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Lecture 5 - Lecture 5 Genetic Model Organisms/Pedigrees...

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Lecture 5: Genetic Model Organisms/Pedigrees Aneuploidy September 9, 2013 Extensions of Mendelian Genetics (Chapter 5) Continuous Characteristics Genetic model organisms – Why and how we use them – Examples • Pedigrees: Recognizing different patterns – Autosomal Recessive Traits – Autosomal Dominant Traits
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Lecture 5: Genetic Model Organisms/Pedigrees Aneuploidy September 9, 2013 • Pedigrees: Recognizing different patterns - X-Linked Recessive Traits – X-Linked Dominant Traits – Y-Linked Traits Aneuploidy (Chapter 9) Trisomy 21 (Down Syndrome) Chromosome morphology Karyotype
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Inheritance of Continuous Characteristics So far we have studied discontinuous characteristics: a few easily distinguished variations Continuous characteristics : a continuous distribution of phenotypes is observed examples: height, weight Also called quantitative characteristics .
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Inheritance of Continuous Characteristics When a single locus with two alleles encodes a characteristic, there are three genotypes possible: AA, Aa, and aa When there are two loci, each with two alleles, there are 3 2 = 9 genotypes The number of genotypes encoding a characteristic is 3 n n = number of loci with two alleles that influence the characteristic.
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Polygenic Traits So, if there are 8 loci, 3 8 = 6561 different genotypes. Many different phenotypes with only slight differences. Add in the environment, and there’s even more variation We’ll return to quantitative traits later (assuming we have time)
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Chapter 6: Genetic Model Organisms Genetic model organisms – Why and how we use them – Examples
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Genetic model organisms: why? The vast majority of organisms Use the same genetic material (DNA or RNA) Use the same genetic code Use many of the same genes to accomplish the same tasks. Indicates that all life on earth evolved from the same primordial ancestor (3.5-4 billion years ago) Thus, the study of other organisms can provide insight into human biology, and ultimately the treatment of disease.
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Genetic model organisms Organisms with characteristics that are particularly useful for genetic analysis: short generation time large number of progeny adaptable to lab environment housed and propagated relatively inexpensively genomes sequenced (recently)
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Genetic model organisms 7 major genetic model organisms Escherichia coli - a bacterium in the human gut Saccharomyces cerevisiae - baker’s/brewer’s yeast Caenorhabditis elegans - a microscopic nematode (round worm) Drosophila melanogaster - fruit fly Danio rerio - zebrafish (newbie - sequencing ongoing) Mus musculus - house mouse Arabidopsis thaliana - the thale cress plant Also Neurospora crassa - bread mold, and Zea mays - corn
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Example: Zebrafish and human skin color Zebrafish small vertebrates many progeny easy to raise in labs golden mutants were discovered in a pet store in Oregon in the 1970’s.
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