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3/25/2013 LIVING ORGANISMS 2 types of cells: Autosomal (body) cells have 2 copies of every gene Gametes (sex) cells have 1 copy of every gene MEIOSIS Genetics Unit CHROMOSOME NUMBER Autosomal (body) cells Gametes (sex) cells Humans 46 Sperm & Egg cells Female XX Male XY Willie Shoemaker, Wilt Chamberlain ~taken by Annie Liebowitz 1 3/25/2013 SEXUAL REPRODUCTION WHAT IS INHERITED? Sexual reproduction provides variation due to the shuffling and recombination of alleles during meiosis and fertilization 99.99% of our DNA is the same MEIOSIS is what makes us different! WHY MEIOSIS? 3/20/13 Cell division to make gametes, or sex cells Sperm in males Eggs in females Why would it be different than Mitosis? Diploid (2n) – contains a pair of each chromosome; mitosis Haploid (n) – contains only 1 of each chromosome; meiosis Genes – sequence of DNA, that codes for a protein, that determines a trait Genes are located on chromosomes (supercoiled DNA) Humans have 46, or 23 “homologous” pairs Half from mom, Half from Dad Objective Illustrate the steps to meiosis Warm-Up 1. Multiply (x + 5)(x – 5) 2. How many copies of a gene do body (autosomal) cells have? How many do sex (gamete) cells have? EX. 2N = 4 MEIOSIS I Prophase I Tetrads form – homologous chromosomes pair Cross-Over occurs – homologous chromosomes exchange part of their chromatin Produces new gene combinations! All other events same as mitosis 2 3/25/2013 GENETIC VARIATION: CROSSING OVER Homologous chromosomes group together and exchange pieces. Meiosis I Crossing over MEIOSIS I Metaphase I Tetrads line up randomly on the metaphase plate Increases variation! Anaphase I Homologous chromosomes are pulled apart http://www.youtube.com/watch?v=D1_mQS_FZ0&feature=related MEIOSIS I Telophase I Same events as in mitosis EXCEPT… now the daughter cells are Haploid Meiosis I Interphase I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis MEIOSIS II Exactly like Mitosis; sister chromatids separate Telophase I and Cytokinesis I Meiosis II Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis 3 3/25/2013 MEIOSIS Four haploid cells (n) each have one chromosome. Each cell has a different combination of alleles. GENETIC VARIATION: PRINCIPLE OF INDEPENDENT ASSORTMENT GENETIC VARIATION: RANDOM FERTILIZATION HUMANS There is a 50% chance that a particular gamete will receive a maternal chromosome and a 50% chance it will receive a paternal chromosome. There are 23 pairs of chromosomes in human games cells. Number of possible combinations of maternal and paternal chromosomes= 223 Many possible combinations of male and female gametes. HUMANS One human ovum (egg) represents approximately 8 million possible chromsome combinations. Same is true for sperm. Thus, one sperm fertilizing one egg results in 8 million x 8 million recombination possibilities 4 3/25/2013 MEIOSIS SQUARE DANCE MEIOSIS FOLDABLE http://teachersites.schoolworld.com/webpages/DC urry/life.cfm?subpage=1151190 MALES VS. FEMALES 3/22/13 Males produce 4 haploid gametes (sperm) Females produce 1 haploid gamete (egg) + 3 “polar bodies” 3/25/13 Objective Illustrate meiosis Warm-Up Subtract (5p2 – 3) – (2p3 – 3p2) What happens during prophase I that allows for genetic variation? AIMS is just around the corner! Objectives Differentiate between mitosis and meiosis Warm-Up 1. Simplify (2m2)(2m3) 2. What is the goal of meiosis I? 3. What is the goal of meiosis II? MITOSIS VS. MEIOSIS 5 3/25/2013 EX. 2N = 4 MITOSIS VS. MEIOSIS Mitosis Meiosis Type of cell Body Cell Sex cell Beginning cell Diploid (2n) Diploid (2n) Ending cell Diploid (2n) Haploid (n) # of cells produced 2 4 # of chromosomes Same as parent cell Half as parent cell Haploid Diploid Purpose To make more body cells To make egg and sperm *Cross-Over *Random Orientation Haploid Identical Different MITOSIS VS. MEIOSIS Meiosis: MEIOSIS LAB Random orientation of chromosomes Crossing over Random fertilization Independent assortment Occurs in 2 phases Creates 4 different cells (haploid) Mitosis: Creates 2 genetically identical cells (diploid) PRACTICE A human has 23 pairs of chromosomes. 