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UNT BIOL 3451 - External Heredity and Chromosome Mutations
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BIOL 3451 1st Edition Lecture 11 Outline of Last Lecture I. 7.5 Dosage Compensation Prevents Excessive Expression of X-linked Genes in Humans and Other MammalsII. 7.6 The Ratio of X Chromosomes to Sets of Autosomes Determines Sex in DrosophilaIII. 7.7 Temperature Variation Controls Sex Determination in ReptilesIV. 8.1 Specific Terminology Describes Variations in Chromosome NumberV. 8.2 Monosomy and Trisomy Result in a Variety of Phenotypic Effects VI. 8.3 Polyploidy, in Which More Than Two Haploid Sets of Chromosomes Are Present, Is Prevalent in PlantsVII. 8.4 Variation Occurs in the Internal Composition and Arrangement of ChromosomesVIII. 8.5 A Deletion is a Missing Region of a ChromosomeOutline of Current Lecture IX. 8.5 Variation Occurs in the Internal Composition and Arrangement of ChromosomesX. 8.6 A Duplication Is a Repeated Segment of the Genetic MaterialXI. 8.7 Inversions Rearrange the Linear Gene SequenceXII. 8.8 Translocations Alter the Location of Chromosomal Segments in the GenomeXIII. 8.9 Fragile Sites in Humans Are Susceptible to Chromosome BreakageXIV. 9.1 Organelle Heredity Involves DNA in Chloroplasts and MitochondriaXV. 9.2 Knowledge of Mitochondrial and Chloroplast DNA Helps Explain Organelle HeredityXVI. 9.3 Mutations in Mitochondrial DNA Cause Human DisordersCurrent LectureI. 8.5 Variation Occurs in the Internal Composition and Arrangement of Chromosomes- Terminal deletion: loss of end of a chromosome because it isn’t attached to a centromere- Formation of a deletion loop- Cri-du-chat: segmental deletion (lost a part of chromosome) “Cry of the cat” scream- *MOST of these chromosome problems are BAD*II. 8.6 A Duplication Is a Repeated Segment of the Genetic Material- Duplications: result of unequal recombination (Figure 8.13) If found to be passed on, then it was helpful for the generations; considered advantageous trait, so allow it to take over May play role in evolutionThese 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.1. Supported by discovery of genes that are commonly found, but their products are distinct2. Presence of gene families: regional groups that perform the same function- Organisms have multiple copies of the ribosomal RNA genes (rRNA) Example of gene redundancy Gene amplification is another mechanism to increase the rRNA1. Go from 1 to many, and keep them all the same- Figure 8.14: Bar-eye phenotype in DrosphilaIII. 8.7 Inversions Rearrange the Linear Gene Sequence- Inversion: rearrangement of linear gene sequence rather than the loss of genetic information May lose gene or two, but not an entire sequence; then, you put it back in somewhere  “Needs of many outweigh needs of the few”= if 1 can survive, then the fact that the other 1000s will die is okay Could result from looping (Figure 8.15) Paracentric inversion: doesn’t change relative lengths of chromosome arms (p and q)1. Dicentric: 2 centromeres2. Acentric: without a centromere Pericentric inversion: includes centromere and does change length of arms Figure 8.16: effects of inversion loop in single crossoverIV. 8.8 Translocations Alter the Location of Chromosomal Segments in the Genome- Translocation: moves from one place to another (usually one chromosome to another) Reciprocal translocation1. Exchange of segments between two nonhomologous chromosomes2. Unusual synapsis configuration during meiosis (with centromere) Two possible patterns1. Adjacent segregation: leads to gametes containing duplications and deficiencies2. Alternate segregation: leads to normal and balanced gamete- Robertsonian translocation: centric fusion breaks at extreme ends of short arms of two nonhomologous acrocentric chromosomes Familial down syndrome is an exampleV. 8.9 Fragile Sites in Humans Are Susceptible to Chromosome Breakage- Fragile sites: more susceptible to chromosome breaking when cells are cultured in absence of certain chemicals like folic acid This is why pregnant women need to eat a lot of folic acid in their diet!!- Fragile-X Syndrome: “Martin=Bell Syndrome” Most common form of inherited (chromosome based) mental retardation Considered dominant Fragile site at FMR-1 of CGG sequence Normal individual: CGG repeats anywhere from 6-54 times Fragile X syndrome: CGG repeats more than 230 times- Found fragile site related to lung cancerVI. 9.1 Organelle Heredity Involves DNA in Chloroplasts and Mitochondria- Extranuclear influences phenotype Maternal DNA (mitochondria/chloroplasts)- Three types of heredity: Organelle heredity: a variety of extranuclear inheritance, DNA is (LOOK AT) In factious heredity: results from symbiotic or parasitic association with microorganism Maternal effect on phenotype, gene products used in zygotes are stored in egg(come from what mom put in there)1. Distributed to cells of developing embryo and influence phenotype - Inheritance of mitochondrial/chloroplast traits often determined by phenotype of ovule source- Analysis of inheritance patterns resulting from mutant alleles has been difficult because: Organelles contribute to progeny of cell and there is a lot of variation: you just split cell and there will be some mitochondria here (heteroplasmy: 2 different mitochondrial nuclei), and some on the other. Therefore, more complicated than Mendelian genetics Function of organelles depend on gene products from nucleus and organelle, making origin of mutations affecting organelle function difficult- Chlamydomonas: good model for studying organelle heredity because has a single chloroplast that shows uniparental inheritance Ruth Sager (1954) show differences in reciprocal crosses with strains of strep virus, trait passed on through female parent- Mitochondria also have a diverse genetic system (like chloroplasts), where mutations are transmitted through the cytoplasm (Mitchell and Mitchell, 1952) S. cerevisae show that small percent of these mutations are nuclear in nature and called: segregational petites Neutral petites: mitochondria are inherited from both parental cells and replicated in offspring Suppressive mutation: may not be observed initially in offspring but becomes apparent after period of time Figure 9.5VII. 9.2 Knowledge of Mitochondrial and Chloroplast DNA Helps Explain Organelle Heredity- Endosymbiotic theory:


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UNT BIOL 3451 - External Heredity and Chromosome Mutations

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