Mitosis & Meiosis- Information Management in Cell Division7I. Separation of DNA copies during cell division to produce exact copiesA. Prokaryotes1. simple -generally single copy of DNA, separates copies with separating cellsB. Eukaryotes- Mitosis1. complicated by division of genome into chromosomes as piecesKARYOTYPE: the set of chromosomes as seen during cell divisionIdentified by CENTROMERE location and BANDING PATTERNS2. complicated due to copies of chromosomesHOMOLOGOUS CHROMOSOMES: have same/similar genes but different originHAPLOID: number of unique chromosomes = nDIPLOID: 2n chromosomesSISTER CHROMATIDS: Exact copies made from DNA synthesis3. Mitosis - Part of CELL CYCLEInterphase: G1 (G0-rest), S (DNA synthesis to make sister chromatids), G2-checkpoints in cell cycle determine progressMITOSIS: M phaseProphase. Chromosomes condense, Spindle microtubulesPrometaphase. Microtubules attach to centromere at a kinetochoreMetaphase. Chromosomes align, each sister attached to opposite centrosomesAnaphase. Separation of sister chromatids due to kinetochores anddisassembly of microtubles at ends-sister chromatids held together by cohesion protein until digested by separase just before anaphaseTelophase chromosomes reach ends and decondenseCytokinesis. Separation into separate cells4. Variation in mitosis- skipping cytokinesis can produce multinucleate cell orskipping M phase altogether or anaphase gives >2n nucleus5. Mistake in mitosis- leads to formation of mosaic organism- differences between cellsII-Chromosome separation during gamete formation-MEIOSISA. Purpose is to create haploid gametes, so needs to separate homologous chromosomes-creates diversity in progenyB Stages: Starts in cell cycle like mitosis, so sister chromatids are formed in S phase1. Meiosis I- separates homologous chromosomesProphase I- important since formsSYNAPTONEMAL COMPLEX- physical pairing of homologous chromosomesCHIASMATA-exchange of strands of sister chromatids from separate homologous chromosomesCrossing over of homologous chromosomes-sisters are no longer exact copies2. Interkinesis3. Meiosis II- separates “sister” chromatidsC. Genetic diversity among gametes created by:1. Independent assortment of homologous chromosomes2. Crossing over on homologous chromosomes mean sister chromatids are not exact copiesD. Mechanism in choreography of mitosis/ meiosis-proteins which attach chromosomes- Cohesin, separase digests cohesin,Shugoshin protects cohesin at centromeres of sister chromatids in meiosis IE. Mistakes in Meiosis-1. Nondisjunction in anaphase I or II- produces gametes n+1 and n-12. Parthenogenesis-reproduction without male- can result from failure or reversal of meiosis somakes 2N cell from egg aloneI. Prior ideas for genetic inheritance-Preformism, Pangenesis, Blending InheritanceII. Gregor Mendel Mendelian Genetics- 1860's Sweet pea hybridization-applied mathematical analysis- frequencies of trait segregation in crosses-predicted existence of traits encoded in units (gemules vs genes)Terminology:Gene: a basic unit of biological information, encodes a protein or RNAAlleles: alternative forms of a single geneLocus: a designated location on a chromosome (e.g. a gene)Genotype: the actual genetic makeup of an individual-e.g. sequence variation at a genePhenotype: a observable characteristic or trait due to a variation in functionHeterozygous:A genotype in which the two copies of the gene that determine a particular trait are different allelesHomozygote: A genotype in which the two copies of the gene that determine a particular trait are the same alleleReciprocal crosses: Crosses in which the phenotypes of the male and female parents are reversedIII. Monohybrid cross - cross involving a single traitA. Round seed = RR X wrinkled seed = rr-R allele encodes round allele-r allele encodes wrinkled allele- parents are homozygous (true bred) PUNNETT Squarealleles in each haploid gamete – male rr parentrrRRrRrPossibleRRrRrcombinationsalleles in eachhaploid gamete – RR female parent Rr= round phenotype-all progeny are heterozygous: Rr-all are round phenotype-round allele is dominant: RR and Rr are both round-wrinkled allele is recessive: only wrinkled when rrdominant - the trait that appears in the heterozygous conditionrecessive - the trait that is masked in the heterozygous conditionB. Next generation:1. cross progeny round Rr X round Rr-crossing heterozygotesRrRRRRrrRrrr1 RR=round genotypic ratio 1:2:12 Rr = round phenotypic ratio 3:11 rr=wrinkled2. Results:-each unit of heredity comes in two alternate forms (alleles)- don’t mix-each individual had two units-homologous chromosomesC. Mendel’s Law of Segregation-Unit of inheritance exists in two forms (alleles)when an individual produces gametes, they separate them so that a gamete gets only one from each parentD. Test CrossesMeans of testing the genotype of an unknown individual with a dominant phenotype.-cross unknown dominant with a known recessive (truebred so known homozygous)R? x rr if get 4/4 Round (dominant) then R/? was RRIf get 2/4 wrinkled (recessive) then R/? was RrIV. Dihybrid cross - cross involving two traitsA. if on two separate chromosomes- traits segregate independently- eg. seed coat gene: round allele = R, wrinkled allele = rseed color gene: Yellow allele = Y, green allele = y- parents: Round green seed: RR/yyWrinkled yellow seed: rr/YY-first generation: all are Rr/Yy heterozygous-all are round and yellow- these are dominant allelesB. second generation-Rr/Yy x Rr/Yy classic “dihybrid cross”-progeny display9 different genotypes (RR/YY, RR/Yy, Rr/YY, Rr/YY etc.)4 different phenotypes: out of 16,- 9 are like parents: round and yellow- 3 are like one grandparent: wrinkled and yellow- 3 are like the other grandparent: round and green-1 is unlike parent or grandparents: wrinkled and green- 9 : 3 : 3 : 1 ratioC. Result:-independent assortment of each trait- as if each unit is separate (i.e. chromosomes)-produces a reassortment of traits so each progeny represents a novel combination of traits from both parentsD. Mendel’s Law of independent assortment-During gamete formation, different pairs of alleles for separate traits segregate independently of each otherV. Using probability rather than Punnett squaresA. The Multiplication Rulethe probability of two or more independent events occurring together is calculated by multiplying their independent probabilitiese.g. dihybrid crosses multiply fractions segregating at each