Chapter 13 Notes MEIOSIS

Recombinantchromosomesthatcarrygenesfrombothpaternalan

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Unformatted text preview: om!both!paternal!and! maternal!chromosomes! ! *! In humans, an average of one to two crossover events occurs per chromosome pair depending on the size of the chromosomes and the position of their centromeres Replicate(during(Interphase(I( Paternal(Chromosome( a((b((c((d((e((f((g( a((b((c((d((e((f((g( A((B((C((D((E((F((G( A((B((C((D((E((F((G( Contains!genes!! A!V!G! Maternal(Chromosome( Contains!genes!! a!–!g! Same!genes! Different!alleles! Synapsis(occurs(during(Prophase(I( Paternal(Chromosome( Maternal(Chromosome( a((b((c((d((e((f((g( a((b((c((d((e((f((g( A((B((C((D((E((F((G( A((B((C((D((E((F((G( If(crossing(over(occurs(here( Between(these(two(nonsister(chroma8d(( What(alleles(will(the(resul;ng(chroma;ds(contain?( a B b c C d D e E f g F G a((b((c((d(((e((f((g( A((B((C((D((E((F((G( All(Paternal( A Unique(combina8on( of(Paternal(and( Maternal( Unique(combina8on( of(Paternal(and( Maternal( All(Maternal( Mechanics(of(crossing(over:( Nonsister!chroma8ds!held! together!during!synapsis! Pair!of!homologs! Chiasma!! site!of! crossing!over! Centromere! Centromere! There can be crossing over of non-sister chromatids as well but they don't usually show this In!prophase!I,!synapsis!and!crossing!over!occur;! then!homologs!move!apart!slightly! ! *! Chiasmata and attachments bw sister chromatids hold homologs together as they move to metaphse plate ! ! ! ! During!anaphase!I,!breakdown!of!proteins!holding! sister!chroma8d!arms!together!allows!homologs! with!recombinant!chroma8ds!to!separate!!! ( Note:( During anaphase I, cohesion bw sister chromatids at centromere is protected ( ! ! During!anaphase!II,!breakdown!of!proteins!holding! sister!chroma8ds!together!at!the!centromere!takes! place!and!sister!chroma8ds!separate! Random(Fer;liza;on( Sperm! Egg((=(1!in!8.4!million!possible!gamete!combina8ons( ( Sperm(=((1!in!8.4!million!possible!gamete!combina8ons! Egg! Zygote(=! ! 70 trillion (2^23 x 2^23) possible combos!!!! BUT…that's not all! Don't forget about the crossing over that can't be quant...
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