CELL DIVISION

Cell Division  One cell  Two identical cells  Cells must be able to pass on ALL information from their DNA  So DNA must be replicated before cell division occurs

Prokaryotic Cells  No nucleus  DNA is found as circular molecule  BINARY FISSION DNA replicates DNA replicates DNA attaches to membrane DNA attaches to membrane Cell pinches & splits Cell pinches & splits

Eukaryotic Cells  Much more complicated  Chromosome – DNA coiled around proteins

Formation of chromosomes  DNA at “rest” found unorganized in nucleus  Just before cell division, it organizes itself into chromosomes

Human Chromosomes

Parts of a Chromosome

UNDERSTANDING CHECK

How many do humans have?  Somatic cells = DIPLOID (2n) 46 chromosomes (23 pairs) 46 chromosomes (23 pairs) 22 pairs = Autosomes 22 pairs = Autosomes 1 pair = Sex chromosomes (X & Y) 1 pair = Sex chromosomes (X & Y) XX (female) vs. XY (male) XX (female) vs. XY (male)

Human Karyotype

UNDERSTANDING CHECK

How many do humans have?  Gametes = HAPLOID (n) Formed from germ cells Formed from germ cells 23 chromosomes (one of each) 23 chromosomes (one of each) Sperm + Egg = Zygote  YOU! Sperm + Egg = Zygote  YOU! = = 46

Haploid + Haploid = Diploid

Cell Cycle

 G1 – 1 st Growth – Routine functions  S – Synthesis – DNA Replication  G2 – 2 nd Growth – Prepare to Divide  M – Mitosis – Division of the Nucleus  C – Cytokinesis – Division of the Cytoplasm  MOVIE MOVIE

UNDERSTANDING CHECK

Cell Cycle  Numerous ways to control speed  Malfunction of cell cycle = cancer

Interphase  Includes the G1, S, & G2 phases  When the cell is not dividing or “at rest”  DNA is found unorganized in the nucleus

Interphase

Mitosis  Division of the nucleus to form 2 identical nuclei  Chromosome = 2 identical chromatids 2 identical chromatids (formed after replication) (formed after replication)

UNDERSTANDING CHECK

Mitosis  Prophase  Metaphase  Anaphase  Telophase  MOVIE 1 MOVIE 1 MOVIE 1  MOVIE 2 MOVIE 2 MOVIE 2

Prophase  Chromosomes become visible  Nuclear envelope dissolves  Spindle forms from centrioles

Prophase

Metaphase  Chromosomes line up along equator

Anaphase  Chromatids separate and reeled to opposite poles

Telophase  Nuclear envelope forms at each pole  Chromosomes uncoil  Spindle dissolves  Cytokinesis begins

Telophase

UNDERSTANDING CHECK

Cytokinesis  Division of the cytoplasm  Animal cells – pinch and split  Plant cells – forms cell plate down the center  MOVIE MOVIE

Meiosis  Formation of haploid gametes from one germ cell  Homologous chromosomes – chromosomes of similar size, shape, & genetic content

Meiosis  Meiosis I Prophase I Prophase I Metaphase I Metaphase I Anaphase I Anaphase I Telophase I Telophase I  Meiosis II Prophase II Metaphase II Anaphase II Telophase II

Prophase I  Homologous chromosomes pair up & crossing over occurs  Animation Animation  Allows genetic variation variation

Prophase I  Chromosomes become visible become visible  Nuclear env. breaks down breaks down  Spindle forms  Crossing over

Metaphase I  Pairs of homologous chromosomes move to equator of cell

Anaphase I  Homologous chromosomes reeled to opposite poles

Telophase I  Chromosomes gather at poles  Cytokinesis

Prophase II  New spindle forms

Metaphase II  Chromosomes line up on equator

Anaphase II  Chromatids reeled to opposite poles

Telophase II  Nuclear envelope forms  Cytokinesis

Meiosis

UNDERSTANDING CHECK

What can go wrong?  Nondisjunction – the chromosomes fail to separate during meiosis  Trisomy – individual has 3 of a particular chromosome  Down syndrome = trisomy 21

UNDERSTANDING CHECK

Meiosis in Males

Meiosis in Females