Chapter 6 Chromosomes and Cell Reproduction Section 1: Chromosomes Section 2: The Cell Cycle Section 3: Mitosis and Cytokinesis

Section 1 Chromosomes Objectives: Identify four examples of cell division in eukaryotes and one example in prokaryotes. Differentiate between a gene, a DNA molecule, a chromosome, and a chromatid. Differentiate between homologous chromosomes, autosomes, and sex chromosomes. Compare haploid and diploid cells. Predict how changes in chromosome number or structure can affect development.

6.1 chromosomes Cells divide or reproduce –In humans, about 2 trillion/day 1.DNA is copied and then distributed to each new cell 2.Different processes occur in prokaryotes vs. eukaryotes. I. New Cells formed by Division

Section6.1 Function of Cell Division allows organisms to reproduce asexually grow replace worn-out or damaged tissue form gametes.

Prokaryotic Cell Reproduction Bacteria reproduce asexually by binary fission, a process that produces identical offspring. –Stage 1: DNA copied –Stage 2: Cell divides by adding new membranes and eventually pinching off into 2 new cells. –The 2 new cells contain the same DNA and are identical to each other DNA New membrane pinching inward

Bacteria cell dividing

Eukaryotic Cell Reproduction Before eukaryotic cell division, DNA coils tightly around proteins and forms chromosomes. At cell division, each chromosome consists of two chromatids attached at the centromere.

Section 1 How Chromosome Number and Structure Affect Development Sets of Chromosomes Each organism has a characteristic number of chromosomes. Mosquito6 Garden pea14 Saccharomyces (yeast)18 Corn20 human46 Dog78 Adder’s tongue fern1,2 62

Types of chromosomes 2 basic types: –Sex chromosomes(2) and Autosomes(44) A little chomosome vocabulary diploid= cells having 2 sets of chromosomes Haploid= cells having 1 set of chromosomes Homologous= autosomes are homologues, meaning they are the same shape, size and carry the genes for the same traits.

Sets of chromosomes Human somatic cells or autosomes –are diploid (2 sets of chromosomes) –totaling 46 homologous chromosomes 23 chromosomes from each parent

Sex Chromosomes Human gametes are haploid, with 23 chromosomes. 1 copy of the parents DNA 2 sex cells converge and make a diploid cell carry information that determines an organism’s gender. Either X or Y

Section 1 Change in Chromosome Number Karyotypes are used to examine an individual’s chromosomes and identify possible abnormalities in chromosome number. can cause abnormal development or be fatal. How Chromosome Number and Structure Affect Development

tests are used to make karyotypes in unborn children Amniocentesis (amniotic fluid) chorionic villi sampling(placenta)

Triosomy: more than 2 copies of chromosomes normal Down’s syndrome

Change in Chromosome Structure Mutations can cause abnormal development. Deletion: missing genes Piece breaks off Usually fatal Duplication: repeated genes Fragment attaches to homologous chromosome Carries 2 copies Inversion: genes out of order Attaches to same chromosome in reverse order Translocation: genes relocated in wrong place Reattaches to nonhomologous chromosome

Section The Cell Cycle Objectives: Identify the major events that characterize each of the five phases of the cell cycle. Identify the major events of mitosis and cytokenisis Describe how the cell cycle is controlled in eukaryotic cells. Relate the role of the cell cycle to the onset of cancer.

Section 6.2 The Cell Cycle The Life of a Eukaryotic Cell The Cell Cycle has 3 main stages/phases interphase mitosis cytokinesis.

Section 2 Control of the Cell Cycle Cell Checkpoints The cell cycle is carefully controlled through three main checkpoints.: cell growth (G 1 ) checkpoint, DNA synthesis (G 2 ) checkpoint, mitosis checkpoint. When Control is Lost: Cancer Failure of control of cellular growth and division can result in cancer.

Interphase: G 1 phase A cell spends 90 % of its time in interphase. Interphase consists of 3 phases –G 1 phase or growth phase Cells grow and mature Carries out normal functions

G 1 Check point: Cell Growth Decides if the cell will grow or not If OK, then cell goes into S phase and divides normally If NOT OK, then cell goes into resting period( G 0 pahse) cells can reactivate when conditions change or stay here permamnently

Interphase: S phase DNA synthesis (replication) occurs Each chromosome consists of 2 chromatids attached by a centromere

Interphase: G2 phase Replicated DNA and cell prepare for cell division. Microtubules in the centrioles form to move DNA

G2 check point: DNA Synthesis DNA replication is checked for typo’s in sequence and repaired by enzymes. If DNA sequence passes inspection then the proteins made trigger mitosis

M Phase: Mitosis A cell about to divide enters the mitosis or M phase. –Mitosis has 4 stages of division prophase metaphase anaphase telophase

Prophase Chromosomes become visible Nuclear envelope dissolves Spidles form

Metaphase Chromosomes line up along equator of cell Spindle fibers link to the chromatids of each chromosome to opposite poles

Anaphase Centromeres divide Chromatides (now called chromosomes) move toward opposite poles

End of anaphase 2 cells at the end of anaphase. Chromosomes have been pulled to the opposite poles in these plant cells

Telophase Nuclear envelope forms at each pole Chromosomes uncoil Spindles disolve Cytokenisis begins if cell passes check point

Mitosis check point Triggers exit from mitosis Cells go into cytokinesis and then into G 1 phase of cellular growth

Last step: Cytokenesis Cytoplasm of the cell divided in half. –Plant cell: cell plate forms –Animals: protein threads pinch cell in half The cell membrane/wall grows to enclose each cell Forming 2 new identical cells

Metaphase Prophase Anaphase End telophase/cytokenisis