1. Evolution of eukaryotic genomes (Gene 342)
Lecture 1

3. Lecture outline Regulation of genome replication Cell division
cell cycle
Cell division
mitosis
Meiosis

4. Regulation of eukaryote replication – cell cycle
Series of events which coordinate replication in eukaryote cells
consists of four phases
G1 phase
S phase Interphase
G2 phase
M phase - Mitotic phase

5. G1 phase Period before mitosis, cytokinesis and the S-phase
Major phase for cell growth
New organelles synthesized – great amount of protein synthesis
Metabolic rate of the cell is high

6. S phase Synthesis phase – DNA replication and synthesis occur
chromatids  sister chromatids
Genetic material duplicated
individual chromosomes cannot be seen (chromatin)

7. G2 phase Shortest part of interphase (4-5 hrs) Nucleus well-defined
At least one nucleolus present
Prepares the cell for mitosis

8. Go Cells metabolically alive but out of cell cycle
Therefore, do not divide
Irreparable cells eg. Brain, eye and heart muscle cells

9. M phase (mitosis) Chromosomes condense and become visible
Chromosomes organised by microtubules
Microtubules assemble in a complex array (spindle)

10. Cell Division - Mitosis
growth and repair
result is genetically identical cells

11. Cell division – Meiosis I
Definitions
Diploid - having two complete sets of chromosomes (2n)
Haploid – having a single set of chromosomes (n)
Homologous chromosomes – members of a chromosome pair, one from each parent
Heterologous chromosomes – chromosomes from different pairs
Gamete – haploid reproductive cells
Zygote – fertilized egg cell

12. Meiosis II - progression
Chromosome duplication
Meiotic division I
Meiotic division II
Result is four, genetically different, haploid cells
Diploid meiocyte 2n 4n
Division I 2n
Division II n
Nonidentical haploid cells

13. Meiosis – Prophase I divided into 5 stages
Leptonema – duplicated chromosomes condense and homologues associate
Zygonema – synapsis and formation of the synaptonemal complex
Pachytene – crossing over occurs
Diplontene – chiasmata visible
Diakenesis – chromosomes move to central plane perpendicular to axis of spindle

14. Meiosis I Metaphase I Anaphase I Telophase I
paired chromosomes orient towards opposite poles
Anaphase I
chromosome disjunction (separation of bivalents)
Telophase I
Spindle dissembled
Daughter cells separated by membrane
Chromosomes condense and nucleus forms

15. Meiosis II Prophase II Metaphase II Anaphase II Telophase II
Chromosomes condense and attach to new spindle
Metaphase II
Chromosomes move to equatorial plane
Anaphase II
Centromeres split and chromatids move to opposite poles
Telophase II
New nuclei form around chromatids in daughter cells

16. Meiosis III - recombination
Prophase I (Pachytene)
crossing over occurs
exchange of genetic material between homologous pairs
Anaphase I
separation of maternally and paternally inherited chromosomes into different daughter cells

17. Meiosis Haploid products develop into gametes Females Males
¼ becomes an egg cell (oogenesis)
others become polar bodies
Males
All four become sperm cells (spermatogenesis)