 Turn in DNA projects  Vocab #14 instead of 18 (please correct it)  Quiz  Meiosis Notes  Compare and contrast Mitosis and Meiosis  HF: Check for understanding (3 questions) on last Friday and compare an contrast mitosis and meiosis today WELCOME 2/1-2/16 IT’S FEB! 4 MORE MONTHS!

PROCESS OF MEIOSIS

 What is a chromosome?  A piece of coiled DNA  How many chromosomes do human cells have?  46 (in non-sex cells)  Do ALL humans have the same number of chromosomes in their cells?  YES! (Except people with genetic disorders causing extra chromosomes or missing chromosomes)  Where did the 46 chromosomes come from? CHROMOSOMES

 If we get our chromosomes from our parent, why do we not have a total of 92 (46 from mom and 46 from dad)?  How does each parent manage to only give 23 chromosomes to their child? TURN TO A FRIEND AND DISCUSS…

 How are gametes (sex cells) formed, if they only have 23 chromosomes?  Through a process called MEIOSIS  Meiosis is similar to Mitosis but has some differences. SEX CELLS -- GAMETES

 Four Phases :  Interphase  Prophase  Metaphase (and)  Telophase  DNA replication happens before mitosis during the synthesis phase of the cell cycle. MITOSIS — QUICK REVIEW

 Meiosis Animation #1 Meiosis Animation #1  Meiosis Animation #2 Meiosis Animation #2 MEIOSIS

 Mitosis results in…  Two IDENTICAL daughter cells—no genetic diversity  Meiosis results in…  FOUR daughter cells—that are different from parent cells, resulting in genetic diversity MITOSIS VS. MEIOSIS—PRIMARY DIFFERENCE

Asexual ReproductionSexual Reproduction Uses only mitosis Produces clones—genetically identical offspring Fast and effective reproduction to spread organism No diversity Combination of two haploid sex cells Fertilization: combines genetic information from two separate cells with ½ of the original genetic information of parent organism Gametes are from separate parents. (female = egg, male = sperm) Zygote (new individual) has two sets of chromosomes, one from each parent Process changes diploid cells to haploid gametes—leading to an increase in diversity of offspring ASEXUAL VS. SEXUAL REPRODUCTION

 What is the advantage of an organism that reproduces sexually rather than asexually?  An organism that reproduces sexually will have more genetic diversity than one that reproduces asexually. ASEXUAL VS. SEXUAL REPRODUCTION

 Four Phases:  Prophase I  Metaphase I  Anaphase I (and)  Telophase I  Genetic diversity results from meiosis I. MEIOSIS I

 Homologous (same) chromosomes pair (synapsis)  Homologous pairs called bivalents—two chromosome with four chromatids  Nuclear membrane dissolves  Chromosomes attach to spindle fibers and begin to move PROPHASE I

 Homologous chromosomes (bivalents) line up at the equator to form tetrads.  Random orientation results in diversity.  50/50 chance of getting either parent’s homologue for each chromosome METAPHASE I Tetrad

 Homologous chromosomes separate.  Chromosomes with TWO chromatids move to opposite poles.  Daughter cells will have 23 chromosomes (haploid) but with two chromatids. ANAPHASE I

 Nuclear membrane begins to reform  Cell may quickly move to meoisis II TELOPHASE I

 Similar to mitosis BUT no synthesis phase (no DNA replication)  Chromatids are NOT identical because of crossing over (recombination).  Separates chromatids and produces two daughter cells with 23 chromosomes that have one chromatid each MEIOSIS II

 Crossing Over: Exchange of genetic information between homologous chromosomes that results in recombinant chromosomes and genetic diversity IMPORTANT CONCEPTS!!!

 Independent Assortment : Chromosomes randomly line up during metaphase I, and there are various ways that the homologous chromosomes may line up—again resulting in genetic diversity IMPORTANT CONCEPTS!!!

 Contrast mitosis and meiosis with the following questions create a T-Chart:  1. in what type of cell does division take place?  2. what is the purpose of division?  3. How many divisions are there?  4. How many daughter cells are produced?  5. How many chromosomes are in the daughter cells?  6. Are the daughter cells identical to or different than parent cell?  7. Does crossing over occur? If so during what stage?  8. During what stage do the sister chromatids separate? CHECK FOR UNDERSTANDING