+ Meiosis Sexual Reproduction

True or False ● The role of mitosis is the production of new somatic cells. ● Any cell with two copies of each kind of chromosome is called haploid. ● The part of mitosis where sister chromatids line up on the equatorial line is known as anaphase. ● If a sperm cell contains 8 chromosomes, it comes from an animal that has 16 chromosomes. ● During cytokinesis cells will divide into two equal daughter cells.

+ Where do you come from?

+ Sex: Woman, XX Man, XY Gender: Female Male Egg, OvumSperm According to the World Health Organization, "Sex refers to the biological and physiological characteristics that define men and women. Gender refers to the socially constructed roles, behaviors, activities, and attributes that a given society considers appropriate for men and women

+ Fertilization – union of sperm an egg to produce zygote

+ Fertilization Sperm and egg cells – gametes

+ Fetus Development Fertilization Mitosis to Create More CellsFetus

+ 23 pairs of chromosomes 1 from mom,1 from dad 46 individual chromosomes Body cells have all these chromosomes – diploid (2n) Gametes have ½ the amount because they will combine to eventually form body cells– haploid (n) (hap  half)

23 46 n n 2n Homo sapiens – 46 chromosomes, 23 pairs

+ Diploid and Haploid Practice

+ Got it? Questions 1. In humans, the cardiac muscle cells, skin cells, and neurons, of humans all have ____________ chromosomes 2. The sperm and egg cells are called ______________ 3. In humans an ovum (egg cell) would have _____ chromosomes 4. When a cell like a gamete has ½ the amount of chromosomes it is called ___________and symbolized as n 5. When a body cell like a skin cell has the full amount of chromosomes it is called __________, and symbolized as 2n 6. If a sperm cell has 8 chromosomes it came from a male with _____ chromosomes. 46 gametes 23 haploid diploid 16

+ Meiosis (My-oh-sis) Definition: Process by which 1 diploid eukaryotic cell divides twice to generate 4 haploid gametes Gametes – sperm or cells Produces 4 cells each with 1 copy of each chromosome Purpose: When the egg is fertilized by a sperm the new zygote has the same number of chromosomes as the parents Zygote has 2 of each chromosomes (1 from mom, 1 from dad) Allows multicellular organisms to reproduce sexually Animation:

+ Special cells that divide in meiosis to become sperm and egg Start off diploid (2n)

+ Interphase 1 – Oocyte or Spermatocyte Replication - S

+ Prophase 1 and Prophase 2

+ Metaphase 1 and Metaphase 2

Meiosis Phases – watch the chromosomes move ● Centromeres divide the chromosome short arm and long arm. ● Chromatids or sister chromatids (two identical copies of DNA) are connected by the centromere ● Telomeres protect DNA, during DNA replication.

+

+ =rB_8dTuh73c

+ Purpose Continued Provides great genetic diversity Offspring have the same # of chromosomes as parents Some of those chromosomes came from each parent Offspring typically have characteristics from both parents

+ Prophase I Nuclear envelope breaks down DNA condenses into chromosomes Each chromosome has 2 sister chromatids Homologous Chromosomes Pair Different from Mitosis Crossing over occurs, which creates Genetic diversity!!!

+ Crossing Over Sections of DNA from the chromosome of one parent are switched with the same section from the other parents DNA Allows one chromosome to contain alleles from both parents Occurs homologous chromosomes line up at equator Increases genetic diversity

+ Metaphase I Homologous Chromosomes line up along equator of the cell 2 Homologous Chromosomes = 4 Sister Chromatids Which side each homolog lines up on is random chance a daughter cell will get a chromosome from mother or father

+ Anaphase I Homologous Chromosomes are separated Each with 2 Sister Chromatids 1 of each homologous chromosome moves to opposite ends of the cell Results in 1 of each chromosome (2 sister chromatids) at each end

+ Telophase I (Final Phase) Nuclear envelope may reform 2 haploid nuclei are produced Each has 1 of each chromosome

+ Cytokinesis Not part of Meiosis I Occurs as Meiosis I is ending Cell divides

+ Result of Meiosis I and Cytokinesis 2 genetically different cells (Remember Crossing Over) Each cell contains 1 copy of each chromosomes 2 Sister Chromatids each

+ Prophase II Nuclear envelope breaks down DNA condenses into chromosomes Each chromosome has 2 sister chromatids

+ Metaphase II Sister Chromatids line up along equator of the cell 1 of each Chromosome 2 Sister Chromatids Different than Mitosis and Meiosis I

+ Anaphase II Sister Chromatids are separated 1 of each chromosome moves to opposite ends of the cell Results in 1 of each chromosome (no sister chromatids) at each end

+ Telophase II (Final Phase) Chromosomes unwind Nuclear envelope reforms in each new cell 4 haploid nuclei are produced Each has 1 of each chromosome

+ Cytokinesis Not part of Meiosis II Occurs at the end of Meiosis II Cells divide

+ Result of Meiosis II and Cytokinesis 4 genetically different haploid cells All contain some chromosomes from mother and some from father Each contains 1 of each chromosomes No Sister Chromatids

+ Comparing mitosis vs. meiosis Animation: _view0/chapter2/animation__comparison_of_meiosis_and_ mitosis__quiz_1_.html _view0/chapter2/animation__comparison_of_meiosis_and_ mitosis__quiz_1_.html