BGYB10&B11 Midterm 2 Study Guide

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University of Toronto Scarborough
Biological Sciences
Mary Olaveson

BGY10 J Midterm #2 Lecture #1: Chromosomes, Genes, DNA J Chapter 10 - units of inheritance govern plant characteristics (genes encoded by DNA) - each plant has 2 copies of gene J alleles = control trait development (homo/hetero-zygous) - inheritance = allele comes from each parent - traits can be either dominant or recessive - gametes = reproductive cells, have only 1 copy of each gene/trait - each pair of alleles = genotype which produces trait = phenotype J remain together thru life but can be separates/segregated during reproduction (gamete/meiosis formation) - Z22]}L}]}oooZ}ZL[ }ZoooZ o Law of Segregation9}2L]ZKZ[oooZZlZ22]L2 gamete formation J 1 gamete carries 1 allele for each trait o Law of Independent Assortment: segregation of allele pair for 1 trait has no effect on segregation of alleles for another trait (segregate independently) - chromosomes = carry inheritable traits (genes) J each interphase chromosome has 1 double- stranded DNA molecule w/ many genes - eukaryotic nuclear chromosomes are linear, prokaryotic chromosomes are circular - 1880s, Flemming observed concept that material outside nucleus becomes organized into visible threads (chromosomes) during cell division - 1903, Sutton used sperm cells (spermatogonium) of grasshopper for homologous chromosomes o pairing of homologous chromosomes = tetrads/bivalents st o 1 meiotic division separates 2 homologous chromosomes into different cells o mitosis separates 2 chromosomes into 2 cells - homologous chromosomes ~l,Lo[Z]LZ]o]ZZ}ZZ]Z9 Z}K}Z}KZ physical carriers of genetic factors (and meiosis is a reductive division) - mutations = spontaneous inheritable changes in genesoccur o can b induced by chemicals that damage DNA o include substitutions, deletions, insertions, inversions J can lead to change in gene expression - altered trait passed thru generations if mutation occurs in germ-line cells = gametes but if in somatic cells, not inheritable - mutations result in variation in pops J different pops can become genetically different = evolutionary role - mutations (spontaneous or induced) used for genetic studies J comparing wild type to mutants - 2 different genes on same chr}K}Z}K}L[oZK]L}2Z]L22K production (not linked) - crossing over/recombination causes genes on separate homologous chromosomes to shuffle o result: in maternal and paternal genes inherited on same chromosome, breakdown of linkage as result of bivalents exchanging genetic material during meiosis - during meiosis, cross over points occur at recombination nodules J chiasma forms at point where crossing over has occurred o single cross over even on one homologous chromosome pair - recombination frequency at loci (gene position on chromosome) determined by distance between 2 genes on chromosomes o greater distance between 2 genes on chromosomes = more likely to cross over (breakage J genes become unlinked) o can be used to map gene positions on chromosomes - meiosis = reductive process J produced haploid gametes by 2 sequential divisions w/out DNA replication o in prophase I, crossing over occurs J genetic diversity - synaptonemal complex (Sc): chromosome synapsis accompanied by formation of SC J Sc believed to provide scaffold for chromatids to complete crossing over and is fully formed in pachytene o recombination nodule form w/in SC and correspond to crossing over events o at completion of crossing over, SC breaks down = end of prophase I o lateral elements bind together chromatin of sister chromatids J protein filaments connect that 2 lateral elements of SC - in meiosis I, metaphaseI J homologous pairs held together as bivalent by chiasmata: forms after SC dissolves and cohesions holds chromatids together too o in anaphase I, cleavage of cohesions allow separation of homologues o in meiosis II, metaphase II J cohesion at centromere and separation of homologous chromosomes during meiosis I and separations of chromatids in meiosis II o in anaphase II J kinetochore formed, cohesion at centromere cleaved and chromatids move to opposite poles - DNA = deoxyribonucleic acid, double stranded (2 strands of DNA), w/ double helix and 4 different nucleotides - nucleosides = just a sugar and a base - nucleotides = a