WARM UP  LIST THE 8 PHASES/STAGES OF THE CELL CYCLE (INCLUDE MITOSIS)  LIST 3 DIFFERENCES THAT YOU THINK OCCUR BETWEEN MITOSIS & MEIOSIS ANNOUNCEMENTS:  FRI: QUIZ & ARTICLE  MON: CELL PROJECTS DUE 1

2

3

4 WHAT TYPE OF CELL IS THIS?

 itself over & over…

 Take paper and cut out each stage  Glue on notecard  Write each stage on a separate notecard 6

 Similar to “Go Fish”  One person may:  Grab a card from the deck  Grab a card from the discard pile or  Ask a player for a card  At the end of turn, discard one card  Winner – the first to get 4 cards in the correct order 7

KINDA LIKE MITOSIS, BUT BETTER! 8

cell division GAMETES, HALF CHROMOSOMES,  The form of cell division by which GAMETES, with HALF the number of CHROMOSOMES, are produced.  DIPLOID (2n)  HAPLOID (n)  MeiosisSEXUAL reproduction.  Meiosis is SEXUAL reproduction.  TWO divisionsMEIOSIS I MEIOSIS II  TWO divisions (MEIOSIS I and MEIOSIS II). 9

GAMETES(sperm or egg)  Sex cells divide to produce GAMETES (sperm or egg). HALF  Gametes have HALF the # of chromosomes. GONADS (testes or ovaries).  Occurs only in GONADS (testes or ovaries).  Male: SPERMATOGENESIS - sperm  Female: OOGENESIS - egg or ova 10

2n=46 human sex cell diploid (2n) n=23 Meiosis I n=23 sperm haploid (n) Meiosis II 11

2n=46 human sex cell diploid (2n) n=23 Meiosis I n=23 egg Haploid (1n) Meiosis II 12 Polar Bodies (die)

mitosis  Similar to mitosis interphase.  CHROMOSOMES (DNA) S phase  CHROMOSOMES (DNA) replicate in the S phase chromosometwo identical SISTER CHROMATIDS CENTROMERES  Each duplicated chromosome consist of two identical SISTER CHROMATIDS attached at their CENTROMERES.  CENTRIOLE  CENTRIOLE pairs also replicate. 13

visible  Nucleus and nucleolus visible. Nucleus nucleolus cell membrane chromatin 14

 Cell division chromosome number one- half.  Cell division that reduces the chromosome number by one- half.  Four phases  Four phases: a.Prophase I b.Metaphase I c.Anaphase I d.Telophase I 15 Prophase I

Nucleus & Nucleolus Nucleus & Nucleolus disappear Spindle Spindle forms coilSynapsis Chromosomes coil & Synapsis (pairing) occurs Tetrads Crossing over Tetrads form & Crossing over Occurs centrioles spindle fiber aster fibers 16 TETRAD

 Chromosomes  Chromosomes condense.  SynapsisHomologous chromosomes tetrad  Synapsis occurs - Homologous chromosomes come together to form a tetrad.  Tetrad two chromosomes four chromatids  Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids). 17

18 Homologs contain DNA that codes for the same genes, but different versions of those genes Genes occur at the same loci

Homologous chromosomes sister chromatids Tetrad 19

chromosomesmaternal paternalsimilar in shape and size.  Pair of chromosomes (maternal and paternal) that are similar in shape and size. (tetrads) carry GENES controlling the SAME inherited traits  Homologous pairs (tetrads) carry GENES controlling the SAME inherited traits. locus(position of a gene)  Each locus (position of a gene) is in the same position on homologues.  Humans23 pairs homologous chromosomes:  Humans have 23 pairs of homologous chromosomes: 22 pairs autosomes a.First 22 pairs of autosomes sex chrom osomes b.Last pair of sex chrom osomes 20 LOCI

PaternalMaternal eye color locus eye color locus hair color locus hair color locus 21

