10.1.07 - Dr. Susan Foster BIOL 105 Evolution 10.1.07 I)...

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Dr. Susan Foster BIOL 105 – Evolution 10.1.07 I) Discrete (Qualitative) vs. Quantitative Traits 1) Qualitative (Discrete/Categorical) Traits a Can be categorized Red, blue, yellow, curly, straight b Are typically Mendelian (i) Influenced primarily by a single locus with few alleles (ii) Permits categorization c Are not absolutely uniform in phenotype within categories (i) Alleles show a dominant-recessive relationship Yielding two phenotypes Recessives can be either common or uncommon (ii) Alleles show an incomplete dominance relationship Phenotypes can show any pattern of relative abundance 2) Causes of Variation within Categories a Environmental variation (i) Variation in temperature, nutrients, predators etc. can influence phenotype b Loci of minor effect (i) Many loci can have minor effects on traits Think lateral plate expression 3) Quantitative Traits a Continuous traits (continuous variation) (i) Cannot be categorized Traits exhibit continuous variation in trait values that cannot be clearly divided into categories Ex. Japanese flounder (ii) Most of the trait variation you see E.g., height, length, hair color, leaf shape, egg size, seed size etc. b Character states usually exhibit a normal distribution (i) Normal distribution – balanced around the mean c Deviates from normal because: (i) Cannot measure infinitely finely Develop arbitrary categories Plot as a histogram
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(ii) Small sample size in empirical studies Sampling error will cause deviation from normal, even if it is a normal distribution Larger sample sizes will more closely approximate true distribution than will small The greater the standard deviation, the greater the spread will be around the mean d Quantitative Trait Loci Loci that influence quantitative traits Loci that have subtle effects 4) What can cause a continuous distribution of phenotypes (i) A mendelian trait with lots of alleles Multiple alleles at a single locus can produce continuous variation
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10.1.07 - Dr. Susan Foster BIOL 105 Evolution 10.1.07 I)...

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