Mitosis & Meiosis

1. Mitosis & Meiosis

2. Cell Division • like begets like (more or less) • reproduction occurs at the cellular level • have to give genetic material to new cell • asexual • sexual • haploid = one set of DNA (1n) • diploid = 2 sets of DNA (2n)

3. Asexual • production of genetically identical offspring by a single parent • 1 parent cell (2n) → 2 daughter cells (2n) • DNA is identical • aka: cloning • whole organisms • cells within an organism (growth & repair)

4. Sexual • production of genetically unique offspring • genetic contribution from 2 different parents • need to reduce the amount of DNA by half • creates gametes (egg & sperm) • gamete + gamete → new organism • (1n) + (1n) → (2n)

5. Prokaryotes: Binary Fission • single chromosome • circular • small and uncomplicated • stimulus to divide: lots of food • get too large: own waste = death • need ATP to: • make new set of DNA • make new cell ‘stuff’

7. Figure 8.2B Prokaryotic chromosomes

8. Eukaryotes: Mitosis • larger, more complex cells • large numbers of chromosomes • chromosomes in pairs: 1 from mom & 1 from dad • DNA is unwound most of the time: chromatin • duplicate in this form = 4 sets of DNA • time to divide, need to organize: wind up into chromatids

9. Eukaryotes: Mitosis • cells spend most of their time in Interphase • G1 phase: doing it’s thing but able to start dividing • G0 phase: doing it’s thing but can’t divide • S phase: synthesis (duplicate DNA & centrosome) • G2 phase: really getting ready to divide http://aprenderasbiologia.blogspot.com/2011/01/ciclo-celular.html

11. http://scienceblogs.com/transcript/2006/08/new_evidence_for_endosymbiotic.phphttp://scienceblogs.com/transcript/2006/08/new_evidence_for_endosymbiotic.php

14. http://www.youtube.com/watch?v=PvDlilBgoSs http://www.biologyjunction.com/cell_division_notes.htm http://usmle-review.org/cell-cycle.php

15. Eukaryotes: Mitosis • Prophase • chromatin condenses into sister chromatids • mitotic spindle forms • microtubules attach to the centrosomes & centromere • nuclear membrane breaks down • mitotic spindle starts pushing chromatids toward middle of ce

17. Eukaryotes: Mitosis • Metaphase • all the centromeres are lined up at equatorial plane • Anaphase • checkpoint • ATP used to push and pull centromeres toward poles • poles pushed away from each other too • fastest phase

19. Eukaryotes: Mitosis • Telophase • ‘reverse’ of prophase • chromatids unwind • spindle breaks down • nucleus reforms • Cytokinesis • contractile ring of actin & myosin forms (hoodie) • plants form a cell plate → cell wall • make more ‘stuff’

22. Figure 8.6A Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Cleavage furrow

24. Mitosis: Summary • start with 1 2n parent • end up with 2 2n daughter cells • DNA in daughter cells is IDENTICAL • to each other • to parent cell

26. Meiosis • start with 1 2n parent cell • produce 4 1n gametes • DNA is UNIQUE • each gamete is different than the others • each gamete is different than the parent

27. Meiosis • somatic cells (body cells) • have 2 sets of chromosomes • called homologous pairs • code for same things, (like eye color) but may have different information (blue or brown) • 22 pairs of austosomes • 1 pair of sex chromosome (XX in female; XY male)

28. Meiosis • gametes (1n) • have 1 set of chromosomes • meant to pair up with another gamete (1n) to create a 2n organism • gamete + gamete → zygote (fertilization) (1n) + (1n) (2n) gametes created through process of MEIOSIS

29. Meiosis • DNA is copied ONCE • cells divide TWICE • cross-over: homologous chromosomes swap material = increased genetic diversity

30. Mom Dad http://medakagb.lab.nig.ac.jp/Homo_sapiens/index.html

31. Mom Dad http://medakagb.lab.nig.ac.jp/Homo_sapiens/index.html

32. http://ghr.nlm.nih.gov/handbook/illustrations/normalkaryotypehttp://ghr.nlm.nih.gov/handbook/illustrations/normalkaryotype

34. Figure 8.12B INTERPHASE MEIOSIS I MEIOSIS II Sister chromatids 2 1 3 A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes

35. Figure 8.11 Pair of homologous chromosomes Locus Centromere Sister chromatids One duplicated chromosome

36. http://click4biology.info/c4b/4/gene4.2.htm

37. Meiosis • Interphase: • chromosomes duplicated • centrosomes duplicated

39. Meiosis • Prophase I: • chromatin coils up • synapsis: 2 sister chromatids come together (tetrad) • cross over occurs • can take months • centrosomes go to poles • spindle foms • nuclear envelope breaks down

41. Meiosis • Metaphase I: • tetrads are aligned across from each other at equator • sister chromatids across from each other • not all centromeres along equator

43. Meiosis • Anaphase I: • sister chromatids pulled away from each other • uses ATP to push/pull chromatids toward poles • uses ATP to push poles away from each other

45. Meiosis • Telophase I and Cytokinesis: • nuclear membrane reforms • chromatids uncoil into chromatin • some species skip this • short interphase (rest)

47. Meiosis • Prophase II: • centosomes duplicate • spindle forms • chromosomes moved toward equator • Metaphase II: • centromeres aligned on equator

49. Meiosis • Anaphase II: • centromeres of sister chromatids pulled apart • ATP used to push/pull chromatids toward poles • ATP used to push poles away from each other • Telophase II & Cytokinesis: • nuclei reform • DNA uncoils