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1 of 2 Genetics Res: on Chromosomes: NOTES 2 Jan 6, 2014 Dr. Nedwidek Stuyvesant HS Aim: How are genes and chromosomes structured in Eukaryotes? Human genes have some very different and important structural features. Draw the key features of a human (mammalian eukaryotic) gene (based on Thompson genetics, page 20) and a bacterial gene (based on Griffiths 354 and your class notes) in your notebooks. *1 drawing Use Ch 16 Griff to review chromosome structure. Know major differences between prokaryotic and eukaryotic chromosome organization. Know that prokaryotic genomic DNAs are circular with no nucleus and no protein scaffolding present. Eukaryotic genomes are larger, more complex, and more organized. Know that Downs (47), Turners (45), and Klinefelters (47) have in common that they are all caused by nondisjunction (NDJ) events; the numbers next to each condition refer to what? Important terms you need to and should know but I do not have time to redefine because they should be hardwired by now are haploid, diploid, nucleosome, chromatin, histone, centromere, telomere, homologues, chromatids. Bacterial genomes = 4.6 Mb = 4.6 x 10^6 bp Human genome = 3.1 x 10^9 bp Genome sizes Griff 454/ bacterial stats on 760 Human Genome project: Initial guess was 100,000 genes. Actual was found to be less than 30,000 genes (close to 25,000 genes). Mutations at the level of chromosomes can cause genetic disease, so knowing how they are put together is important. Turners, downs and Klinefelter’s all result from aberrations in chromosome number. Draw the anatomy of a chromosome post-replication from the board. *2 drawing During mitosis and meiosis, copying and division accomplish recruitment and safe redistribution of the genome. Mitosis forms two identical somatic cells. Meiosis does not generate identical outcomes; it accomplishes shuffling and distribution of genomes to the germline. Outline the key events of meiosis with a crossover event. *3 drawing General ploidy relationships in NDJ: It is unlikely that one defective haploid complement would make up for another, but these events happen in pairs. For 2n=4 (dip), n=2 (hap) Complementary, connected Norm norm Male, sperm hap n n Norm norm Female, egg hap n n Diploid 2n 2n Total Chromosomes 4 4 complementary, connected events abnorm abnorm n+1 n-1 norm norm n n 2n+1 2n-1 5 3 2 of 2 Meiotic nondisjunction event outcomes in humans Klinefelters: XX egg + Y sperm most likely Downs: (#21, #21) egg + (#21) sperm or the converse Turners: (No X) egg + (X) sperm or converse (X) egg + (no X) sperm Supermale: (X) egg + (YY) sperm only Aim: How do we describe all the things that can go wrong with whole chromosomes? Terms to know: Euploidy: Plants: certain chromosome set (complete) but X-fold: triploid (3), tetraploid (4), pentaploid (5), hexaploid (6). Refers to whole genome. Monoploidy: not sex cells; insects and plants; not haploid (n). Polyploidy: prevalent and normal in plants because of tissue specialization (ex is triploid endosperm in fruits) Autopolyploidy (plants): polyploidy from doubling of one genome of species (whole organism) Allopolyploidy: chromosome sets from two different species unite and double (ex: mule). Endopolyploidy: polyploidy in certain cells only: examples, vertebrate liver and insect gut. Polyteny: in insects. Multicopies of DNA within a haploid chromosome set. Aneuploidy: difference from normal in small number of chromosomes within the set. Nondisjunction event is responsible. Aneuploids can be: Post-fert, abnormal diplod variations: trisomic (2n+1) Monosomic (2n-1) Nullisomic (2n-2) Pre-fert, abnormal haploid variations: disomic (n+1) Examples of disorders that are due to aneuploidy are turners (monosomy); Klinefelters (XXY), downs (+21), XYY, XXX, Edwards (+18), Patau (+13)- (all trisomies) **Aneuploidy is always bad in humans. Ploidy affects gene balance, which affects dosage, or the number of available, expressed DNA templates. Dosage compensation in humans: the X chromosome is altered or suppressed in females. Defects in ploidy affect dosage (ex turners females). Next…Phenotypes for chromosome damage…look at griff 572.