1. What is the diploid number? 2. What is the haploid number? 3. How many chromosomes are in an egg cell? 4. How many chromosomes are in a brain cell? 5. How many chromosomes are in a skin cell? 6. How many pairs of homologous chromosomes? 7. How many chromosomes in a cell produced by mitosis? 8. How many chromosomes in a cell produced by meiosis? MEIOSIS OREO COOKIE LAB PICTURES 6 3/25/2013 COOKIES Blue: 1 Pair of Homologous Chromosomes Pink: 1 Pair of Homologous Chromosomes Red: Nuclear Envelope Green: Meiotic Spindles Brown: Centrioles PROPHASE I METAPHASE I COMPLETED Blue: 1 Pair of Homologous Chromosomes Pink: 1 Pair of Homologous Chromosomes Red: Nuclear Envelope Green: Meiotic Spindles Brown: Centrioles OREO COOKIE LAB ANAPHASE I TELOPHASE I ANAPHASE II TELOPHASE II Random orientation Crossover PROPHASE II METAPHASE II 7 3/25/2013 PROBLEMS WITH MEIOSIS THIS IS WHAT YOUR CHROMOSOMES LIKE DURING MITOSIS. Scientists take a picture of the chromosomes, like this one, and cut then them out… Nondisjunction …AND THEN GROUP THEM TOGETHER BY SIZE. KARYOTYPES Karyotype – picture of chromosomes grouped as pairs CALLED AN AMNIOCENTESIS. Humans-46 chromosomes; 23 pairs PROBLEMS SHOW UP WHEN THE BABY HAS THE WRONG NUMBER OF CHROMOSOMES. LOOK ARE MADE MOST OFTEN DURING PREGNANCY IN A PROCEDURE Amniocentesis – The baby’s amniotic fluid cells are taken from the womb through a needle, and a karyotype is made to look for disorders. THIS KARYOTYPE SHOWS THAT THE 21. THIS CAUSES THE BIRTH DEFECT DOWN SYNDROME. PERSON HAS THREE OF CHROMOSOME What is wrong with this karyotype? 8 3/25/2013 DOWN SYNDROME – “TRISOMY 21” Children with Down Syndrome have a variety of problems, including mild mental retardation, heart problems, and many other unusual physical characteristics. Nondisjunction – When chromosomes fail to separate during meiosis. Down Syndrome occurs when two sister chromatids fail to separate during anaphase of meiosis II. As a result, some of the eggs or sperm produced have too many chromosomes. When a cell ends up with three copies of a chromosome instead of two, this is called trisomy. If a cell has only one copy, this is called monosomy. OTHER NONDISJUNCTION DISORDERS: Triple X Syndrome Turner’s Syndrome (XXX) (X__) Edward Syndrome (trisomy Klinefelter’s Syndrome (XXY) 18) Males w/an X Girls w/3 X extra chromosomes Girls w/1 X Only 5-10% of live births fertility survive the Small testicles, reduced Tall, but normal physical and st year stature, swelling, sterility 1Short of life sexual characteristics Many abnormalities in internal organs and external Increased risk of structures learning disabilities Slow speech and motor development NONDISJUNCTION IS MOST LIKELY TO HAPPEN IN OLDER MOTHERS, BECAUSE THEIR EGGS HAVE BEEN IN THEIR BODIES SINCE BEFORE BIRTH, AND ARE MORE LIKELY TO HAVE PROBLEMS DIVIDING. 9 3/25/2013 KARYOTYPING ACTIVITY Map each karyotype and determine if it is male or female? What is its genetic disorder? Options: Klinfelter’s syndrome (XXY) Edward’s syndrome (trisomy 18) Down syndrome (trisomy 21) Trisomy 13 10