 Crossing over chromatids chiasmata  Crossing over may occur between non-sister chromatids at sites called chiasmata.  Crossing over chromatids chromatid  Crossing over: segments of nonsister chromatids break and reattach to the other chromatid.  Chiasmata (chiasma) exchange genes crossing over  Chiasmata (chiasma) are where chromosomes touch each other and exchange genes (crossing over.) Genetic Recombination  Causes Genetic Recombination 22

nonsister chromatids chiasmata: site of crossing over variation Tetrad 23

24

XX chromosome - female XY chromosome - male 25

Homologs separate 26 Meiosis I

Nucleus & Nucleolus Nucleus & Nucleolus disappear Spindle Spindle forms coilSynapsis Chromosomes coil & Synapsis (pairing) occurs Tetrads Crossing over Tetrads form & Crossing over Occurs centrioles spindle fiber aster fibers 27 TETRAD

Homologs line up at equator or metaphase plate OR 28

 Shortest phase  Tetrads align on the equator.  Independent assortment occurs – chromosomes separate randomly causing GENETIC RECOMBINATION 29

 Formula: 2 n  Example:2n = 4 then 1n = 2 then 1n = 2 thus2 2 = 4 combinations thus2 2 = 4 combinations 30

 In terms of Independent Assortment -how many different combinations of sperm could a human male produce? 31

 Formula: 2 n  Human chromosomes:2n = 46  n = 23  2 23 = ~8 million combinations 32

33 Homologs separate Homologs separate

 Homologous chromosomes  Homologous chromosomes separate and move towards the poles.  Sister chromatids centromeres  Sister chromatids remain attached at their centromeres. 34

35 cytokinesis

haploid chromosomes  Each pole now has haploid (1n) set of chromosomes.  Cytokinesis  Cytokinesis occurs and two haploid daughter cells are formed. 36

Sister Chromatids Separate 37 Meiosis II

 No Interphase II or very short  No DNA Replication  Remember: Meiosis II is similar to mitosis 38

 Same as Prophase in mitosis  Nucleus & nucleolus disappear  Chromosomes condense  Spindle forms 39

 Same as Metaphase in mitosis Chromosomes (not homologs) line up at equator 40

Anaphasemitosis  Same as Anaphase in mitosis  SISTER CHROMATIDS separate 41

42

 Same as Telophase in mitosis.  Nuclei and Nucleoli reform, spindle disappears  CYTOKINESIS occurs.  Remember: FOUR HAPLOID DAUGHTER cells are produced.  Called GAMETES (eggs and sperm) 43 1n Sperm cell fertilizes 1n egg to form 2n zygote

44

 Also known as GENETIC RECOMBINATION  Important to population as the raw material for NATURAL SELECTION.  All organisms are NOT alike  Strongest “ most fit” survive to reproduce & pass on traits 45

 What are the 3 sources of genetic recombination or variation? 46

1. CROSSING OVER (prophase I) 2. INDEPENDENT ASSORTMENT (metaphase I) 3. RANDOM FERTILIZATION 47

20 chromosomes (diploid) chromosomes  A cell containing 20 chromosomes (diploid) at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes? 48

 10 chromosomes (haploid or 1n) 49

 Aorganized picture arranged in pairs by size  An organized picture of the chromosomes of a human arranged in pairs by size from largest to smallest.  P1-22 AUTOSOMES  Pairs 1-22 called AUTOSOMES  LSEX CHROMOSOMES  Last pair are SEX CHROMOSOMES 50 Male - XY

51 Female - XX

52 Female - XX Down Syndrome – Trisomy 21

spermegg zygote  The fusion of a sperm and egg to form a zygote. FERTILIZED EGG  A zygote is a FERTILIZED EGG n=23 egg sperm n=23 2n=46 zygote 53

40 chromatids chromosomes  A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes? 54

 10 chromosomes 55

56

57