUCLEOLUS

  D) NUCLEAR ENVELOPE

  
• PROPHASE I

  • Longest and most complex phase (90%)
  • Chromosomes condense
  • Synapsis occurs:
  • homologous chromosomes come together to form a tetrad.
  • Also called crossing over
  • Tetrad is two chromosomes or four chromatids.

  A) HOMOLOGOUS PAIR

  B) CROSSING OVER

  C) GAMETES

  
• PROPASE I

  A) SPINDLE

  B) HOMOLOGOUS

  
• STAGES OF PROPHASE I

  A) LEPTOTENE

  B) ZYGOTENE

  C) PACHYTENE

  D) DIPLOTENE

  E) DIAKINESIS

  F) CONDENSE

  G) SYNAPSIS

  H) CROSSING OVER

  I) BIVALENT

  
• METAPHASE I

  • Shortest phase
  • Tetrads align on the metaphase plate.
  • Independent assortment occurs:
  • Orientation of homologous pair to poles is random

  A) TETRADS

  B) EQUATORIAL PLATE

  
• ANAPHASE I

  • Homologous chromosomes separate and move towards the poles.
  • Sister chromatids remain attached at their centromeres..

  A) CHROMOSOME

  
• TELOPHASE I

  • Each pole now has haploid set of chromosomes.
  • Cytokinesis occurs and two haploid daughter cells are formed.

  
• MEIOSIS I

  A) INTERPHASE

  B) PROPHASE I

  C) METAPHASE I

  D) ANAPHASE I

  E) TELOPHASE I

  F) CYTOKINESIS I

  
• MEIOSIS II

  • Prophase II
  • Metaphase II
  • Anaphase II
  • Telophase II

  
• PROPHASE II

  • Chromosomes coil and become compact(if uncoiled after telophase 1)
  • Nuclear envelope and nucleolus, if reformed, disappears again.
  • Centriole move to opposite poles, forming spindle fibers between them

  A) CENTRIOLES

  B) SPINDLE FIBERS

  
• METAPHASE II

  • Individual duplicated chromosomes align on the equator.
  • One chromosome per spindle fiber attached by means of kinetochore of centromere.
  • Centriole has reached the poles

  
• ANAPHASE II

  • Spindle fibers contract.
  • Duplicated chromosomes split in half (centromere dividing in two.
  • Sister chromatids separate and move to opposite poles.

  
• TELOPHASE II

  • Daughter chromosomes has reached the poles.
  • Two cells invaginate and form 4 daughter haploid cells (gametes)
  • They uncoil and form chromatin.
  • Nuclear envelope and nucleolus form around chromatin again.
  • Centrioles form centromere.

  A) FOUR HAPLOID DAUGHTER CELLS

  
• STAGES OF MEIOSIS II

  A) PROPHASE II

  B) METAPHASE II

  C) ANAPHASE II

  D) TELOPHASE II

  E) CYTOKINESIS II

  
• RESULT OF MEIOSIS

  • Gametes (egg and sperm form)
  • Four haploid cells (n) with one copy of each chromosome
  • One allele of each gene
  • Different combinations of alleles for different genes along the chromosome.

  
• EASIEST WAY TO REMEMBER THE STAGES:

  • P - PREPARATION
  • M - MIDDLE
  • A - AWAY
  • T - TWO
• MEIOSIS II

  A) PROPHASE II

  B) METAPHASE II

  C) ANAPHASE II

  D) TELOPHASE II

  E) CYTOKINESIS II

  F) 4 HAPLOID DAUGHTER CELL