Do Now #1 • A cell containing both sets of homologous chromosomes is said to be ______ , meaning “two sets”. • Cells that contain a single set of chromosomes is called _____. • Where can animal cells that contain only one set of chromosomes be found? Do Now # 2 Calculating Haploid & Diploid Numbers Organisms Haploid Number Amoeba N=25 Chimpanzee N=24 Earthworm N=18 Fern Diploid Number 2N=1010 Hamster N=22 Honeybee N=28 Human N=23 Onion N=8 Do Now # 3 HINT: The colored arrows represent the ploidy (sets of chromosomes). Do Now # 4 After Meiosis I, are the cells haploid or diploid? Spindle fibers Nucleus Nuclear envelope Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Anaphase I (diploid) Telophase I (diploid) Why do you share some, not all traits of each parent? Goal of Meiosis: reduce genetic material by half Why? from mom from dad child too much! meiosis reduces genetic content How are haploid gamete cells produced from diploid cells? Overview of Meiosis • Two Cell Divisions (Meiosis I & II) • Begin with 1 diploid cell • End with 4 haploid cells • Provides variation • Interphase • Meiosis I Prophase I Metaphase I Anaphase I Telophase I Cytokinesis • Meiosis II Prophase II Metaphase II Anaphase II Telophase II Cytokinesis The Key Difference Between Mitosis and Meiosis is the Way Chromosomes Uniquely Pair and Align in Meiosis Mitosis The 1st division of meiosis Meiosis I Spindle fibers Nucleus Prophase I (early) (diploid) Prophase I (late) (diploid) Metaphase I (diploid) Nuclear envelope Anaphase I (diploid) Telophase I (haploid) What do you see? Early prophase Prophase I Late prophase Meiosis Makes a Variety of Different Sex Cells – Crossing-Over Crossing-over multiplies the already huge number of different gamete types produced by independent assortment. Crossing-over • Occurs in prophase of meiosis I A A B B C • Generates diversity b C D D E F E F • Creates chromosomes with new combinations of alleles for genes A to F. a a c b c d d e f e f Crossing-over • Occurs in prophase of meiosis I A a B C • Generates diversity Letters denote genes Case denotes alleles C c D D E F d E F e f b c d e f •Creates chromosomes with new combinations of alleles for genes A to F. Crossing-over • Occurs in prophase of meiosis I a A B C C D D • Generates diversity Letters denote genes Case denotes alleles E F b E F A a B c b c d d e f Creates chromosomes with new combinations of alleles for genes A to F. e f What do you see? Metaphase I Remember what happened during Mitosis metaphase What do you see? Anaphase I Remember what happened during Mitosis anaphase What do you see? Telophase I Meiosis II Prophase II (haploid) Metaphase II (haploid) Anaphase II (haploid) Telophase II (haploid) Four nonidentical haploid daughter cells What do you see? Prophase II What do you see? Metaphase II What do you see? Anaphase II What do you see? Telophase II What do you see? Results of meiosis Cells alive! • Gametes • Four haploid cells • One copy of each chromosome, instead of a pair • DIVERSITY Mitosis # Cell Divisions Where Role Sets of Genetic Material # of Daughter Cells Produced Genetically Identical Similarities Meiosis Oogenesis First polar body may divide (haploid) a Mitosis Oogonium (diploid) A X Polar bodies die X Meiosis I Meiosis II X Primary oocyte (diploid) X a X a a A X A X Secondary oocyte (haploid) Ovum (egg) A X Second polar body (haploid) Mature egg Spermatogenesis: sperm formation “Putting It All Together” - Fertilization Meiosis is All About… allowing the creation of unique individuals through sexual reproduction. Why are we so unique? Independent assortment The homolog of one chromosome can be inherited with either homolog of a second chromosome. Random assortment The combination of maternal and parental chromosomes received by a gamete is random. And we have 23 pairs of chromosomes The possible combinations in an egg or a sperm are: 223 = # of combinations in an offspring 223 x 223 = This doesn’t included crossing-over! Review Meiosis • • • • Meiosis Animation with Quiz Step by Step Meiosis at Cells Alive! Step by Step Animations with Text Shockwave Video Can mistakes happen ? Is this a female or male karyotype? Turner’s Syndrome: monosomy • Female XO • 1/2,500 – 1/3,000 • Underdeveloped female characteristics – Short stature – Broad chest – Horseshoe kidney - absence of period (amenorrhea) - infertile • 98% are spontaneously aborted -miscarriage Uniparental disomy • Two copies of the chromosome are from one parent. • Rare recessive disorders can arise; otherwise no physical anomalies. – Prader-Willie Syndrome – Angelman Syndrome • 1/800-1000 births • Extra copy of chromosome 21 • 47 chromosomes total • Amniocentesis Down Syndrome Klinefelter's syndrome • XXY • Most common sex chromosome disorder • 1 out of 750 males • 47 chromosomes • Sterile Male with some female characteristics Triple X Syndrome • XXX • 1 in 1,000 females • Normal sexual development • Typically fertile Fertilization What is fertilization? – The fusion of egg & sperm – Restores the species # of chromosomes – Creates a ZYGOTE What are the advantages & disadvantages for both? External Fertilization vs. Internal Fertilization
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