Reduction-Division Genetic Recombination 1

 Mitosis replicates an EXACT COPY of a cell with a complete set of 46 chromosomes!!! (23 pairs)  Mitosis starts with ONE parents cell and divides to create 2 IDENTICAL daughter cells  One DIPLOID cell creates 2 DIPLOID cells 2

 In Meiosis, we will be taking ONE parent cell and creating 4 daughter cells, each with different DNA!  This is SEXUAL REPRODUCTION  One DIPLOID cell creates 4 HAPLOID cells 3

 Diploid cell- Cell that has 46 chromosomes  Haploid cell – Cell that has 23 chromosomes  Diploid – 2n  Haploid- n 4

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). 5

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 6

2n=46 human sex cell diploid (2n) n=23 Meiosis I n=23 sperm haploid (n) Meiosis II 7

2n=46 human sex cell diploid (2n) n=23 Meiosis I n=23 egg Haploid (1n) Meiosis II 8 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. 9

visible  Nucleus and nucleolus visible. Nucleus nucleolus cell membrane chromatin 10

 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 11 Prophase I

 Longest and most complex phase (90%).  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). 12

“1 set” of chromosomes (2 X’s) Chromosomes that carry genes to code for a specific trait 2 chromosomes carry same gene to code for trait (hair color, eye color….etc..)? They are homologous chromosomes! 13

14 Homologs contain DNA that codes for the same genes, but different versions of those genes Genes occur at the same LOCATION on the chromosome

Homologous chromosomes sister chromatids Tetrad 15

chromosomessimilar in shape and size.  Pair of chromosomes 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 16

PaternalMaternal eye color locus eye color locus hair color locus hair color locus 17

 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 18

 Crossing over is why all egg and sperm have slightly different genetic code!!  This is why you DO NOT look identical to your older/younger brother or sister! 19

nonsister chromatids chiasmata: site of crossing over variation Tetrad 20

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XX chromosome - female XY chromosome - male 22

Homologs separate 23 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 24 TETRAD

 Shortest phase  Homologou chromosomes align on the equator. 25

Homologous chromosomes line up at equator OR 26

 Formula: 2 n  Example:2n = 4 then 1n = 2 then 1n = 2 thus2 2 = 4 combinations thus2 2 = 4 combinations 27

 Homologous chromosomes  Homologous chromosomes separate and move towards the poles.  Sister chromatids centromeres  Sister chromatids remain attached at their centromeres. 28

29 Homologs separate Homologs separate

haploid chromosomes  Each pole now has haploid (1n) set of chromosomes.  Cytokinesis  Cytokinesis occurs and two haploid daughter cells are formed. 30

31 cytokinesis

Sister Chromatids Separate 32 Meiosis II

 No Interphase II or very short  No DNA Replication  Remember: Meiosis II is SAM AS mitosis 33

 Same as Prophase in mitosis  Nucleus & nucleolus disappear  Chromosomes condense  Spindle forms 34

 Same as Metaphase in mitosis Chromosomes (not homologs) line up at equator 35

Anaphasemitosis  Same as Anaphase in mitosis  SISTER CHROMATIDS separate 36

 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) 37 1n Sperm cell fertilizes 1n egg to form 2n zygote

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 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 39

 What are the 2 sources of genetic recombination or variation? 40

1. CROSSING OVER (prophase I) 2. RANDOM FERTILIZATION 41

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? 42

 10 chromosomes (haploid or 1n) 43

 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 44 Male - XY

45 Female - XX

46 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 47

40 chromatids chromosomes  A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes? 48

 10 chromosomes 49