Mitosis Meiosis 02 26 2014 Mitosis Meiosis Information Management in Cell Division 7I Separation of DNA copies during cell division to produce exact copies A Prokaryotes B Eukaryotes Mitosis 1 simple generally single copy of DNA separates copies with separating cells 1 complicated by division of genome into chromosomes as pieces KARYOTYPE the set of chromosomes as seen during cell division Identified by CENTROMERE location and BANDING PATTERNS 2 complicated due to copies of chromosomes HOMOLOGOUS CHROMOSOMES have same similar genes but different origin HAPLOID number of unique chromosomes n DIPLOID 2n chromosomes SISTER CHROMATIDS Exact copies made from DNA synthesis 3 Mitosis Part of CELL CYCLE Interphase G1 G0 rest S DNA synthesis to make sister chromatids G2 checkpoints in cell cycle determine progress MITOSIS M phase Prophase Chromosomes condense Spindle microtubules Prometaphase Microtubules attach to centromere at a kinetochore Metaphase Chromosomes align each sister attached to opposite centrosomes Anaphase Separation of sister chromatids due to kinetochores and disassembly of microtubles at ends sister chromatids held together by cohesion protein until digested by separase just before anaphase Telophase chromosomes reach ends and decondense Cytokinesis Separation into separate cells 4 Variation in mitosis skipping cytokinesis can produce multinucleate cell or skipping M phase altogether or anaphase gives 2n nucleus 5 Mistake in mitosis leads to formation of mosaic organism differences between cells II Chromosome separation during gamete formation MEIOSIS A Purpose is to create haploid gametes so needs to separate homologous chromosomes creates diversity in progeny B Stages Starts in cell cycle like mitosis so sister chromatids are formed in S phase 1 Meiosis I separates homologous chromosomes Prophase I important since forms SYNAPTONEMAL COMPLEX physical pairing of homologous chromosomes CHIASMATA exchange of strands of sister chromatids from separate homologous chromosomes Crossing over of homologous chromosomes sisters are no longer exact copies 2 Interkinesis 3 Meiosis II separates sister chromatids C Genetic diversity among gametes created by 1 Independent assortment of homologous chromosomes 2 Crossing over on homologous chromosomes mean sister chromatids are not exact copies D Mechanism in choreography of mitosis meiosis proteins which attach chromosomes Cohesin separase digests cohesin Shugoshin protects cohesin at centromeres of sister chromatids in meiosis I E Mistakes in Meiosis 1 Nondisjunction in anaphase I or II produces gametes n 1 and n 1 2 Parthenogenesis reproduction without male can result from failure or reversal of meiosis so makes 2N cell from egg alone Mendelian Genetics Patterns of Information Inheritance 02 26 2014 I Prior ideas for genetic inheritance Preformism Pangenesis Blending Inheritance II 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 RNA Alleles alternative forms of a single gene Locus a designated location on a chromosome e g a gene Genotype the actual genetic makeup of an individual e g sequence variation at a gene Phenotype a observable characteristic or trait due to a variation in function Heterozygous A genotype in which the two copies of the gene that determine a particular trait are different alleles Homozygote A genotype in which the two copies of the gene that determine a particular trait are the same allele Reciprocal crosses Crosses in which the phenotypes of the male and female parents are reversed III Monohybrid cross cross involving a single trait A Round seed RR X wrinkled seed rr R allele encodes round allele r allele encodes wrinkled allele parents are homozygous true bred PUNNETT Square alleles in each haploid gamete male rr parent r Rr Rr r Rr Rr Possible combinations R R alleles in each haploid 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 rr dominant the trait that appears in the heterozygous condition recessive the trait that is masked in the heterozygous condition B Next generation 1 cross progeny round Rr X round Rr crossing heterozygotes R RR Rr r Rr rr R r 1 2 1 3 1 1 RR round genotypic ratio 2 Rr round phenotypic ratio 2 Results 1 rr wrinkled each unit of heredity comes in two alternate forms alleles don t mix each individual had two units homologous chromosomes C Mendel s Law of Segregation Unit of inheritance exists in two forms alleles each parent D Test Crosses when an individual produces gametes they separate them so that a gamete gets only one from Means 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 RR If get 2 4 wrinkled recessive then R was Rr IV Dihybrid cross cross involving two traits A if on two separate chromosomes traits segregate independently eg seed coat gene round allele R wrinkled allele r seed color gene Yellow allele Y green allele y parents Round green seed RR yy Wrinkled yellow seed rr YY first generation all are Rr Yy heterozygous all are round and yellow these are dominant alleles B second generation Rr Yy x Rr Yy classic dihybrid cross progeny display 9 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 ratio 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 D Mendel s Law of independent assortment During gamete formation different pairs of alleles for separate traits segregate independently of V Using probability rather than Punnett squares A The Multiplication Rule the probability of two or more independent events occurring together is calculated by multiplying their independent C Result both parents each other probabilities e g dihybrid crosses multiply fractions segregating at each gene B The Addition Rule the