BIOL 120 1st edition Exam 4 Study Guide Meiosis 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 cells o 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 number o 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 gametes o Results in a zygote fertilized cells containing a full complement of chromosomes diploid Receives a haploid from each parent Meiosis Division o Interphase DNA replication o Meiosis I separation of homologous chromosomes Prophase I Metaphase I Anaphase I Telophase I o Meiosis II Prophase II Metaphase II Anaphase II Telophase II o 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 Over o 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 Experiment o 19th century monk interested in heredity o 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 selfpollination o 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 pollination o Dominate alleles always show over recessive Monohybrid crossing o Studies only 2 variations of a single trait o F1 generation the offspring produced from 3 true breed strains Only shows dominate traits o 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 individual o Phenotype physical manifestation of genotype in an environment Punnett Squares o A method used to determine possible genotypes o Example of F2 generation o Dihybrid Crossing o 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 cross o 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 Codominance o heterozygote shows some aspects of the phenotype of both homozygotes i e blood type AB 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 Epistasis o The behavior of gene production can change the ratio expected in independent assortment not 3 1 Polygenic Inheritance o occurs because multiple genes are involved in controlling the phenotype of a trait phenotype is a buildup of multiple genes o traits show continuous variation known as quantitative traits i e human height Pleiotropy o 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 pneumonia o 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 DNA o Nucleic acid o 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 G o DNA has a diameter of 2nm o Complete turn of helix occurs ever 3 4 nm DNA 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 N14 o DNA was extracted at different time intervals to view replication o 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 Requires o Paternal DNA to copy and primer o Enzymes to copy DNA o NTPs building blocks to make copy of DNA Process o Initiation o Elongation o Termination Process is Semi discontinuous o Leading strand 5 3 synthesized continuously o Lagging Strand 3 5 synthesized discontinuously with multiple priming events copies in short fragments Okazaki Fragments Eukaryotic DNA Replication o Uses multiple replicons multiple origins of replication of each chromosome to make process faster o main replication polymerase DNA polymerase epsilon and DNA polymerase delta o Telomeres They are specialized structures found on the ends of eukaryotic chromosomes to protect ends from nucleases and