UCSB EEMB 2 - