AGENDA Do Now! Meiosis Notes Meiosis (Amoeba sisters) Hands-on activity: Draw and Explain Meiosis Quizizz.com: Quick Assessment on your understanding Closure

Reminder!!! You have Test on Unit 4 on Friday 3/1/19

Do Now! 1. What are the 4 stages of Mitosis in order? 2. What results from Mitosis cell division? OR What is the END PRODUCT of Mitosis cell division? 3. What type of cells are divided in mitosis? 4. Write down all you remember from the discussion on Introduction to Meiosis.

Meiosis Vocab Review

Type of cells Somatic cells: also called body cells, make up most of your body tissues and organs. Gametes: sex cells—ova, or eggs, in the female, and spermatozoa, or sperm cells, in the male. DNA in your gametes can be passed on to your children.

Homologous Chromosomes two chromosomes—one inherited from the mother, one from the father—that have the same length, shape and size.

Autosomes and Sex chromosomes Chromosome pairs 1 through 22 make up your autosomes, chromosomes. Sex chromosomes 23rd pair chromosomes, directly control the development of sexual characteristics. Humans have 2 sex chromosomes, X and Y.

Diploid and Haploid Diploid (2n): means that a cell has two copies of each chromosome. Haploid(n): means that a cell has only one copy of each chromosome.

Sexual reproduction Sexual reproduction: involves the fusion of two gametes, resulting in offspring that are a genetic mixture of both parents.

Meiosis Meiosis is a form of nuclear division that divides a diploid cell into haploid cells. Occurs only in gonads (testes or ovaries) Males: 4 sperm are made Females: 1 ovum is made

Compare and Contrast

Description of Meiosis Similar to Mitosis 2 Divisions: Meiosis I Meiosis II End result – 4 genetically non- identical cells haploid (gametes) Men = 4 sperm Females = 1 egg

Spermatogenesis n=23 n=23 2n=46 human sex cell sperm haploid (n) meiosis II 2n=46 human sex cell diploid (2n) n=23 meiosis I

Fertilization n=23 egg 2n=46 zygote The fusion of a sperm and egg to form a zygote. A zygote is a fertilized egg. (diploid) n=23 egg sperm n=23 2n=46 zygote

Haploid (n): cell that has only one copy of each chromosome. Diploid (2n): cell that has two copies of each chromosome, one from an egg and one from a sperm

Homologous (same/structure) chromosomes One from father – paternal One from mother - maternal

Gametogenesis Gametogenesis is the production of gametes.

Crossing over during meiosis increases genetic diversity. Crossing over is the exchange of chromosome segments between homologous chromosomes during prophase I of meiosis I.

Phases of Meiosis

Interphase G1, S, & G2 take place as in mitosis Chromosomes are replicated during S phase (synthesis)

Prophase I DNA coils tightly. (Chromosomes condense) Synapsis occurs: two homologous chromosomes come together to form a tetrad. Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids). Homologous chromosomes pair up and crossing over may occur Crossing over: the exchange of chromosomal segments between a pair of homologous chromosomes. Nuclear membrane dissolves

Prophase I

Crossing over during meiosis increases genetic diversity. Crossing over is the exchange of chromosome segments between homologous chromosomes during prophase I of meiosis I.

Prophase I - Synapsis Homologous chromosomes sister chromatids Tetrad

Cross over in Meiosis

Crossing Over

Metaphase I Spindle fibers attach to the centromere of each chromosome Each tetrad lines up at the equator of the cell

Anaphase I Spindle fibers shorten and pull homologous chromosome pairs away from each other Each pole ends up with a complete haploid set of chromosomes

Telophase I Nuclear membrane reforms around daughter nuclei Each daughter nucleus has two sister chromatids for each chromosomes Because of crossing-over, the sister chromatids are NOT identical

Prophase II Nuclear membrane dissolves and new spindle fibers form

Metaphase II Spindle fibers bind to both sides of centromere Sister chromatids align at the equator of the cell

Anaphase II Spindle fibers shrink Sister chromatids are pulled apart to opposite ends of the cell

Telophase II & Cytokinesis Nuclear membrane reforms around sets of daughter chromosomes Cell undergoes cytokinesis End result is 4 haploid cells

Non disjunction When sister chromatids, or homologs fail to separate during cell division.

Non- Disjunction

Meiosis – mouse testes Parent cell 1st division 2nd division 4 gametes

Question: A cell containing 40 chromatids at the beginning of meiosis would, at its completion, produce cells containing how many chromosomes? Answer: ?

Differences in meiosis In males: 4 mature sperm Males begin to produce sperm after puberty, produced constantly until death; meiosis II occurs immediately after meiosis I Much smaller than egg (60 microns) May have X or Y chromosomes Have flagella to move In females: 1 mature egg, 3 polar bodies which break down Women born with all eggs they will have, meiosis I occurs before birth, meiosis II occurs once a month Much larger (100 microns) Have all X chromosomes Has no method of movement

Gamete production Females have XX for last pair of chromosomes (23 pair) Males have XY for last pair (23 pair) Since all eggs are X, father determines the sex of the child since the sperm may be X or Y

Mitosis vs. Meiosis Cell Division Cell Type # Daughter Cells # Chromosomes Haploid or Diploid MITOSIS MEIOSIS

Closure/Bell Ringer What type of cells are formed during meiosis?