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Lecture 1Plant breeding – genetic modificationThe Green Revolution – the application of basic genetic principles life in many parts of the developing world was transformed – many deaths avoidedEugenics – the self-direction of human evolutionControlling breeding“Eugenical Sterilization Act”Nazi Euthanasia – based on genetic principles - Transmission Genetics  from understanding mitosis and meiosiso Mitosis – faithful duplication and transmission of genomes during cell division Consider cell numbers – human: tens of trillions (million million) Consider genome sizes – human: n=3 billion bp Consider consequences of errors- Cell death- Diseaseo Eukaryotes Haploid/ diploid Homologous chromosomes-  Chromosome structure-- Know: centromere, telomere, kinetochore, microtubules, chromatids, sister chromatids, chromosomes Cell cycle-- G1, S, G2 (all 3 – interphase), M (mitosis)- Prophase – chromosome condensation, spindle formation- Prometaphase – nuclear membrane melts, condensed chromosomesbegin to align at midline- Metaphase – chromosomes aligned, spindles attaches to kinetochores- Anaphase – sister chromatids separates and move to poles- Telophase – nuclear membrane reforms, chromosomes decondense--- Errors in mitosis and human diseases and disorderso Non-disjunction – failure of sister chromatids to separate during anaphase (somies, trisomies, nulosomies)o Unregulated Cell Division  cancerMitosis/Meiosis Review- Eukaryotic specie have a characteristic number of chromosomes per cello Humans – 46 chromosomeso No relationship between complexity of organism and number of chromosomes percello Two sets of chromosomes, one inherited from male one from female parent =homologous pair Humans – 23 homologous pairso Most cells carry two sets of genetic information  diploido Reproductive cells contain a single set of chromosomes  haploid One copy of each gene- Parts of a chromosomeo Centromere – attachment point for spindle microtubuleso Telomere – tip of a linear piece of chromosomeo Origin of Replication – sites where DNA synthesis begins- Cell Cycle and MITOSISo 2 phases: Interphase and M phaseo Interphase – between cell divisions, cell grows, develops, and functionso M phase – period of active cell divisiono Interphase (checkpoints and subphases) G1: the cell grows G1/S checkpoint: holds cell in G1 until it has all enzyme necessary for DNA replication- Before this cells can exit from active cycle and pass into nondividing phase called G0 which is a stable state during which cells usually maintain a constant size, can reenter active or stay in G0- If pass checkpoint they are committed to divide S phase: DNA synthesis  each chromosome duplicates G2 G2/M checkpoint: passed only is the cells DNA is undamaged Throughout interphase chromosomes are relaxed by not uncoiledo M phase Copies of the cells chromosomes (sister chromatids) separate and the cell undergoes division 6 stages (5 stages of mitosis and cytokinesis) Prophase- Chromosomes condense- Duplication occurred during S phase but now can visibly see the two chromatids attached at the centromere- Spindles form Prometaphase- Disintegration of the nuclear membrane- Microtubules make contact with the chromosomes at kinetochore Metaphase- Chromosomes align in the center of the cell- Spindles come from each end of the cell and attach to chromatids Anaphase- Connection between sister chromatids separate- Chromosomes move toward opposite spindle poles Telophase- Chromatids have separated and each is considered a separate chromosome  arrived at spindle poles- Nuclear membrane re-forms around each set of chromosomes Cytokinesis – Division of the cytoplasm- Sexual Reproductiono 2 processes: Meiosis (leads to gametes and chromosomes number is half) and Fertilization (two haploid gametes fuse and restore chromosome number to original diploid value)- MEIOSISo 2 divisions after each meiosis (I and II)o Meiosis I Interphase Prophase I - Homologous chromosomes synapse (close pairing) and condense- Crossing over takes place  homologous chromosomes exchange genetic information Metaphase I – line up Anaphase I – two chromatids separate Telophase – Chromosomes arrive at spindle poledo Meiosis II Prophase II – chromosomes condense, spindles re-forms, membrane breaks down Metaphase II – individual chromosomes line up on the metaphase plate with sister chromatids facing opposite poles Anaphase II – sister chromatids are pulled to opposite poles Telophase II  Haploid numberLecture 2- Genetic Variation is the key to survival (must constantly evolve because being chased by pathogens and parasites)o Red Queen Hypothesis – keep running to stay in place- Meiosis is the key to sex – halves the size of genome and places it in a gamete so it can be recombined with another gamete to restore the normal genome size- Transmission Genetics:- Karyotype – a set of chromosomes as seen during cell division (number, size, shape, staining, patterns)o Our karyotype is 22 pairs of chromosomes plus X and/or Y- Sex  Genetic Variationo Two parents = many different combination of progeny (humans)o 223x223= 71,000,000,000,000 combinationso Sex requires halving chromosome number of parents so sexual reproduction results in constant chromosome number = meiosis Each product of meiosis receives 1 copy of all chromosomes- Cell Cycleo DNA replication during So 2 Phases of Meiosis Phase I (Meiosis I): reducing chromosome number Phase II (Meiosis II): separating sister chromatidsoooo Meiosis I: Reduction division Prophase I-- Longest, most complex phase - Leptotene, zygotene, pachytene, diplotene, diakinesis- Chromosome pairing – homologous pairing- Crossing over – syaptonemal complex, chiasmata, bivalent (tetrad)o Chiasma – exchange of DNA strands has occurred Can visually see the crossing over = chiasma- Crossing over – chromosome shuffling – variation generation Metaphase I- Homologous pairs along midline- Kinetochores attached to one pole- Chance alignment relative to poles (underlies genetic principle of Independent Assortment)- Cohesion keeps sister chromatids together – regulating cohesion is key to successful meiosis- Anaphase I, Telophase Io Meiosis II: Separation of sister chromatids Prophase II – condensation Metaphase II- Centromeres along midline-

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UMD BSCI 222 - Lecture 1

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