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What do these 3 people have in common? Arthur Shawcross: The Genesee River Killer. In March 1988, he murdered 11 females often dumping their bodies in the Genessee River in Rochester, NY. John Wayne Gacy: The Killer Clown Between 1972 and 1978, he murdered 33 boys and young men, 27 of whom were found buried under the floor of his house. Bobbie Joe Long During an 8 month period in 1984, he murdered at least ten women in Tampa Bay area of Florida. The murders were extremely brutal. They are all American serial killers!!! What else do these 3 people have in common? They all have a genetic disorder called XYY syndrome, which resulted from each of them receiving an extra Y chromosome from his father. (normal male = XY) The XYY syndrome was previously considered the "supermale" syndrome where men with this condition were thought to be overly aggressive and more likely to become a criminal. These original stereotypes came about because several researchers in the 1960s found a high number of men with XYY syndrome in prisons and mental institutes. Based on these observations, men with XYY syndrome were labeled as overly aggressive and likely to be criminals. It is now believed that though there is a disproportionate number of men in prison with XYY Syndrome compared to the normal population. However, the numbers still are not high enough to indicate that the syndrome is linked directly with violence. A Karyotype of an XYY Person 2Y chromosomes How is this related to biology? In order to get XYY syndrome, some biological error must have happened that caused the individual to end up with an extra Y chromosome – What do you think may have happened to cause this error? – What process do you think was involved? Start with 4 chromosomes Section 11-4: Meiosis The word "meiosis" comes from the Greek meioun, meaning "to make small," since it results in a reduction in chromosome number in the gamete cell. End with 2 chromosomes A. Why is Meiosis Important? Consider these Questions … 1. How many chromosomes would a human sperm or an egg contain if either one resulted from the process of mitosis? a. 46 chromosomes 2. If a sperm containing 46 chromosomes fused with an egg containing 46 chromosomes, how many chromosomes would the resulting fertilized egg contain? Do you think this would create any problems in the developing embryo? b. 46 + 46 = 92; a developing embryo would not survive if it contained 92 chromosomes. 3. In order to produce a fertilized egg with the appropriate number of chromosomes (46), how many chromosomes should each sperm and egg have? c. Sperm and egg should each have 23 chromosomes. *Meiosis how you make sperm and egg cells with only 23 chromosomes* B. Chromosome Number 1. Number varies by organism – a. Ex: turkey 82, fruit fly 6, human 46 2. Organisms that reproduce sexually have pairs of similar chromosomes – a. Called HOMOLOGOUS CHROMOSOMES – b. Similar in size, structure, and carry genes for the same traits (but may be different forms of the gene) – c. Each member of a pair comes from each parent – d. Ex: humans have 23 pairs of homologous chromosomes, or 46 total i. 23 in sperm, 23 in egg, pair up 3. Diploid vs. Haploid a. Diploid – i. Double set of chromosomes – ii. “2n” – iii. Humans – 23 sets/pairs, 2n = 46 b. Haploid – i.. Single set of chromosomes – ii. “n” – iii. Humans – one chromo. from each set, n = 23 4. Chromosome numbers & cell types a. Somatic cells – i. “Regular” body cells – ii. Always diploid – iii. Humans 46 chromo. b. Gametes – i. “sex cells” – ii. Usually egg & sperm (or pollen/spores) – iii. Always haploid – iv. Humans 23 chromo. C. Phases of Meiosis Meiosis I 1. Interphase I – a. Cells undergo a round of DNA replication, forming duplicate chromosomes 2. Prophase I – a. Each chromosome pairs with its corresponding homologous chromosome to form a tetrad i. tetrad contains 4 chromatids – b. Homologous chromosomes exchange portions of their chromatids ii. Called crossing over tetrad crossing-over Crossing-Over 3. Metaphase I – a. Spindle fibers attach to the chromosomes – b. Tetrads line up in the middle of the cell 4. Anaphase I – a. Fibers pull homologous chromosomes toward opposite ends of the cell – b. Centromere stays intact 5. Telophase I and Cytokinesis – a. Nuclear membranes form – b. Cell separates into 2 cells Meiosis II 1. Prophase II – a. Meiosis I results in 2 haploid (N) daughter cells each with half the number of homologous chromosomes as the original cell 2. Metaphase II – a. Chromosomes line up in the center of the cell 3. Anaphase II – a. Paired sister chromatids separate and move towards opposite ends of the cell – b. Centromere is broken 4. Telophase II and Cytokinesis – a. Meiosis II results in 4 haploid (N) daughter cells – b. Each cell contains half the number of chromosomes as the original cell Meiosis I Tetrad = 4 chromatids Homologous chromosome Meiosis II Prophase II Metaphase II Meiosis I results in two The chromosomes line up in a haploid (N) daughter cells, similar way to the metaphase each with half the number of stage of mitosis. chromosomes as the original. Anaphase II The sister chromatids separate and move toward opposite ends of the cell. Telophase II Meiosis II results in four haploid (N) daughter cells. D. Gamete Formation Unequal division of cytoplasm 1. Males 4 sperm formed 2. Females 1 egg formed (larger) and 2 polar bodies (smaller) a. only the egg is used in reproduction E. Comparing Mitosis and Meiosis Mitosis 1. Known as cell division 2. Consists of 1 division 3. Forms 2 genetically identical daughter cells 4. Daughter cells have same amount of chromosomes as parent cell (humans = 46) 5. Occurs only in body cells – somatic cells 6. Purpose = make more body cells for growth and repair Meiosis 1. Known as cell reduction division 2. Consists of 2 divisions 3. Forms 4 genetically different daughter cells 4. Daughter cells have half the amount of chromosomes as the parent cell (humans = 23) 5. Occurs only in sex cells – gametes 6. Purpose = form egg and sperm cells for fertilization Meiosis Animations 1. Meiosis Overview 2. Animal Cell Meiosis (Part 1) 3. Animal Cell Meiosis (Part 2) 4. Crossing Over