Mitosis vs meiosis: Lecture Outline 10/26/05. Independent Assortment

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1 Lectue Outline 10/26/05 Consequences of meiosis Gmetes e geneticlly vile Inepenent ssotment Cossing ove Lots of pctice polems Eos in meiosis Why epouce sexully? Mitosis vs meiosis: Mitosis ensues exct epliction of the pent cell Meiosis pouces vile, hploi, gmetes. Gmetes e not ienticl, ecuse of: Inepenent ssotment Cossing ove Inepenent ssotment Key Mtenl set of Ptenl set of Possiility 1 Possiility 2 Fo ech pi of, mtenl n ptenl homologues e sote into ughte cells inepenently of the othe pis Two eqully pole ngements of t metphse I Metphse II ughte cells Figue Comintion 1 Comintion 2 Comintion 3 Comintion 4 1

2 Consequences fo genetic vition Consequences fo genetic vition Lel two lleles of gene n e vs white fethes nothe gene on iffeent chomosome: n e vs non-e fethes This iniviul inheite with lleles fo e fethes n non-e fethes its fthe White fethes n e fethes fom its mothe Wht kins of gmetes will it pouce though inepenent ssotment? Cossing Ove Pouces ecominnt tht cy genes eive fom two iffeent pents Pophse I of meiosis Metphse I Tet Nonsiste chomtis Chism, site of cossing ove The loction of cossoves is nom This tet hs 3 cossoves: 2&3 1&3 2&4 Metphse II Figue ughte cells ecominnt Cn occu etween ny pi of chomtis 2

3 Spinle fies fom one pole ttch to OTH siste chomtis Cossoves e essentil fo coect lignment t metphse 1 Spinle fies fom the othe pole ttch to the othe homolog Chismt hol the pi togethe while Tug of w ligns tets Cossoves e nom If two genes e close togethe on the chomosome, they e likely to e inheite togethe. Consequences fo genetic vition Test youself: e vs white fethes own vs white eggs ssume the iniviul is iploi with 3 pis of Is this mitosis o meiosis? Why? Wht stge? Wht kins of gmetes cn it pouce? 3

4 4 Wht is wong with this pictue? gin, ssume the iniviul is iploi with 3 pis of Wht is wong with this pictue? Moe pctice Mitosis o meiosis? Is it coect? Mitosis o meiosis? Is it coect? Even moe pctice

5 Polyploiy Eos in meiosis uplictions of entie genomes Seen in mny plnt species Consequences fo epouctive isoltion x --> How oes meiosis wok in tht tiploi? Steile neuploiy uplictions o eletions of single Eos in meiosis Eos in meiosis: neuploiy Most humn neuplois e ftl. Exception: tisomy 21 (owns Synome) Exception: XXY Tune s synome mles Ntul vition in chomosome nume Species iffe getly in chomosome nume: E. coli: 1 cicul chomosome osophil melnogste: 4 Woo fen: 2N=164 Chimps n goills hve 2N=48 Humns hve 2N=46 How woul tht ffect epouction in pehomini/pe-chimp ncestos? Imgine meiosis n the upliction/eletions tht woul e in the hyi zygotes How woul the hyi (2N=47) mke gmetes? How woul pi? 5

6 vntges of sex: Why sex? voi isese nns e popgte sexully Cvenish viety ccounts fo lmost ll of the commecil nns Pnm isese (Fusium wilt) is speing though si It s peecesso viety, the Gos Michel suffee simil fungl light tht wipe out tht cop in the 1950s isvntges: Nee to fin mte Only pss on hlf of you genes Tht new comintion of genes might e wose... vntges of sex: voi isese on t puchse the sme lottey ticket twice Puge muttions Tht s lot of nns... One solution: ee esistnt vieties Imgine tht two pentl vieties iffe in 15 single genes. To get the esie llele t ech locus, = 1/30,

7 Some ognisms hve oth sexul n sexul stges vntges of sex Puge eleteious muttions Most of them e eleteious Muttions occu evey genetion Ove time, ech chomosome will ccumulte sevel eleteious muttions Without meiosis, the nume of muttions on chomosome will only incese iffeent lineges will cquie iffeent muttions Cossing ove cn pouce some gmetes with fewe muttions