I. Evidence for Evolutionary Theory

C. Biogeography• Geographic distribution reflects ancestral

relationships• Ex: Nearly all living marsupials restricted to

Australia and nearby islands• Ex: Oldest horse fossils in North America

D. Fossil Record• Appearance, location, time of extinct species• Some evolutionary intermediates

Fig. 22.16

Fig. 22.20

I. Evidence for Evolutionary Theory

D. Fossil Record1. Biases

a. Not all organisms fossilized equally (jellyfish vs. fish)

b. Fossil-bearing rocks typically form from fine sediments (species away from fine sediments preserved less frequently)

c. Tropical rain forest species decompose rapidly before fossilizing

• Fossil record biased toward organisms with hard parts living in aquatic or arid terrestrial environments

II. Chromosomes

• Composed of DNA + Proteins

• When cell not dividing, DNA in chromatin (long, thin strands – 2 m per human cell)

• Chromosomes condense during cell division

• Humans: 23 pairs with 30-70,000 genes

• Other species: 2 (roundworm) -1000+ (fern) chromosomes

Fig. 12.5

Fig. 12.4

III. Cell Cycle

• Growth Stop or Divide• One cycle = generation time

• Typically 8-20 hrs• Some cells never/rarely divide at maturity (nerve, muscle,

erythrocytes)

A. M Phase (Mitotic Phase)• Cell division• Shortest part of cell cycle (~10%)1. Mitosis – Division of nucleus (karyokinesis)2. Cytokinesis – Division of cell

B. Interphase• Growth and replication of chromosomes1. G1 (Gap) Phase – Growth phase (longest, most variable)2. S Phase – DNA synthesis (chromosome replication)3. G2 (Gap) Phase – Growth phase (synthesis of proteins,

other molecules)

Fig. 12.6

Fig. 12.6

IV. Mitosis

• Unique to eukaryotes• Reliable: ~1 error per 100,000 cell divisions• Continuous process divided into five stages

• G2 of Interphase

1) Prophase

2) Prometaphase

3) Metaphase

4) Anaphase

5) Telophase• Cytokinesis

Fig. 12.7

Fig. 12.7

IV. Mitosis

A. Mitotic Spindle• Composed of microtubules (polymers of tubulin)

• Microtubules are polar:• growing (+) end • non-growing (–) end

• Moves centrosomes to opposite poles of cell• Tugs chromosomes through cytoplasm• Orients chromosomes along metaphase plate• Elongates cell during anaphase• Separates sister chromatids; pulls them to

opposite poles of cell• How do the MTs do all this?

Fig. 12.8

Fig. 12.9

Anaphase

IV. Mitosis

B. Cytokinesis• Cell division following telophase• Different in animal cells (no cell walls) vs.

plant cells (cell walls)

Fig. 12.10

(Actin)

Fig. 12.11

Mitosis in Plant Cells

IV. Mitosis

C. Binary Fission• Occurs in bacteria• Does not involve mitosis

• No mitotic spindle• Single circular chromosome

Fig. 12.12

IV. Mitosis

D. Evolution of Mitosis• Presumably, binary fission arose before mitosis• Some proteins involved in binary fission are

related to eukaryotic proteins (tubulin, actin)

Fig. 12.13