Chromosomes and Cell Reproduction Chapter 6 & 7

I. Chromosomes Chromosome- made of 2 exact copies of DNA coiled around proteins (*this is after replication but before cell division) Chromatid- each copy of the DNA on a chromosome Centromere- place where the chromatids attach to make a chromosome Genes- Segments of DNA on a chromosome that code for a specific protein/trait

*Draw a chromosome and label chromatids, centromere and gene

II. Chromosome Number Each human somatic cell (body cell) has 2 copies of 23 different chromosomes for a total of 46 chromosomes We inherit 1 of each chromosome from mom and 1 from dad Homologous Chromosomes- similar in size, shape and genetic content

D. Diploid cells- contain 2 sets of chromosomes, all somatic cells are diploid (ex. Somatic cells in humans have a total of 46 chromosomes) E. Haploid Cells- contain only 1 set of chromosomes, only gametes can be haploid (ex. Gametes in humans have 23 chromosomes)

III. Karyotypes A picture of the chromosomes of an organism arranged by size Used to examine an individuals chromosomes: Karyotypes can determine only 2 things about the organism: Sex of individual Any abnormalities in the chromosomes (number or shape

C. Humans have 1 pair of sex chromosomes and 22 pairs of autosomal chromosomes (non sex chromosomes) D. Sex Chromosomes- XX= Female XY= Male (the sex chromosomes are the last pair of chromosomes shown in a karyotype)

Trisomy – when there is three of a certain chromosome instead of the normal 2

IV. Cell Cycle G1 Phase- period of cell growth S Phase- when DNA replication occurs G2 Phase- cell growth and preparation for mitosis Mitosis- division of the nucleus Cytokinesis- division of the cytoplasm

Cell Cycle Animations http://www.cellsalive.com/cell_cycle.htm http://iknow.net/cell_div_education.html

V. Mitosis The division of the nucleus in somatic cells Chromosomes have replicated prior to the start of mitosis Produces 2 identical daughter cells 4 phases

Prophase- chromatin coils into chromosomes Nuclear envelope dissolves Spindle fibers form

2. Metaphase (middle) Chromosomes line up in the middle of the cell Centrioles move to opposite poles Spindle fibers attach to chromosomes

3. Anaphase (apart) Spindle fibers shorten and pull chromatids toward opposite poles

4. Telophase (opposite of prophase) Nuclear envelope forms around chromatids Chromatids uncoil Cleavage is formed Spindle fibers dissolve

Cytoplasm is divided in half E. Cytokinesis Occurs after Mitosis Cytoplasm is divided in half Cell membrane encloses each cell **New cells are now in interphase and the cell cycle starts over.

Mitosis Animation http://iknow.net/cell_div_education.html http://www.loci.wisc.edu/outreach/bioclips/CDBio.html

VI. Meiosis Two divisions of the nucleus Results in the formation of 4 gametes (egg, sperm) Halves the number of chromosomes (in humans from 46 to 23)

Stages of Meiosis I 1.*Prophase I- crossing over occurs, (portions of one chromosome are broken and exchanged with portions of the other homologue)**results in genetic variability 2. Metaphase I- homologous chromosome pair up together at the equator 3. Anaphase I- centromeres do not divide 4. Telophase I and Cytokinesis

Meiosis II 1. Prophase II 2. Metaphase II 3. Anaphase II 4. Telophase II & Cytokinesis http://www.tokresource.org/tok_classes/biobiobio/biomenu/meiosis/ Interphase P 1 M 1 A 1 T1 & C P 2 M 2 A 2 T 2 Cytokinesis

Females- called oogenesis, forms 1 ovum and 3 polar bodies Males- called spermatogenesis, forms 4 sperm cells

http://www. biologyexams4u http://www.biologyexams4u.com/2013/06/difference-between-spermatogenesis-and.html

Meiosis Animations Meiosis Animation Meiosis Square Dance Video