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UNT BIOL 3451 - Meiosis/ Mendelian Genetics
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BIOL 3451 1st Edition Lecture 3 Outline of Last Lecture I. 1.6 Genomics, Proteomics, and Bioinformatics Are New and Expanding FieldsII. 1.7 Genetic Studies Rely on the Use of Model OrganismsIII. 1.8 We Live in the Age of GeneticsIV. Chapter 2: Mitosis and MeiosisV. 2.1 Cell Structure Is Closely Tied to Genetic FunctionVI. 2.2 Chromosomes Exist in Homologous Pairs in Diploid OrganismsVII. 2.3 Mitosis Partitions Chromosomes into Dividing CellsVIII. 2.4 Meiosis Reduces Chromosome # from Diploid to Haploid in Germ Cells and SporesOutline of Current Lecture I. 2.4 Meiosis Reduces the Chromosome # from Diploid to Haploid in Germ Cells and Spores (cont)II. 2.5 The Development of Gametes Varies in Spermatogenesis Compared to OogenesisIII. 2.6 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid OrganismsIV. 2.7 Electron Microscopy Has Revealed the Physical Nature of Mitotic and Meiotic ChromosomesV. Chapter 3: Mendelian GeneticsVI. 3.1 Mendel Used a Model Experimental Approach to Study Patterns of InheritanceVII. 3.2 Monohybrid Cross Reveals How One Trait Is Transmitted from Generation to GenerationVIII. Mendel’s Dihybrid Cross Generated a Unique F2 RatioCurrent LectureI. 2.4 Meiosis Reduces the Chromosome # from Diploid to Haploid in Germ Cells and Spores (cont)- During pachynema, where cross over occurs, remember steps:o 1. Each of two non-sister chromatids is cut using endonuclease (enzyme) at (almost) identical pointsThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.o 2. Exchange of broken chromatid segments between the two non-sister (not connected in same chromosome, but the other chromosome pair in tetrad) chromatids of the same tetrad o To remember: Chromatid: single strand ) Chromosome: 2 strands )( (these 2 are sister chromatids) Tetrad: 2 homologous chromosomes (pairs)/4 chromatids )( )(o 3. The enzyme (ligase) unites the broken chromatid segments with non-sister chromatid of same tetrad (basically: the right hand ends up on the left arm)- Metaphase Io Shortest phaseo Tetrads line up at metaphase plateo Independent assortment: 23 decisions of whether mom or dad’s chromosomes go up or down Therefore use formula to express variation: 2n Put in 23…. 223 Therefore, there is lots of possibilities But, there are also different points where crossover can occur, which just increases genetic variation exponentially. Basically: infinite number of genetic possibilities - Meiosis I: centromeres holding each pair of sister chromatids together do not divide, only the tetrads split and go to opposite poles!o Tetrad: )( )( (2 sister chromosome pairs)o Sister chromatid #1: )( Sister chromatid #2: )(- Meiosis I: 3 ways of genetic variationo Random fertilization (many sperm and many eggs)o Crossing over (*mixes maternal and paternal derived DNA*)o Independent assortment- Point of sexual reproduction is genetic diversity (this is advantageous). Otherwise we each just have our own babies asexually.- Meiosis 2: o Just resolves genetic diversity from Meiosis I No new diversity is introducedo Sister chromatids are separated to opposite poleso Each haploid daughter cell has 1 member of each pair of homologous chromosomeso Same as mitosis, just half of chromosomesII. 2.5 The Development of Gametes Varies in Spermatogenesis Compared to Oogenesis- Spermatogenesis: production of sperm; in the testes, 4 haploid spermatids produced(primary spermatocyte produces 2 secondary spermatocytes, then these undergo Meiosis II, and 4 cells result), goes on for most of male life- Oogenesis: production of eggs in the ovary; daughter cells don’t have equal cytoplasm. Meaning, ovary produces 1 ovum (egg) which undergoes Meiosis I and Meiosis II and 3 polar bodies that are discarded. - Figure 2.12 shows the stages of spermatogenesis and oogenesis. Make note of how the development of each differ. o *secondary spermatocyte: haploid with extra DNAo Spermatids are not the same as spermatozoa; the difference is in developmentIII. 2.6 Meiosis Is Critical to the Successful Sexual Reproduction of All Diploid Organisms- Meiosis necessary for successful sexual reproduction- Gametes receive either maternal or paternal chromosome from each tetrad (homologous pair of chromosomes)- In crossing over, many different points where can occur (called “hot spots”)o Even/odd….50/50: recombination of DNA i.e.: could be every other, every three, every 4…and so on May not be right by each other, but still linked- In some species (like fungi) predominant stage is haploid, not diploid- Multicellular plants: diploid zygote undergoes meiosis to make haploid gametophyteo Alternate between diploid sporophyte(makes spores) stage and haploid gametophyte(makes gametes) stageo Just know what gametophyte and sporophyte are and what they makeo Figure 2.13 As depicted, Meiosis and fertilization bridge the stages togetherIV. 2.7 Electron Microscopy Has Revealed the Physical Nature of Mitotic and Meiotic Chromosomes- Electron microscopy allowed us to view stages of mitosis and meiosis at greater levelso Helps that chromatin fibers of chromosomes coil and condense at this time Figure 2.14 - “beads on a string” idea; wrapped around a nucleosome- 4-5 different levels of coiling of chromatin fibers (2 meters of DNA have to fit in a very tiny space)o Folded-fiber model Figure 2.14cV. Chapter 3: Mendelian Genetics- Mendel modeled the experimental approach while studying inheritance- Had quantitative data!!o First to do this. Others knew that these differences existed, but not the ratios- His work was not recognized as significant during his time, but was later rediscoveredand recognized for his worko His postulates became basis of transmission (genetics)VI. 3.1 Mendel Used a Model Experimental Approach to Study Patterns of Inheritance- Mendel chose garden pea because:o Easy to growo Has true-breeding strainso Has controlled mating; can self-fertilize (has both male and female repo organs) or cross-pollinate (like sexual)- Garden pea Experimento Used 7 visible features, each having 2 contrasting traitso Kept true-breeding strainso Kept quantitative datao Figure 3.1VII. 3.2 Monohybrid Cross Reveals How One Trait Is Transmitted from Generation to Generation- Some definitionso Monohybrid cross: looks at a 1


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UNT BIOL 3451 - Meiosis/ Mendelian Genetics

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