1. Ch 6 – Chromosomes &
Cell Reproduction

2. Binary Fission Used by bacteria to divide or reproduce Two steps
1 – DNA is copied
2 – Cell divides by adding membrane between 2 DNA copies

3. Chromosomes After DNA is copied it forms chromosomes
DNA wraps around proteins & supercoils
Chromatids = two exact copies
Centromere = attachment between chromatids

4. Homologous Chromosomes
Similar chromosomes (pairs)
23 pairs = 2 sets of 23
1 set from each parent
22 pairs of autosomes
1 pair of sex chromosomes
XY = male
XX = female

5. Karyotypes
Picture of all chromosomes arranged by size and matched with their partner / homologue

6. Haploid = 1 set of chromosomes Sperm and egg cells only (gametes)
Diploid = 2 sets of chromosomes
All other cells (somatic)
Somatic cell karyotype
Sperm cell karyotype

7. The Cell Cycle

8. The Cell Cycle Interphase: time between divisions G1 Phase = growth
S Phase = DNA is copied
G2 Phase = prepares to divide, checks DNA
Mitosis = division of nucleus
Cytokinesis = division of cell

9. Mitosis
4 Steps ….

10. Prophase Chromosomes coil up and become visible
Nuclear envelope dissolves
Spindle forms

11. Metaphase Chromosomes line up in center of cell
Spindle fibers link chromatids to poles

12. Anaphase Spindle fibers shorten
Chromatids are pulled to opposite poles

13. Telophase Nuclear envelopes form around chromosomes at each pole.
Chromosomes uncoil
Spindle dissolves

14. Cytokinesis Cytoplasm divided in half
Membrane grows and pinches in to enclose each new cell
Result = two genetically identical cells