1. The process in which ( ) are produced. 2. Males produce cells and females produce cells through meiosis

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1 Name: Aim 35: What is Meiosis? Date: I. What is Meiosis? What is Meiosis? Which organisms undergo Meiosis? Where does Meiosis occur? What does Meiosis produce? What is Meiosis also known as? 1. The process in which ( ) are produced. 2. Males produce cells and females produce cells through meiosis reproducing organisms (humans, animals etc). Egg and sperm cells must be created through meiosis before sexual reproduction can occur. 1. Sperm are produced in the of males (produced continuously throughout life) 2. Eggs are produced in the of females (all produced before the female is born) 1. Meiosis begins with with a set of chromosomes (diploid cell = 2 of every chromosome) Ex: In humans, meiosis begins with a body cell with 46 chromosomes (23 pairs) 2. Meiosis ends with with a set of chromosomes (haploid cell = 1 of every chromosomes) Ex: in humans, meiosis ends with a sperm or egg cell with 23 chromosomes (no pairs) = the formation of gametes (egg and sperm) through meiosis II. Chromosomes and Chromosome Number A) Chromosome Number To have a complete set of chromosomes. A cell that has 2 of each chromosome in a pair (1 form each parent) To have a half set of chromosomes. A cell that has 1 of each chromosome not in a pair. Body cells (liver cell, eye cell, heart cell, root cell of a plant etc.) Any cell BESIDES a reproductive cell Gametes (Egg and sperm.) ONLY reproductive cells. 1. The human diploid number is: 2. The human haploid/monoploid number is: 3. One chromosome of each chromosome pair is from the and one is from the 4. A human cheek cell has chromosomes because it is a cell. 5. A human egg cell has chromosomes because it is a cell.

2 6. The diploid number for an organism is 16. How many chromosomes are in a body cell of that organism?. How many chromosomes are in an egg or sperm cell of that organism?. So n = & 2n = 7. Complete the chart below # Chromosomes in body cells # Chromosomes in gametes # Chromosome pairs in body cells Horse 60 Fly 6 Spinach 12 Chicken 8 B) Homologous Chromosomes The chromosomes of a body cell (diploid cells) are in the form of. Therefore, in a human body cell there are of homologous chromosomes o Body cells have 23 chromosomes are from the mother and 23 chromosomes are from the father. o Egg and sperm cells have only one member of this homologous pair Homologous Pairs or Homologous Chromosomes are similar in size/shape, control the same and have genes for the same characteristic III. Phases of Meiosis: Meiosis involves 2 divisions: Meiosis I and Meiosis II divisions cells created Produces and Daughter cells are to parent cell BEGIN with ONE CELL END with 4 CELLS

3 Interphase *MEIOSIS I* (1st Division) Prophase I 1. Chromosomes replicate in one diploid body cell 2. Chromosomes cannot be seen This is the ONLY time during meiosis that the chromosomes replicate 3. Chromosomes from each parent pair up and form homologous pairs 4. Crossing over occurs (homologous chromosomes exchange genetic information, creating new gene combinations) Metaphase I 5. Chromosome pairs line up in the middle of the cell (Pairs have 1 chromosome from mom and 1 from dad) Anaphase I 6. Chromosome pairs are split apart and move to opposite ends of the cell. This is called disjunction Telophase I & Cytokinesis I 7. Cell tears and two daughter cells are created, each with duplicated chromosomes *MEIOSIS II* (2nd Division) Prophase II 8. The two cells each undergo the same process as mitosis except the chromosomes DO NOT replicate again Metaphase II Anaphase II Telophase II & Cytokinesis II 9. Chromatids separate 10. The cytoplasm of each cell tears and 4 haploid sex cells are produced, each with half the number of chromosomes as the original body cell 11. Each cell has 1 chromosome from each pair of homologous chromosomes. Chromosomes are NOT paired

4 IV. Meiotic Division How does Meiosis differ in Males and Females? MALES FEMALES = creation of sperm = creation of eggs Diagram What is produced viable sperm cells Cytoplasm divides in each division Produces large viable egg cell and small nonfunctioning cells called, which eventually disintegrate Why are gametes produced A haploid sperm and a haploid egg will combine during the process of to create a (single cell) that will eventually divide by and grow into an organism. V. Meiosis as a Source of Genetic Variation The events that occur during meiosis do more than just divide chromosomes into smaller sets and form smaller cells. Meiosis is responsible for much of the genetic variation among sex cells of each individual. A) Independent Assortment: the way the different pairs line up in relation to other pairs during metaphase I, leading to many possible combinations in the sex cells that result.

5 B) Crossing Over: When the chromosome pairs (one chromosome from mom. 1 from dad) parts during prophase I. When they separate, genes are. All 4 cells will now carry combinations of information. No two sperm cells or egg cells are alike! Origin of new combinations of inheritable traits in offspring & the reason why there s within a species Why does this allow a species to evolve? VI. Problems during Meiotic Division Recall that occurs during Anaphase I, which is when the chromosome pairs are evenly separate. If this does not properly occur, occurs. This results in one sex cell having the amount of chromosomes. An example of a disorder caused by nondisjunction is. Each body cell will have an extra chromosome