nucleoside w/ 1, 2, or 3 phosphates J A and G = purines (2 rings, bigger), C and T = pyrimidines (1 ring, smaller) - DNA = linear J info in specific order, each strand used as template for DNA replication J is unbranched, made of monomeric subunits (4 nucleotides = dATP, dCTP, dGTP, dTTP), and antiparallel = complementary - strands held together by H bonds J weak individually and easily broken o long chain of nucleotides = stable b/c of H bonds o ability to break bonds allow DNA stands to denature and renature (for DNA rep and RNA syn J transcription) - Z2[ZZ]L2: A=T, G=C, but A+T does not = G+C - DNA double stranded molecule in spiral to form pair of right-hand helices (J}K o 2 chains comprise of 1 double helix J run in opposite directions - DNA has sugar/phosphate backbone on outside of molecule w/ base from each strand in center J 2 bonds between A+T and 3 bonds between G+C o major/minor grooves of double stranded molecule = site of transcription factor binding sites - Watson and Crick bp: structural restriction of base interactions, entire DNA strand complementary to other strand, and complementarity critical to all nucleic acid interactions - genome = entire DNA makeup of organism - eukaryotes: nuclear, extra chromosomal (outside nucleus J e.g. chloroplast, mitochondria)), mitochondria, chloroplast, plastid - genetic material used for: storage, DNA template (replication J cell division, inheritable J daughter cells), gene expression - supercoiling = DNA molecule twists on itself o when DNA unwound and not supercoiled, unstable o ZoJ-form, right handed helix, 10 bases/turn, considered underwound = negative supercoils o positive supercoils = left-handed helix, considered overwound o relaxed = no supercoils in most of circle J more than 10 bases/turn b/c of nicking o stressed/positive supercoils = Topoisomerases alter DNA supercoiling for DNA rep and transcription by nicking 1 strand (Topo I) and allow separation of sister chromatids by double-stranded break (Topo II) J Topoisomerase used to relax double stranded DNA when the strands separate (an enzyme) Lecture #2: DNA J Chapter 10 - double helix so 2 strands can unwind (held together by H bonds J weak and noncovalent) and separate into 2 individual strands = denaturation - when DNA dissolved in weak saline solution and slowlywarmed to certain tem, strands begin to separate and few degrees more, strand completely separated J driven apart by electrostatic repulsion of negative charges on sugar-phosphate backbone - DNA melting (denaturation) monitored by following increase in absorbance of dissolved DNA - *nitrogenous bases of nucleic acids absorb UV radiation at absorbance maximum near 260nm* - single stranded DNA absorbs twice as much light J can use absorbance to monitor de/re- naturation - Ko]L2K)KZZZ]]LZ}L ]ZZo }Ko - ability of complementary single strand to reassociate = reanneal (follows denaturation into stable double-stranded molecule) critical for moleculeprocess and important bio observation - nucleic hybridization = complementary strands from different sources mix to form double- stranded hybrid molecule J base for genome complexity - 3 steps in renaturation: highly repeated fraction, moderately repeated fraction, nonrepeated fraction o highly repeated fraction = clusters in tandem, anneal quickly, need dilute concentrations to monitor o moderately repeated fraction = 20-80% of DNA, can code for RNA/proteins o nonrepeated fraction = single copy, most proteins, multigene families - simple-sequence DNA composed of tandem repeats of short sequences = short tandem repeats (STR) from gene duplication o 1. satellite DNA (5-500bp) in tandem repeats up to 100Kb J found at centromeres and telomeres o 2. microsatellite (1-5bp) clustered 50-100bp, scattered in genome, highly variable (mutations) used to compare pops o 3. minisatellite (12-100np) up to 3000 repeats (1-5kB) variable (polymorphic), differ in individuals of pops, criminal and paternity cases (DNA fingerprinting/RFLP) using Southern blotting/PCR - DNA hybridization = ability of DNA to reanneal J can be used to map relative location of single copy of genes - Southern Blot = nucleic acid hybridization J detect DNA complementary to probe - DNA = genetic material o sequence organization in genome can change rapidly from 1 generation to
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