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Sexual Reproduction Heredity Heredity - passing down of characteristics ( genes genes) Alleles Alleles- different forms of the same gene

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  • Sexual ReproductionHeredity - passing down of characteristics (genes)

    Alleles- different forms of the same gene

  • Sexual ReproductionWhy sexual reproduction? shuffles alleles; new combinationsprovides genetic variation in species

  • MeiosisType of cell division One germ* cell makes 4 gametes (egg/sperm) with the # of chromosomes.

    Occurs only in germ* cells of gonads testes /ovariesOccurs in flowers ovary and anther *Germ here doesnt mean bacteria. Its a term used for the type cells that gives rise to gametes in organisms.

  • While females are born with all the eggs they will ever have (around 400,000), only about 400 will ever mature and ovulate between puberty and menopause.

  • Matrue males produce about 100 million sperm each day.

  • Sperm surrounding an egg

  • This shows how only one single sperm gets to penetrate the egg, releasing its nucleus of 23 chromosomes to merge with the nucleus of the egg and its 23 chromosomes.

  • Homologous ChromosomesPair of chrom. similar in shape , size, and types of genes.Each locus (location of the gene) in same position on chrom.

    Humans have 23 pairs of homologuesHousefly 6 prs Chicken 39 prs Apple 17 prsDog 39 prsCat 19 prs

    This is a karyotype (an image of an organisms chromosomes)

    This is a karyotype of a normal human male

  • Chromosome numbers:However many types of chrom. an organism has, that number is the n number of chrom. it has.

    Body cellsEgg/Sperm cellsCalled:Somatic cellsGametesTerm for chrom. #Diploid (2 sets of chrom.)Haploid (1 set of chrom.)n number2n1nFor Humans:46 chrom.23 chrom.

  • Homologous Chromosomes

  • AnimationMeiosis A animationMeiosis B animationMeiosis C animation

  • Prophase ILongest and most complex phase (90% of meiosis).DNA condenses into chromosomes.Synapsis - a process: when homologous chrom. come together, pair up, form a tetrad.

  • Prophase I - Synapsis Nonsister chromatids

  • Prophase I - Crossing OverCrossing over may occur in the tetrad: between nonsister chromatids, ends break and reattach

  • Crossing Over - Provides Variation variation

  • Metaphase IShortest phase; paired homologues align.INDEPENDENT ASSORTMENT occurs pairs of homologues line up independently of other pairs orientation toward the poles -- random. Adds variation.

  • Anaphase IHomologous chromosomes separate towards the poles (Tetrads separate)

    Sister chromatids remain attached

  • Telophase IEach pole now has haploid set of chromosomes (however still doubled).Cytokinesis occurs: two haploid daughter cells formed.

  • Meiosis IINo interphase II ( no more DNA replication)Remember: Meiosis II is similar to mitosisProphase II / Metaphase IIAnaphase II

  • Telophase IISame as telophase in mitosis.Nuclei form.Cytokinesis occurs (2nd time).Four haploid daughter cells produced (chromosomes now back to single condition).gametes ~ sperm or egg; ovule or pollen grain

  • Gamete Formation in AnimalsDiff. bet. male and female gametes.

    Male: spermatogenesis all 4 develop into sperm cells. Female: oogenesiscytokinesis is uneven. most cytoplasm goes to 1 of the 4 eggs (forms 1 large egg cell) 3 other cells are small polar bodies which die

  • Spermatogenesis

  • Oogenesis2n = 46human germ cellin ovarydiploid (2n)n=23Still doubledn=23Still doubled

    meiosis I232323Ovumn=23Polar Bodiesmeiosis II

  • Mitosis vs MeiosisMitosisBody (somatic cells)2 daughter cells made (identical)Each w/ same # & kind of chrom. as parent cell1 division process 1 cytokinesisNo synapsis or crossing overAre diploid (2n)MeiosisGerm cells of gonads4 gamete cells made (all different)Each w/ chrom. # as parent cell2 divisions2 cytokineses eventsSynapsis & crossing over occurs in Prophase 1Are haploid (n)

  • NondisjunctionWhen the tetrad (in Anaphase I) or the sister chromatids (in Anaphase II) do not separate, creating an abnormal # of chrom. to occur in the gametes.

    Lethal most of the time

  • Karyotype normal male

  • Karyotype normal female

  • Downs SyndromeTrisomy 2147, XY, +21

    The only trisomy survivable to adulthood