Mitosis Meiosis Cell Division like begets like more

Mitosis & Meiosis

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

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

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 • (1 n) + (1 n) → (2 n)

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’

Figure 8. 2 B Prokaryotic chromosomes

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

Eukaryotes: Mitosis • cells spend most of their time in Interphase – G 1 phase: doing it’s thing but able to start dividing • G 0 phase: doing it’s thing but can’t divide – S phase: synthesis (duplicate DNA & centrosome) – G 2 phase: really getting ready to divide http: //aprenderasbiologia. blogspot. com/2011/01/ciclo-celular. html

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

http: //www. youtube. com/watch? v=Pv. Dlil. Bgo. Ss http: //usmle-review. org/cell-cycle. php http: //www. biologyjunction. com/cell_division_notes. htm

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

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

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’

Figure 8. 6 A Cytokinesis Cleavage furrow Contracting ring of microfilaments Daughter cells Cleavage furrow

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

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

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)

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

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

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

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

Figure 8. 12 B MEIOSIS I INTERPHASE MEIOSIS II Sister chromatids 2 1 A pair of homologous chromosomes in a diploid parent cell A pair of duplicated homologous chromosomes 3

Figure 8. 11 Pair of homologous chromosomes Locus Centromere Sister chromatids One duplicated chromosome

http: //click 4 biology. info/c 4 b/4/gene 4. 2. htm

Meiosis • Interphase: – chromosomes duplicated – centrosomes duplicated

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

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

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

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

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

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

Figure 8. 14 MEIOSIS I MITOSIS Parent cell (before chromosome duplication) Prophase Duplicated chromosome (two sister chromatids) Chromosome duplication Site of crossing over Prophase I Tetrad formed by synapsis of homologous chromosomes Chromosome duplication 2 n 4 Metaphase I Metaphase Chromosomes align at the metaphase plate Anaphase Telophase Tetrads (homologous pairs) align at the metaphase plate Anaphase I Telophase I Homologous chromosomes separate during anaphase I; sister chromatids remain together Sister chromatids separate during anaphase Daughter cells of meiosis I Haploid n 2 MEIOSIS II 2 n 2 n Daughter cells of mitosis No further chromosomal duplication; sister chromatids separate during anaphase II n n Daughter cells of meiosis II