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Why do you look a little like your mom and your dad? Why do you look a little like your grandma but your brother or sister looks a little like your grandpa? How is the way you look and act connected to your genes in your DNA? 2 of 35
You get half your DNA from mom You get half your DNA from dad Think about where they got their DNA from? Dad has half from each of his parents and you get half of that. You might get the half from his mom while your brother or sister gets half from his dad 3 of 35
Each organism must inherit a single copy of every gene from each of its parents. Gametes are formed by a process that separates the two sets of genes so that each gamete ends up with just one set. Gametes in males = sperm Gametes in females = egg 4 of 35
Chromosome Number Chromosome Number All organisms have different numbers of chromosomes. 5 of 35
Chromosome Number Chromosome Number Diploid Number = 2N = Full set of chromosomes Haploid Number = N = Half set of chromosomes REMEMBER: Why would organisms ever need to have a half set of chromosomes? 2N = N = 6 of 35
Chromosome Number This is a Karyotype of human chromosomes. These sets of chromosomes are homologous pairs. Each of the 23 chromosomes that came from the male parent has a corresponding chromosome from the female parent. 7 of 35
Chromosome Number A cell that contains both sets of homologous chromosomes is said to be diploid = 2N. For Humans, the diploid number is 46, which can be written as 2N=46. A cell that contains only half of the chromosomes is said to be haploid = N. For Humans, the haploid number is 23, which can be written as N=23. 8 of 35
Chromosome Number The gametes (sperm and eggs) of sexually reproducing organisms contain only a single set of chromosomes, and therefore only a single set of genes. N + N = 2N Humans 23 in sperm + 23 in egg = 46 embryo 9 of 35
Chromosome Numbers Review: Humans have 46 chromosomes 2N = 46 chromosomes How many chromosomes are in the male gamete? N = 23 chromosomes in 1 sperm cell How many chromosomes are in the male gamete? N = 23 chromosomes in 1 egg cell N + N = 2N 23 + 23 = 46 chromosomes EGG + SPERM = Embryo 10 of 35
Chromosome Numbers Another example is Drosophila, the fruit fly. If Drosophilia has 2N = 8 chromosomes then: How many chromosomes are in the male gamete? N = How many chromosomes are in the male gamete? N = N + N = 2N + = 8 chromosomes 11 of 35
Phases of Meiosis So How do we get a cell with Haploid Chromosomes? MEIOSIS! Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell to create haploid cells. 12 of 35
Phases of Meiosis Meiosis involves two divisions, meiosis I and meiosis II. By the end of meiosis II, the diploid cell that entered meiosis has become 4 haploid cells. 13 of 35
11-4 Meiosis 14 of 35
11-4 Meiosis Foldable Meiosis I Meiosis II Prophase I Metaphase I Anaphase I Telophase and Cytokinesis I Prophase II Metaphase II Anaphase II Telophase and Cytokinesis II Description Description Description Description Picture Picture Picture Picture Picture Picture Picture Picture Description Description Description Description Haploid 23 chromosomes Diploid 46 chromosomes Centrioles Crossing over Nuclear envelope Homologous chromosomes Sister chromatids Centromere Tetrad Synapsis Cytokinesis Gamete Sperm Egg Polar bodies 15 of 35
Phases of Meiosis Meiosis I Interphase I Meiosis I Prophase I Metaphase I Anaphase I Telophase I and Cytokinesis 16 of 35
Phases of Meiosis Cells undergo a round of DNA replication, forming duplicate chromosomes. Interphase I 17 of 35
Phases of Meiosis Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. MEIOSIS I Prophase I There are 4 chromatids in a tetrad. 1 from mom + 1 from Dad = 2 Replicate = 4 =Tetrad 18 of 35
Phases of Meiosis IMPORTANT!!!! When homologous chromosomes form tetrads in meiosis I, they exchange portions of their chromatids in a process called crossing over. Crossing-over produces new combinations of alleles. 19 of 35
Phases of Meiosis Spindle fibers attach to the chromosomes tetrads. MEIOSIS I Metaphase I 20 of 35
Phases of Meiosis The fibers pull the homologous chromosomes toward opposite ends of the cell. MEIOSIS I Anaphase I 21 of 35
Phases of Meiosis Nuclear membranes form. The cell separates into two cells. The two cells produced by meiosis I have chromosomes and alleles that are different from each other and from the diploid cell that entered meiosis I. MEIOSIS I Telophase I and Cytokinesis 22 of 35
Phases of Meiosis Meiosis II The two cells produced by meiosis I now enter a second meiotic division. Unlike meiosis I, there is NO chromosome replication. Each of the cell s chromosomes has 2 chromatids. 23 of 35
Phases of Meiosis Meiosis II Telophase I and Cytokinesis I Meiosis II Prophase II Metaphase II Anaphase II Telophase II and Cytokinesis 24 of 35
Phases of Meiosis Meiosis I results in two haploid (N) daughter cells, each with half the number of chromosomes as the original cell. MEIOSIS II Prophase II 25 of 35
Phases of Meiosis The chromosomes line up in the center of cell. MEIOSIS II Metaphase II 26 of 35
Phases of Meiosis The sister chromatids separate and move toward opposite ends of the cell. MEIOSIS II Anaphase II 27 of 35
Phases of Meiosis Meiosis II results in four haploid (N) daughter cells. MEIOSIS II Telophase II and Cytokinesis Failure of chromosomes to separate during meiosis is called non-disjunction. Examples: Turner Syndrome 45,X Klinefelters 47, XXY Down Syndrome Trisomy 23 extra21 chromosome so they have 3 chromosomes 21 28 of 35
Gamete Formation Gamete Formation In male animals, meiosis results in four equal-sized gametes called sperm. 29 of 35
Gamete Formation In many female animals, only one egg results from meiosis. The other three cells, called polar bodies, are usually not involved in reproduction. 30 of 35
Comparing Mitosis and Meiosis Comparing Mitosis and Meiosis Mitosis results in the production of two genetically identical diploid cells. Meiosis produces four genetically different haploid cells. 31 of 35
Mitosis and Meiosis Write this on the back of you foldable. Mitosis Cells produced by mitosis have the same number of chromosomes and alleles as the original cell. Mitosis allows an organism to grow and replace cells. Some organisms reproduce asexually by mitosis. Meiosis Cells produced by meiosis have half the number of chromosomes as the parent cell. These cells are genetically different from the diploid cell and from each other. Meiosis is how sexuallyreproducing organisms produce gametes. 32 of 35
11-4 Continue to: - or - Click to Launch: 33 of 35
11-4 If the body cells of humans contain 46 chromosomes, a single sperm cell should have a. 46 chromosomes. b. 23 chromosomes. c. 92 chromosomes. d. between 23 and 46 chromosomes. 34 of 35
11-4 During meiosis, the number of chromosomes per cell is cut in half through the separation of a. daughter cells. b. homologous chromosomes. c. gametes. d. chromatids. 35 of 35
11-4 The formation of a tetrad occurs during a. anaphase I. b. metaphase II. c. prophase I. d. prophase II. 36 of 35
11-4 In many female animals, meiosis results in the production of a. only 1 egg. b. 1 egg and 3 polar bodies. c. 4 eggs. d. 1 egg and 2 polar bodies. 37 of 35
11-4 Cells in MITOSIS differ from Egg cells in MEIOSIS because they are a. genetically different, while eggs are genetically identical. b. genetically different, just as egg cells are. c. genetically identical, just as egg cells are. d. genetically identical, while egg cells are genetically different. 38 of 35
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