CYTOGENETICS AGR 6353
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This 3 page Class Notes was uploaded by Elaina Gorczany on Friday September 18, 2015. The Class Notes belongs to AGR 6353 at University of Florida taught by Kenneth Quesenberry in Fall. Since its upload, it has received 16 views. For similar materials see /class/206615/agr-6353-university-of-florida in Agricultural & Resource Econ at University of Florida.
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Date Created: 09/18/15
XII 2n Gametes AGR 6353 Cytogenetics Fall 2007 K H Quesenberry A Introduction 1 First reported by Gates 1909 in Oenothera 2 Two basic types of Zn gamete formation a First Division Restitution FDR Incomplete 1st meiotic division FDR 2ngametes comprise the nonsister chromatids of each homologous pair of chromosomes and are genetically identical to parent b Second Div ion Restit on SDR Incomplete 2nd meiotic diVIsion SDR 2n ametes include the sister chromatids Spores are completely homozygous but genetically different B Schematic representation comparing meiosis in cells with normal and parallel orientation of second 39 I n spindles Propnasel gt lnterpnasel Parallel Spindles Normal 3332233 Meiotic Q Products A M 2 In a normal meiosis the Al spindle fiber orientation is quotperpendicularquot to the All spindle fiber orientation 3 thn parallel spindles both Aland All spindles are in the same direction zen spines 17 2n spare C Comparison of results from normal meiosis incomplete first FDR orincomplete second d on restitution SDR ofmeiosls l i I x H i i i 1 2 39 gt gt I 2 2 2 2 2 2 2 M A M II Tetrad Normal Meiosis C Comparison of results from normal meiosis incomplete first FDR or incomplete second diVIsion restitution SDR sis 2 of melo 1 H l 1 11 2 39 a n 2 2 W H 22 M A M II Dyad Incomplete First Division quotFirst Division Restitutionquot C Comparison of results from normal meiosis incomplete first FDR orincomplete second diVIsion restitution SDR 39 sis 3 of melo 1 II 1 1 11 12 2 2 l1 2 V 22 Ml Al Mll Dyad Incomplete Second Division quotSecond Division Restitutionquot D Genetic Consequences of FDR Assuming One Crossover per Pair of Homologous Chromosomes 1 A jAHa Aa a A a a AHE aHA Crossover between locus and centromere 50 horn 01 50 heteroz D Genetic Consequences of FDR Assuming One Crossover per Pair of Homologous Chromosomes 2 BuB E 3 4 be b No crossoverbetween locus and centromere 100 Heterozygous also all genes on short arm 3b Bb represents all heterozygous loci affected by the crossover those not affected by the crossover E Genetic Consequences of SDR Assuming One Crossover per Pair of Homologous Chromosomes 1 AHa la a ilt AHa Aa Aa unlgtgt Crossover between AH a locus and centromere a A 100 Heterozygosity E Genetic Consequences of SDR Assuming One Crossover per Pair of Homologous Chromosomes 2 B a B B B B 2 I B b I L a b b b b b No crossover between locus and centromere 0 oHomozygous 55 bb also all genes on short arm represents all heterozygous loci affected by the crossover those not affected by the crossover F Summary FDR vs SDR Gametes 1 1 First Division Restitution a Transfer average of 80 of parental heterozygosity to progeny b Therefore heterozygous parents produce heterogametes w ich lead to multiallelic loci and high vigor in autotetraploid progeny c Gametes are largely genetically to parent and thus progeny are very uniform F Summary FDR vs SDR Gametes 2 2 Second a Have a relatively high level of homozygosity maybe up to 80 from parent which is 50 homozygous This may increase dosage of alleles for certain desirable simply inherited dominant characters c Gametes from heterozygous parent are heterogeneous Therefore progeny are heterogeneous and potential for progeny selection increases Equot w Semiheterotypic d39 G General Mechanism of Zn Gamete Formation 1 Premeiotic doubling with autobivalent formatio n Allium Chromo ouble in early prophase and sister chromatids stick together Homologs do not pair FDR Mitotized meiosis d n of chromosomes in EMC similar to mitosis 2n megaspores Ex Poa spp n chromosomes of EMC hardly or do not pair Univa ents at Ml are irregularly distributed Followed by 2nd division resulting in 2n amete G General Mechanism of Zn Gamete Formation 2 4 Pseudohomotypic div n chromosomes of EMC do Io not pair Univalents dIVIde equationally at Ml Gametes are to FDR 2n gametes Ex Solanum 5 Synaptic mutants interspecific hybrid etc 6 Genetic control pc1 and pc 2 SDR potato ps potato rp alfalfa FDR pc premature cytokynesis ps parallel spindles rp round poHenL
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