CELL DIVISION Cell Division One cell Two identical

CELL DIVISION

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

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

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

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

Human Chromosomes

Parts of a Chromosome

UNDERSTANDING CHECK

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

Human Karyotype

Human Karyotype

UNDERSTANDING CHECK

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

Haploid + Haploid = Diploid

Cell Cycle

Ø G 1 – 1 st Cell Cycle Growth – Routine functions Ø S – Synthesis – DNA Replication Ø G 2 – 2 nd Growth – Prepare to Divide Ø M – Mitosis – Division of the Nucleus Ø C – Cytokinesis – Division of the Cytoplasm Ø MOVIE

UNDERSTANDING CHECK

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

Interphase Ø Includes the G 1, S, & G 2 phases Ø When the cell is not dividing or “at rest” Ø DNA is found unorganized in the nucleus

Interphase

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

UNDERSTANDING CHECK

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

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

Prophase

Metaphase Ø Chromosomes line up along equator

Anaphase Ø Chromatids separate and reeled to opposite poles

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

Telophase

UNDERSTANDING CHECK

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

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

Meiosis Ø Meiosis I Prophase I l Metaphase I l Anaphase I l Telophase I l Ø Meiosis II Prophase II l Metaphase II l Anaphase II l Telophase II l

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

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

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

Anaphase I Ø Homologous chromosomes reeled to opposite poles

Telophase I Ø Chromosomes gather at poles Ø Cytokinesis

Prophase II Ø New spindle forms

Metaphase II Ø Chromosomes line up on equator

Anaphase II Ø Chromatids reeled to opposite poles

Telophase II Ø Nuclear envelope forms Ø Cytokinesis

Meiosis

UNDERSTANDING CHECK

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

UNDERSTANDING CHECK

Meiosis in Males

Meiosis in Females