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Genetics Why do we look the way we do? Inheritance of chromosomes • Egg + sperm zygote egg zygote sperm How does this work? • Paired chromosomes have ___________________ – but __________________________ eye color (blue?) hair color eye color (brown?) hair color What did we show here? • Genes come in “versions” – brown vs. blue eye color – ___________________ • Alleles are inherited separately from each parent – brown & blue eye colors are separate & do not blend • either have brown or blue eyes, not a blend • Some alleles mask others – brown eye color masked blue Traits are inherited as separate units • For each trait, an organism inherits _________________________________________ – a __________________ organism inherits 1 set of chromosomes from each parent • __________________________________ 1 from Mom 1 from Dad Making gametes BB = brown eyes bb = blues eyes Bb = brown eyes B BB B b bb b B Bb Remember meiosis! b How do we say it? B BB B BB = brown eyes bb = blues eyes b bb b B Bb Bb = brown eyes b Punnett squares x Bb male / sperm X female / eggs Bb B b BB Bb Bb bb B b Genetics vs. appearance • There can be a difference between how an organism looks & its genetics – appearance or trait = ________________ • brown eyes vs. blue eyes – genetic makeup = _________________ • BB, Bb, bb 2 people can have the same appearance but have different genetics: Genetics vs. appearance How were these brown eyes made? eye color (brown) eye color (brown) eye color (brown) eye color (blue) vs. B BB B Bb B b Meiosis Homologous Chromosomes • Chromosomes that have a corresponding partner from each parent. Paired chromosomes • Homologous chromosomes – both chromosomes of a pair carry ________________ • control same inherited characters • ____________________________________ diploid 2n 2n = 4 eye color (brown?) eye color (blue?) homologous chromosomes double stranded homologous chromosomes Cell division / Asexual reproduction • Mitosis – produce cells with __________________ • identical daughter cells – ___________________ • clones – ____________________________ • same genetic information Aaaargh! I’m seeing double! Asexual reproduction • Single-celled eukaryotes – yeast – Paramecium – Amoeba • Simple multicellular eukaryotes – Hydra • budding What are the disadvantages of asexual reproduction? What are the advantages? Haploid vs. Diploid • A cell that contains only one set of chromosomes is _________________________ • A cell that contains both sets of homologous chromosomes is ________________________ How about the rest of us? • What if a complex multicellular organism (like us) wants to reproduce? – joining of egg + sperm • Do we make egg & sperm by mitosis? What if we did, then…. 46 egg + 46 92 sperm zygote Meiosis Goal: Reduce genetic material by half Why? from mom from dad meiosis reduces numbers of chromosomes by half child How do we make sperm & eggs? • Must reduce 46 chromosomes 23 – must ______________ the number of chromosomes – ______________ 46 23 zygote 23 46 egg 23 46 23 sperm gametes Meiosis makes sperm & eggs • 46 chromosomes to 23 chromosomes – half the number of chromosomes 46 23 egg 46 23 sperm Meiosis = reduction division • Meiosis – special cell division in sexually reproducing organisms – _______________________________ • _________________ • _________________ – half – makes _____________ • sperm, eggs Meiosis: two cell divisions homologous Chromosomes separate Sister chromatids separate Result: ONLY one copy of each chromosome in a gamete. Meiosis 1 overview double stranded Divide 1 • 1st division of meiosis Line Up 1 prophase 1 metaphase 1 telophase 1 gamete Meiosis I : the reduction division (2n Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (haploid) n) Telophase I (haploid) Homologous chromosomes___________ __________________________ . Crossing over creates ____________ Meiosis II Gene X Meiosis II produces gametes with one copy of each chromosome (thus one copy of each gene) Bye Bye 2 Meiosis 2 overview telophase 2 telophase 1 Line Up 2 metaphase 2 4 Meiosis II : the equal division Prophase II (haploid x 2) Metaphase II (haploid x 2) Anaphase II (haploid) Telophase II (haploid) Sperm and Egg formation The value of meiosis 1 • Consistency over time – meiosis __________________________________________ from generation to generation from Mom Mom Dad offspring from Dad We’re The value of meiosis 2mixing things up here! • Change over time – meiosis _______________________________ • gametes of offspring do not have same genes as gametes from parents • new combinations of traits from Dad from Mom offspring How does this explain: family resemblance & differences! Why are the kids so similar to the parents but exact? not Michael & Kirk Douglas Baldwin brothers Martin & Charlie Sheen, Emilio Estevez “Putting It All Together” - Fertilization Putting it all together… gametes 46 23 23 egg 23 46 23 sperm 46 46 46 46 46 46 46 46 46 zygote What Meiosis is About Meiosis allows the creation of unique individuals through sexual reproduction. Meiosis & mitosis • Meiosis to make gametes – ___________________ • Mitosis to make copies of cells – __________ – __________ – __________ MITOSIS MEIOSIS Produces cells for repair, maintenance, growth, asexual reproduction Only produces gametessex cells (egg/sperm) Results in Reduction division results in Mitosis # of divisions # of daughter cells Genetically identical? Chromosome # Where When Role Meiosis