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

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

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

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

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

Homologous chromosomes

Animations Mitosis animation mitosis.htm Meiosis animation meiosis.htm

Meiosis in plants comparison

 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

chiasma

 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)

 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)

 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…?

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

 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

 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.

 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

Make a Venn Diagram 30 MitosisMeiosis Both

 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

 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

 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.

Concept