Chapter 6 Chromosomes and Cell Reproduction Section 1

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 I. New Cells formed by Division • 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.

Section 6. 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 New membrane pinching inward DNA

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. Mosquito 6 Garden pea 14 Saccharomyces (yeast) 18 Corn 20 human 46 Dog 78 Adder’s tongue fern 1, 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 carry information that determines an organism’s gender. Either X or Y • Human gametes are haploid, with 23 chromosomes. • 1 copy of the parents DNA 2 sex cells converge and make a diploid cell

Section 1 How Chromosome Number and Structure Affect Development 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 6. 2 -6. 3 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: G 2 phase Replicated DNA and cell prepare for cell division. Microtubules in the centrioles form to move DNA

G 2 check point: DNA Synthesis • DNA replication is checked for typo’s in sequence and repaired by enzymes. • If DNA sequence passes inspection 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

Anaphase End telophase/cytokenisis Prophase Metaphase