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ARCH131 Unit 3

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Simon Fraser University
ARCH 131
Dennis Sandgathe

UNIT 3: Genetics Week 2 3.1 Inheritance and Mendel's Principles • The Mechanisms of Inheritance of Traits; • 19 Century views of Inheritance: Blending of traits • Breeding or artificial selection ie. Corn varieties/AUROCHS > Heckrind: recreated version of the extinct species > slightly smaller/less violent Gregor Mendel (1822-1884): 1850s Research on Plant Hybridization − Mendel's Pea Plant Traits (had 7 characteristics): he crossed pea plants that contrasted each other What Mendel saw: Generation 1 (parents): s+w offspring: (generation 2) s s s s Generation 2: s + s offspring: s s s w (generation 3) − He determined that smoothness dominated wrinkled 25% will not inherit the dominant trait Generation 3: Sw+ww offspring: Sw Sw ww ww & Sw + SS offspring: SS SS Sw Sw Mendel's Hypothesis: − Each parent contains both a dominant and recessive “particle” for the trait in question − They randomly pass on one or the other to each offspring − Each parent's contribution has a 50:50 chance which particle will be passed on, which means four possible combinations: Sw +Sw = SS or Sw or wS or ww Punnett Square: Today we refer to the “particles” for each trait as alleles. An allele is an alternate form of a specific gene. Homezygous dominant: Having two of the dominant form of an allele Heterozygous: Having one dominant and one recessive form Homozygous recessive: two of the recessive traits Monohybrid vs Dihybrid Crosses: Monohybrid: Crossing two plants that differ in only one characteristic Dihybrid: Crosses where the parent plants differed in two different characteristics Mendel's Principles: 1. The principle of segregation - offspring inherit one discrete unit for a trait from each parent - these units maintain their unique integrity from generation to generation 2. The principle of dominance and recessiveness - some expressions of a specific trait were dominant over others; at least one from dominant trait 3. The principle of independent assortment - Different traits were not inherited together as packages. They passed from generation to generation as independent units Problems: Mendel lucked out.. First of all, he happened to have selected traits that are influenced by single genes in the chromosomes of pea plants (monogenetic traits) Polygenic traits? Secondly: Some of Mendel's results were contrary to his principle of independent assortment Thirdly: Traits Mendel examined were types that are expressed as discrete categories, one thing or another – traits which are continuous in their potential forms Unit 3: Genetics: Cell Biology and Genetics Prokaryotic Cells – first appeared ~ 3.8 billion years ago Eukaryotic Cells ~ 1.5 billion years ago Basic Animal Cell Structure: Plasma membrane: sac that surrounds the cell; protects the cell; controls the movement of things in/out of the cell Cytoplasm: provides physical support organelles; source of nutrient materials Nucleus; Mitochondria: energy source; contain their own mitochondrial DNA Ribosomes: where protein synthesis takes place Endoplasmic Reticulum: More places for ribosomes to be; more
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