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Unformatted text preview: IB35ac Class 8: Variation, Heritability Now that you've learned about how we evolved and how we got all around the world, now we'll start talking about how this has shaped the variation seen in our species. But what exactly is variation? How do you measure it? What causes it? How can we start to understand what variation is inherited and what's not? Darwin's theory relied on the observation that variation is inherited. This principle underlies heritability analyses, and we'll briefly discuss what this means (regression analyses and early estimates). IB35 Human Biological Variation Class #8 Typological Approach to Variation Plato Linnaeus Taxonomic nomenclature Naming a new species The type specimen (holotype) The paratypes Laid down foundations for binomial nomenclature Topics for today:
Variation, speciation, and heritability time is static... Single physical example of an organism known to have been used when the species was formally described Holotype Specimen # MVZ 43898 (skin & skull) Hall E. R. 1934. Univ. California Publ. Zool., 40(9):369 Canis latrans incolatus I Isaacs Lake, B iti h C l bi C L k British Columbia, Canada d Species Concepts Biological species concept = species are groups of interbreeding natural populations that are reproductively isolated from other such groups Evolutionary species concept = a lineage that maintains its integrity with respect to other lineages through both time and space Intro to Statistics mean = the average of all the items in a sample () variance = a measure of how spread out your data are (the mean of the squares of the differences between the respective samples and their mean) (2) = Standard deviation squared
Mean = 5'7.5" N=160 1 2 (x - ) =
N 2 2 X = one measurement (data point) = the mean = the sum of... N = the number of data points in your sample 2 2
->Variance increases, graph becomes stretched ->Variance decreases, graph becomes compressed Mean 2 (x - ) =
N 2 X = 2, 4, 3, 6, 2 = 3.4 = (2-3.4)2 + (4-3.4)2 + (3-3.4)2 + (6-3.4)2 + (2-3.4)2 Bimodal Distribution (-1.4)2 + (0.6)2 + (0.4)2 + (2.6)2 + (-1.4)2 1.96 + 0.36 + 0.16 + 6.76 + 1.96 11.2 N=5 2 = 11.2 / 5 = 2.24 Another Statistical Term
standard deviation = square root of the average squared deviation from the mean (square root of the variance) This is important because it tells you the dispersal around the mean in the units of your original data. 1 Standard Deviation includes 68% 2 Standard Deviations includes 95% 3 Standard Deviations includes 99.7% Although very small, this is never zero. *** This is a normal distribution. 2 Another Statistical Term
statistical significance = a measure of how much evidence we have against the null hypothesis Populational Approach to Variation No individual is the "ideal" You include time and geography Back to species concepts We need names so that we can talk about them, but you have to keep in mind that we are imposing nomenclature that organisms never asked for for. Looking at 2 populations Comparing means You have to consider the overlap... Length of tooth in cm 3 Some Old World Monkeys Largest and most diverse primate families today Macaques (genus Macaca) G l d baboons ( Gelada b b (genus Th Theropithecus) ith ) Baboons (genus Papio)
Macaques Geladas Baboons Histogram of Thero|Macaca|Phu
mean = 16.8mm; stdv = 1.08 Combined Histogram
Variables Thero Macaca Phu 16.0
mean = 15.8mm; stdv = 1.1 Cou unt 12.0 8.0 mean = 9.4mm; stdv = 1.8 4.0 0.0 5.0 6.9 8.8 10.6 12.5 14.4 16.3 18.1 20.0 Thero|Macaca|Phu Length of the third molar Tick Lion Baboon Chimp Human Species Concepts Biological Species Concept Defines species as a sexually interbreeding or potentially interbreeding group of individuals normally separated from other species by the absence of genetic exchange b f ti h Reproductive isolation a) Hybridization & therefore no speciation b) Isolation of gene pools Sympatric Speciation occurs between populations that occupy the same geographic range. a) Instantaneous Speciation b) Assortative mating of homozygotes Actual time Phylogeny Evolutionary Species Concept -Looks at morphology Allopatric Speciation is between populations that are geographically separated. What might make a population split? Types of Speciation Events Allopatric Sympatric F Four F Forces of Evolution f E l ti Drift Selection Mutation Migration/gene flow Population Level ->Only way to get genetic variation ->Individual level Genetic Drift - Change in the relative frequency with which an allele occurs in a population Selection - Basically natural selection: advantageous traits are selected for Gene Flow - Transfer of alleles of genes from one population to another 4 Species Concepts Biological Species Concept Monotypic Polytypic Holotype Specimen # MVZ 43898 (skin & skull) Hall E. R. 1934. Univ. California Publ. Zool., 40(9):369 Canis latrans incolatus I Isaacs Lake, B iti h C l bi C L k British Columbia, Canada d Taxon containing only one immediately subordinate taxon Taxon containing more than one sub-group at the next taxonomic level -Sub-species: Morphological differences but can still interbreed Papio hamadryas
P. h. anubis P. h. hamadryas Papio hamadryas cynocephalus Papio hamadryas ursinus mean = 15.33; stdv = 1.32; n = 63 mean = 16.79; stdv = 1.08; n = 130 Histogram of Phc|Phu
20.0 16.0 Variables Phc Phu P. h. cynocephalus Count P. h. P h papio 12.0 12 0 8.0 4.0 P. h. ursinus
0.0 10.0 11.3 12.5 13.8 15.0 16.3 17.5 18.8 20.0 Phc|Phu Anagenesis
(or, phyletic evolution)
Progress along a genetic evolution line thingy without branching off Evolution by Natural Selection in three parts:
1. The principle of variation 2. The principle of heredity 3. 3 The principle of differential fitness Evolution of species involving an entire population ->When enough mutations reach fixation ->Population significantly differentiates from an ancestral population ->New species name may be assigned ->Ancestral population can be considered extinct Millions of years ago a 5 Quantitative Genetics Decomposing the Total Variance
Continuously varying trait Heritability The proportion of the variance that can be attributed to genetic effects. Culture versus biology v TOTAL = v GENES + v ENVIRONMENT HOW TO CALCULATE HERITABILITY ->y-axis - offspring ->x-aix - parents ->scatterplot graph What does "heritability" mean?
2 2 p = g + e2
Number of individuals s 2 G h = 2 P 2
Heritability = the proportion of the total variance that is attributable to the effects of genes height Francis Galton Statistics Positive eugenics http://www.nature.com/scitable/topicpage/Estimating-Trait-Heritability-46889 6 ...
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This note was uploaded on 01/19/2011 for the course IB 35AC taught by Professor Hlusko during the Spring '08 term at University of California, Berkeley.
- Spring '08