BIOL 120 1st editionExam # 4 Study GuideMeiosis- Key Concepts o is a type of reduction division  leads to formation of eggs and sperm (gametogenesis) o each cell produced by meiosis receives different gene combinations on chromosomes o Offspring are genetically distinct NOT identical cellso 4 daughter cells are formed with 23 chromosomes in each o Meiosis is nuclear division that comes before the formation of gametes  halving of chromosome numbero Meiosis reduces chromosome number by half  diploid to haploid - Consist of two cell divisions: Meiosis I and Meiosis II o Meiosis I  diploid parent cell produces two daughter cells homologs in each chromosomes pair separate and go to different daughter cell  haploid daughter cells still have chromosome of two identical sister chromatid - No replication after Meiosis I o Meiosis II  sister chromatid of each chromosome separate and go to different daughter cells  similar to mitosis  produces 4 haploid daughter cells  called gametes through the process of gametogenesis - Fertilization of gameteso Results in a zygote  fertilized cells containing a full complement of chromosomes (diploid)  Receives a haploid from each parent - Meiosis Division o Interphase  DNA replicationo Meiosis I  separation of homologous chromosomes  Prophase I Metaphase I Anaphase I Telophase Io Meiosis II Prophase II Metaphase II Anaphase II Telophase IIo Cytokinesis o Results in: four gametes with a chromosome composition different from parent cells Sexual reproduction creates great genetic variety  Separation and distribution of homologous chromosomes during meiosis I creates variety  giving each daughter cell a great deal of genetic diversity - Crossing Overo Occurs in Prophase 1 results in recombinant chromosomes o At the point where chromosomes cross over the non-sister chromatid from each homolog physically break at the same point and attach to each other  maternal and paternal chromosomes are swapped- Mendel’s Experimento 19th century monk interested in heredityo Understood that all traits have 2 possible alleles (1 from mom and one from dad) Homozygous  matching alleles (RR or rr) Heterozygous  different alleles (Rr)o Used garden peas for his experiment  controlled pollination by preventing self-pollinationo Studied: seed shape, seed color, pod shape, pod color, flower color, flower and pod position, and stem length  Focused on Phenotype  observable features Used pure-lines  identical offspring from self-pollinationo Dominate alleles always show over recessive - Monohybrid crossingo Studies only 2 variations of a single trait o F1 generation  the offspring produced from 3 true breed strains  Only shows dominate traitso F2 generation  offspring of F1 Result from self-fertilization of F1 plants  Recessive traits begin to reappear in F2  Phenotypic ratio  3 dominant: 1 recessive Genotypic ratio  1 homozygous dominant: 2 heterozygous dominant: 1 homozygous recessive o Genotype: allelic make up of an individualo Phenotype: physical manifestation of genotype in an environment - Punnett Squareso A method used to determine possible genotypes o Example of F2 generation:o- Dihybrid Crossingo Examination of 2 separate traits in a single cross event o F1 generation still shows only dominant phenotypes o F2 generation ratio  9 dominant, dominant: 3 dominant, recessive, 3 recessive, dominant: 1 recessive, recessive- Test crosso a cross used to determine the genotype of an individual with dominant phenotype o you cross the individual with an unknown genotype (P_) with a homozygous recessive (pp) in order to solve the unknown - Incomplete Dominance o heterozygote is intermediate in phenotype between 2 homozygotes i.e. a red and a white flower produce a pink flower - Codominanceo heterozygote shows some aspects of the phenotype of both homozygotes i.e. blood typeAB (A and B are both dominant so being together makes them both appear in phenotype)o human blood groups  has 3 alleles Type A blood  A is dominant Type B blood  B is dominant Type AB  A and B are codominant (universal receiver) Type O blood  has no dominant (universal donor) - Epistasiso The behavior of gene production can change the ratio expected in independent assortment  not 3:1 - Polygenic Inheritanceo occurs because multiple genes are involved in controlling the phenotype of a trait  phenotype is a buildup of multiple geneso traits show continuous variation (known as quantitative traits) i.e. human height - Pleiotropyo is an allele that has more than one effect on the phenotype (cystic fibrosis)Genetic Material - Frederick Griffith studied strands of pneumonia o S strain  caused pneumoniao R strain  did not cause disease o infected mice with these strains  live S strain killed the mice and live R strain did not heated S strand did not kill the mice (virus was killed by heating)- combination of live R strain and heated S strain killed the mice (Combination allowed DNA of heated S strain to recover in the live R strain) - known as transformation- Review of DNAo Nucleic acido Composed of: 5 carbon sugar Phosphate group (attached to 5’ carbon) Nitrogenous base (Adenine, thymine, cytosine, guanine)o Strands grow in 5’ to 3’ direction o Chargaff’s rule  equal proportions of Purines (A and G) and Pyrimidines (C and T)- amount of adenine = amount of thymine- amount of cytosine = amount of guanine o DNA is a double helix  A forms 2 hydrogen bonds with T C forms 3 hydrogen bonds with Go DNA has a diameter of 2nmo Complete turn of helix occurs ever 3.4 nmDNA Replication - Occurs in interphase- DNA copies are semiconservative (part of the old strand bonded with new strand)- Semiconservative theory proven by Meselson and Stahl (1958)o grew cells in N15 and N14o DNA was extracted at different time intervals to view replicationo N15 is heavier than N14  location of N15 DNA was lower than N14 DNA and the semiconservative strand of N14 and N15 was in the middle proving it true- Requireso Paternal DNA to copy (and primer)o Enzymes to copy DNAo NTPs (building blocks to make copy of DNA)- Processo Initiationo Elongationo Termination - Process is Semi- discontinuous o Leading strand (5’ 3’) synthesized continuously o Lagging Strand (3’  5’) synthesized discontinuously with multiple