Chapter 13 Notes MEIOSIS

4 daughter cells that are haploid all of them are

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Unformatted text preview: 4 daughter cells that are haploid ALL OF THEM ARE GENETICALLY DIFFERENT! critical for growth critical for reproduction Three(events(unique(to(meiosis(occur(during(meiosis(I( ! 1.  Synapsis!and!crossing!over! 2.  Homologs line up at metaphase plate !!!!! 3.  Homologs!separate!during!anaphase!I! Why(are(these(events(important?( ! GENETIC VARIABILITY!!!!!!!!!! These differences are important because it is during these events that genetic variation is generated in gametes --- crossing over and lining up of the homologs does this! How(do(we(account(for(gene;c(varia;on(in(offspring(for(organisms(that(reproduce(sexually?( 1.  Independent!Assortment!of!Chromosomes! This happens in meiosis, the generation of gametes 2.  Crossing!Over! 3.  Random!Fer8liza8on! You never know which sperm is going to fertilize which egg -- it's all random Each chromosome can line up independently of the other chromosomes During(Metaphase(I(–(homologs(line(up(on(the(metaphase(plate( HOW they align is completely random!!! can be like this... 50% chance it'll align on left side Chromosome(1( Chromosome(2( …or like this Metaphase(I( Two!equal!probable!arrangements!of! chromosomes!(right!or!leQ)! Each!chromosome!aligns!independent! Chromosome(1( Chromosome(2( 50% chance it'll align on right Metaphase(II(((((( Daughter(Cells( ! Combina8on(1(( all(paternal( This combo happens to have them ALL paternal Combina8on(2(( all(maternal( Combina8on(3(( Chromosome(1(paternal( Chromosome(2(maternal( This combo has paternal and maternal chromosomes Can(quan;fy(the(number(of(possible(combina;ons=( Combina8on(4(( Chromosome(1(maternal( Chromosome(2(paternal( 2^n -- n is the # of chromosome pairs Hypothe;cal(Example:((Look!at!my!daughter’s!karyotype!and!focus!on!two!traits!(chin!shape! and!eyebrow!thickness)! ! Make!the!assump8on!that!only!one!gene!codes!for!chin!shape!and!only!one!gene!codes!for! eyebrow!thickness! Paternal! Chromosome! ! R!and!r!are!alleles!for! chin!shape!gene! B!and!b!are!alleles!f...
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