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Set 1 Mandelian Genetics Notes.docx

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BIOL 239
Christine Dupont

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Set 1 Mandelian Genetics 2/19/2013 10:30:00 PM Genetic traits are passed on from one generation to the next  Artificial selection-purposeful matings o Domesticated plants and animals  Dogs-domesticated wolves. Most compatible wolves were bred o The version of the gene in dogs and wolves are different but they have the exact same genes  1950s Belyaev-Scientific American o A forgotten Russian experiment in fox domestication  Gregor Mendel (1822-1884) o Augustinian monk and expert plant breeder (Austria 1800s) o Experiments with garden peas Advantages to Mendel’s approach  Garden peas: easy to cross-fertilize, large numbers of offspring, short growing season  Clear-cut alternative forms of particular traits: purple vs. white flowers, yellow vs. green peas, round vs. wrinkled peas =phenotype  Establishment of pure-breeding lines: offspring carry parental traits that remain constant from generation to generation  Carefully controlled breeding: Use of reciprocal crosses and self- feritilization Phentotype= observable characteristic (largely determined by genotype)  -commonly referred to as a trait Genotype= genetic make-up; description of genetic information carried by an individual Mendel’s experiments with garden peas Cross-fertilization  Mendel used selective breeding to produce true-breeding lines of peas o Offspring always showed same phenotype as the parent plants  Mating of parents with antagonistic traits produced hybrids o Green x yellow-> yellow o Round x wrinkled -> round o Purple x white -> purple o Long x short -> long  Found a consistent pattern of inheritance, from which he based his theories Prior to Mandel  Theories that one parent contributes most to an offspring’s inherited features (disproved through reciprocal crosses)  Parental traits become mixed and forever changed in the offspring (disproved through reappearance of recessive traits) Monohybrid crosses  Mating between individuals that differ in only one traits o Dwarf x tall -> tall (monohybrid) –All F1 progeny resembled one of the parental strains  Tall x tall -> 787 tall and 277 dwarf –In F2 progeny, lost trait reappeared Discrete units of inheritance are alleles of genes. Alleles are alternative forms of a single gene.  Hypothetical example o Lets say each of the following features is determined by a single gene  Gene Alleles  Trait:  Eye pigment brown or blue  Skin pigment albino or pigmented  Height tall or short  Hair texture curly or straight  Seed texture(peas) smooth or wrinkled o Most human traits (including the above) are determined by multiple genes with multiple alleles.  A gene may have several alleles that normally occur in a population o =polymorphic  but a maximum of two for one gene can exist in a diploid individual e.g, humans  Some genes have only one allele that is normally present in a population o =monomorphic Mendel’s Law of Segregation  The two alleles for each trait separate (segregate) during gamete formation, then unite at random, one from each parent, at fertilization. o Describes how alleles of 1 gene behave  Each parent carries 2 copies of each gene o Specific allele exists for each gene o Each individual receives 1 from each parent  The punnett square o Monohybrids- Two different alleles for a single gene that determines a single feature  Genotype vs. Phenotype o Homozygous dominant- GG -> yellow o Heterozygous (dominant and recessive allele)- Gg -> yellow o Homozygous recessive- gg -> green o Dominant and recessive are terms used to describe the phenotypic effect of different alleles At the DNA level, different alleles differ in nucleotide sequence. This results in changes in the amino acid sequence or the amount of protein.  E.g trait: texture: round(smooth) or wrinkled, alleles: round(W) or wrinkled (w), gene: codes for the enzyme starch-brinching enzyme 1 (SBE1)  Mutation causes amino acid change resulting in inactive SBE1 o Which also results in a change in phenotype  WW large amounts of branched insoluble starch  ww no branched starch o In ww, soluble starch builds
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