Homework: 11-4 worksheets

Daughter cells are clones of each other And of the original parent

Interphase Somatic cells: Mitosis Germ cells: Meiosis

Daughter cells are unique to each other And have half the DNA of the original parent

In humans, one set of chromosomes consists of 23 chromosomes. The haploid number (n) equals 23.

 Photograph of chromosomes grouped in order of pairs

Interphase Just like before Mitosis, Interphase includes Growth, Protein Synthesis and DNA Replication.

M e i o s i s I Interphase M e i o s i s I I

Tetrads line up in the middle Spindle fibers connect to centromere of chromosomes Homologous chromosomes separate Spindle fibers shorten Homologous chromosomes are forming new nuclei Cytokinesis forms 2 Haploid cells M e i o s i s I Prophase ITelophase IAnaphase IMetaphase I

Nuclear envelope breaks down Spindle fibers form Chromosomes line up in the middle Spindle fibers connect to centromere of chromosomes Sister Chromatids separate Spindle fibers shorten Chromosomes are forming new nuclei Cytokinesis forms 4 Haploid cells Prophase IITelophase IIAnaphase IIMetaphase II M e i o s i s I I

Meiosis Overview:  Start: Diploid germ cell with homologous chromosomes (2n=46)  Replicate DNA: still diploid, now 2 identical copies of DNA  Meiosis I: homologous chromosomes separate, now haploid (n=23), sister chromatids attached  Meiosis II: haploid (n=23), sister chromatids separate

2 nd Meiotic division (haploid) 1 st Meiotic division (haploid) After DNA Replication (diploid) (diploid male germ cell) Finished Sperm cells (haploid)

2 nd Meiotic Division (haploid) After DNA Replication (diploid) (diploid female germ cell) 1 st Meiotic Division (haploid) first polar body (haploid) three polar bodies (haploid)

 Independent assortment › Each gamete you produce contains one of roughly 8 million possible combinations of chromosomes inherited from your mother and father.  Random fertilization › The random fusion of a single sperm with a single ovum during fertilization will produce a zygote with any of about 64 trillion (8 million × 8 million) combinations of chromosomes! Factor these in with Crossing Over

123 Independent assortment: Chromosomes line up during metaphase I independently of each other. …the resulting gametes have a different assortment of chromosomes Two types of gametes

MitosisMeiosis What is produced?More CellsNew Organism Cell SimilarityIdentical CellsSimilar Cells Cell TypeSomatic ‘body’ Cells Gametes- sex cells Egg, Sperm # of Divisions1 Division2 Divisions Diploid/Haploid Cells 2 Diploid Cells4 Haploid Cells Chromosome #46 chromosomes/cell 23 Chromosomes/cell N ?2N- 2 copiesN- 1 copy

 In Mitosis  Cell division makes two clones of the parent cell  For growth, healing and asexual reproduction  Maintains the same number of chromosomes  In Meiosis  Cell division makes four unique daughter cells  With half of the DNA of the parent cell  To make sperm cells and egg cells (gametes)  Reduces the number of chromosomes by half

 Spindles do not attach properly during metaphase, and chromosomes or chromatids do not separate.  Results in too many or not enough chromosomes in gametes

Klinefelter’s Syndrome: XXY Turner’s Syndrome: X Down’s Syndrome: Trisomy 21

 Deletion When part of the chromosome breaks off  Duplication When part of the chromosome repeats itself  Inversion When two parts of a chromosome flip  Translocation when one part of a chromosome breaks off, then reattaches in the wrong place

Cri du Chat Syndrome: Deletion from Chromosome 5 Emanuel Syndrome: Translocation of 11 and 22 Chromosome 15q Duplication Syndrome: Diagnosed with Autism

 Meiosis occurs to form gametes for sexual reproduction  It involves forming 4 haploid daughter cells  Because of Crossing over, Independent Assortment and Random Fertilization, it increases genetic variability  Nondisjunction can result in the incorrect number of chromosomes.

 Somatic cells  Gametes  Haploid (n)  Diploid (2n)  Homologous chromosomes  Tetrad  Crossing over