BIO370lec5 - Lecture 5 Populations I Genotypes vs....

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Unformatted text preview: Lecture 5 Populations I Genotypes vs. Phenotypes A phenotype is the external characteristics of an individual this is what selection can act on (genotype + environment) A genotype is the set of genes carried by an individual Biological evolution is an inherited change in a group of organisms through time Inherited changes can be manifested as changes in phenotype Inheritance in Populations Populations : a group of interbreeding individuals and their offspring Populations EVOLVE! How do we describe phenotypic variation in populations? Variation in some traits is discrete Variation in other traits is continuous What is a distribution? A distribution tells us how frequent different things are A discrete distribution A continuous distribution Wrinkled Smooth Height Frequency What is a variance? A specific measure of variability The average distance from the mean 2 = the average of (X-X) 2 Ranges from zero to infinity (can never be negative) NO VARIANCE = NO EVOLUTION ! Example: Half the bulls in a longhorn herd have horns 3 wide, half have horns 5 wide Mean: x = 4 Variance: 2 = (1/2)(3 - 4) 2 + (1/2)(5 - 4) 2 = 1 ft 2 What is a correlation? A measure of association between two variables Ranges from -1 to +1 Weight Height Negative correlation r = 0.7 Length of my lecture Amount you remember No correlation r = Positive correlation r = 0.7 Color/Length correlation 25.00 27.00 29.00 31.00 33.00 35.00 37.00 39.00 0.00 10.00 20.00 30.00 40.00 50.00 60.00 Corolla Tube Length Pigment concentration Monogenic traits = discrete phenotypes 4 6 8 10 12 14 16 PL 50 100 150 200 C o u n t 0.0 0.02 0.04 0.06 0.08 0.10 0.12 0.14 0.16 0.18 P r o p o r t i o n p e r B a r Most traits are continuously distributed differ in degree rather than kind It is relatively hard to find traits like Mendel studied! Francis Galton Karl Pearson ~1900 Discrete traits eye color color vision sickle-cell anemia Tay-Sachs Syndrome thalassemia hemophilia tongue curling attached earlobes hitchhiker thumb Continuous traits heart disease obesity cancer susceptibility diabetes vision almost anything & everything in plants Continuous traits generally do not show segregation of particular phenotypes!...
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BIO370lec5 - Lecture 5 Populations I Genotypes vs....

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