quantgeneticslecture1

quantgeneticslecture1 - Some ground rules Don't just sit...

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Some ground rules Don’t just sit there -- ask something! Interrupt me Read the book, but don’t panic if you are a little confused (however, it’s OK to panic if neither the lecture or the book make sense)
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Some concepts I will assume you understand Gene Dominant & recessive genes
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Quantitative Genetics The study of continuously varying traits
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Reading Assignment: Chapter 15 15.1Multifactorial traits . . . 15.2 Separating G and E 15.3 Managed evolution -- plant and animal breeding 15.4 Correlations among relatives 15.5 Pedigree studies and mapping QTL
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Causes of Continuous Variation Traits influenced by multiple genes Single-gene traits, but multiple alleles Traits also influenced by the environment
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Definitions of some closely related words Quantitative trait Continuous trait Multifactorial trait Polygenic trait
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Quantitative trait ! “continuous trait” A trait that varies over a continuous range Often used when little is known about the genetic control of a trait: – Phenotypes are obviously variable, – but not easily classified into discreet groups Term often used in plant and animal breeding We will talk later about QTLs Examples: Height, weight, crop yield
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Multifactorial trait A phenotypic character (trait) that appears to be controlled by multiple genes, but may also be controlled by environmental factors. Often used in the medical literature. Often associated term: “risk factors” Example: insulin-dependent diabetes, 12 known genes plus dietary habits.
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Polygenic trait A trait known to be controlled by multiple genes Strong genetic influence, but there can still be an environmental influence
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If a trait isn’t continuous -- what is it called? A Mendelian trait – Phenotypes easially classified into two or three groupes – Virtually no intermediate phenotypes – When crosses are made, the phenotypes occur in simple ratios (3:1, 1:2:1)
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Speaking of Mendel, why Speaking of Mendel, why did did he he get such clear-cut results? get such clear-cut results? ! He worked with commercial varieties of a self-pollinating species . (You would expect them to be almost completely homozygous at most loci.) Therefore, in any given cross there would be only two possible alleles . ! Working in a single uniform site , he minimized environmental variation. ! He purposely picked traits that were easy to score and that were relatively uninfluenced by the environment . ! The science of statistical analysis was a century off, so it was common practice to toss out data that “fit”
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Back to continuous traits: Back to continuous traits:
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Are continuous traits always controlled by multiple genes? controlled by multiple genes?
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This note was uploaded on 04/09/2008 for the course EFB 307 taught by Professor Powell during the Fall '07 term at Syracuse.

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quantgeneticslecture1 - Some ground rules Don't just sit...

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