1. NO TEST TODAY!!! What is happening in metaphase? What is happening in anaphase? What is a chromosome? What is a chromatid? How and why do humans have 46 chromosomes? In other words, what must be true about the parents’ cells’ chromosomes

2. Meiosis and Sexual Reproduction Nine weeks exam  3/16 Mitosis and Meiosis Test on 3/18

3. Meiosis 2 divisions to make 4 genetically unique cells End result is 4 cells with half the number of chromosomes as parent cell Occurs only in sex organs First Division  meiosis I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis I

4. Second Division (Meiosis II ) Prophase II Metaphase II Anaphase II Telophase II Cytokenesis II

5. Meiosis I The cell’s chromosomes begin to pair up-called synapsis The pairs in meiosis I are called tetrads or “homologous pair of chromosomes” The goal of meiosis I is to break apart tetrads Meiosis II  Single Chromosomes separate and migrate to polls  Chromatids arrive at polls, turn into chromatin, and cell divides  The result is four cells with half the number of chromosomes as the parent cell

6. Homologous chromosomes

13. Animations Mitosis animation mitosis.htm Meiosis animation meiosis.htm

14. Meiosis in plants comparison

16.  When a gene or piece of DNA switches places with a gene or piece of DNA from a homologous chromosome  In other words, material from each parent can be switched between homologous chromosomes  If this occurs, genetic information can be exchanged  Prophase I of Meiosis I  Increases genetic diversity

17. chiasma

18.  Somatic Cells  “body cells”  non-sex cells  Germ cells  Name of the cell at the beginning of meiosis in reproductive organs  Gamete  sex cells (sperm and egg) at the end of meiosis  Autosomes  non sex chromosomes (the other 22 pairs)  Sex chromosomes- chromosomes which determine male and female X and Y (one pair)

19.  Haploid  a cell that has only one set of chromosomes  This means that the cell will have 23 chromosomes  Sex cells are haploid cells  A male haploid sperm cell and a female haploid egg cell will come together to make a diploid zygote (one celled embryo)

20.  Diploid  a cell or organism that has two sets of chromosomes  Diploid cells have 46 chromosomes  One from mom and one from dad  Two haploid cells come together and make a diploid organism  A diploid cell would be your somatic cells. Which are…?

21.  The process of creating sperm  Male meiosis  Every one meiosis cycle produces 4 sperm  Males do this constantly with little regulation

23.  Female meiosis  Process of making egg cells  Only one egg cell per meiosis cycle which lasts about 28 days  The other three cells are called polar bodies, In other words, three out of the four cells do not become eggs, they become polar bodies  Ovum  the mature egg once it has grown. It is ready to be fertilized by a sperm  Occurs inside the follicle of the ovary  Follicle

25.  Men produce millions of sperm, and each sperm has an equal chance of fertilizing the egg  Women produce multiple eggs per month, but only one is used for fertilization. The rest are used as polar bodies  Resulting is a randomly produced zygote with random alleles from each parent.

26.  Eggs are enclosed in a thin protective layer called the follicle  acts as a barrier to the sperm  Sperm have a tip called an acrosome  contains an enzyme called hyaluronidase  After the follicle has been penetrated, the sperm now reaches the Zona pallucida  thick coat protecting the cell membrane of the egg  Next, the acrosome breaks down the cell membrane  Finally, the sperm nucleus and the egg nucleus fuse together as one (zygote) ◦ During this process a glycoprotein is released by the sperm head in order to prevent the attachment of other sperm

30. Make a Venn Diagram 30 MitosisMeiosis Both

31.  Mixing of genetic information between chromosomes of the same organism or between two different organisms  Causes diversity in offspring  Can be done by man or natural  When done by man, called genetic engineering  when scientists transplant genetic material from one organism to another.  When natural  crossing over

32.  Alleles of different genes assort independently of one another during gamete formation  metaphase of meiosis I  the gamete can end up with any combination of paternal or maternal chromosomes  Increases genetic diversity  In humans there are 2 23 different combinations

34.  when any individual produces gametes, the alleles separate so that each gamete receives only one copy.  A gamete will receive one allele or the other.  In meiosis the moms and dads chromosomes get separated and the alleles with the traits of a character are segregated into two different gametes.

36. Concept