DNA Terminology…. The Cell Cycle…. Mitosis and Meiosis…..

I. Chromosomes A. DNA wrapped around proteins (histones) is a nucleosome B. Uncoiled, threadlike DNA is Chromatin (non-dividing cell) (non-dividing cell) C. DNA called a chromosome chromosome in dividing cells; in dividing cells; short, fat rods short, fat rods

D.Half of a doubled Chromosome = a Chromatid 1.Contains two identical parts 2. Attach at a point called the Centromere E. Homologous Chromosomes 1.Occurs in pairs; same size and shape 2.Structurally different from all other pairs all other pairs 3. Have the same gene locations centromerechromatid

F. Gene F. Gene 1. Distinct unit on a chromosomes 2. Sequence of nucleotides Eye Color

II. “N” Number = The number of chromosomes a cell has A.Diploid (2N) 1.Each species has a characteristic number of chromosomes 2.Cells with both chromosomes of every pair called somatic or body cells a)2N for humans = 46 b)Ex: Crayfish (200) fruit flies (4) fruit flies (4) Common Name Genus and Species Diploid Number Buffalo Bison bison 60 Cat Felis catus 38 Cattle Bos taurus, B. indicus 60 Dog Canis familiaris 78 Donkey E. asinus 62 Goat Capra hircus 60 Horse Equus caballus 64 Human Homo sapiens 46 Pig Sus scrofa 38 Sheep Ovis aries 54

B.Haploid (1N) 1.Cell with 1 chromosome of each pair 2.Sex cell (sperm or egg)-Gametes

III. Asexual and Sexual Reproduction A. Mitosis is Asexual 1. Functions include a)Unicellular Organism = Reproduction b) Multi-cellular Organisms 1)Growth and development from egg 2)Replacement of dead or damaged cells c) Passes along the genome (total DNA per species) 2. Each daughter cell is clone of parent.

B. Meiosis is Sexual 1.Mixes DNA 2.Produces ½ the number of the chromosomes of the parents 3.Cells involved in sexual reproduction are sperm and are sperm and eggs (gametes) eggs (gametes)

IV. Cell Division A.Prokaryotes: Called Binary Fission B.Eukaryotes: Use the Cell Cycle 1.Interphase 2.Mitosis 3.Cytokinesis

V. Cell Cycle  = sequence of growth and division in the life of a cell

G 1 (growth;Gap 1) S= Synthesis G 2=Gap 2 1 hr. Cytokinesis Mitosis Rapid cell growth Cell doubles in size Enzymes + organelles double in number Growth DNA makes a copy of itself 11 hrs. 7 hrs. Rapid Growth Final preparation for cell division 3 hrs. Interphase

Cell Cycle = Interphase = period of cell growth and duplication of the DNA G 1 + S + G 2 Mitosis = division of the cell’s nucleus in which the chromosomes in the parent cell divides into 2 identical sets Cytokinesis = cytoplasm divides in 2 daughter cells

VI. Stages of Mitosis Prophase a) Early Prophase 1)Chromatin coils to chromosomes 2)Nucleolus & nuclear membrane break down & disappear 3)Centrioles move to poles (animal cells only).

b)Middle Prophase 1)Spindle fibers (microtubules) appear 2)Polar – centriole to centriole 3)Kinetochore – centromere to centriole

c)Late Prophase 1)Aster appear (centriole and fibers) (centriole and fibers) 2) Chromosomes position is random position is random

Metaphase a)Kinetochore fibers move chromosomes b)Chromosomes line up along equator

Anaphase a)Centromere splits b)Sister chromatids pulled to opposite ends

Telophase a)Identical chromatids at opposite end b)Chromatids unwind & elongate to chromatin c)Centrioles & spindle disappear d)Nucleolus & nuclear membrane reappear

1.Prophase 2.Metaphase 3.Anaphase 4.Telophase

C.Cytokinesis 1.Animal cells form cleavage furrows 2.Plant cells form a cell plate

VII. Reproduction and Meiosis A.Meiosis in males ♂ 1. Part of spermatogenesis 2. Occurs in the testes 3. Always results in four sperm cells

B.Meiosis in females ♀ 1.Part of oogenesis 2.Occurs in the ovaries 3.One cell receives most of the cytoplasm; the other 3 cells are polar bodies 4.Results in mature egg ( with 23 chromosomes) ( with 23 chromosomes)

VIII. Significance of Meiosis A.Produces genetic variation B.Without meiosis, chromosome numbers would continually increase ( teenage mutant Ninja turtles) Common Name Genus and Species Diploid Number Buffalo Bison bison 60 Cat Felis catus 38 Cattle Bos taurus, B. indicus 60 Dog Canis familiaris 78 Donkey E. asinus 62 Goat Capra hircus 60 Horse Equus caballus 64 Human Homo sapiens 46 Pig Sus scrofa 38 Sheep Ovis aries 54

IX. Review “N” Number Mitosis => results in 2N Meiosis => results in 1N animals (1N)plants (1N) egg and sperm spores and seeds (gametes)fuse (2N zygote) (2N zygote) * ♂ - sperm all viable after spermatogenesis * ♀ - after oogenesis, 1 egg(ootid) and 3 polar bodies (no cytoplasm, just DNA)

X. Steps of Meiosis (2 Separate Divisions)

Meiosis vs Mitosis

Meiosis I (starts with 2N) Prophase I  Chromatin shortens and coils to chromosomes  Spindle appears  Nucleolus and nuclear membrane disappear  Unique step: –Chromosomes line up next to their homologs (called synapsis) –Homolog pairs twist tightly to form a tetrad –(4 chromatids that make up two doubled chromosomes) –Crossing over can occur; exchange of DNA between homologs and/or 2 sister chromatids

Tetrad Formation

Meiosis I Metaphase I  Tetrads move to the equator; homolog pairs stay together Anaphase I  Homologous pairs separate and move to each pole ( one chromosome of each pair pulled to pole)  2 chromatids still joined at centromere

Meiosis I Telophase I  Cytoplasm divides forming 2 daughter cells

Meiosis II (chromosomes do not double; ends with 4 (1n) cells Prophase II  New spindle forms  Nuclear membrane and nucleolus break apart  Chromatin shortens and becomes visible as sister chromatids Metaphase II  Sister chromatids move to the equator

Meiosis II Anapahse II  Centromere divides; sister chromatids move to opposite poles Telophase II  Nuclear membrane reforms; Spindle disappears  Cytokinesis occurs  4 daughter cells from one parent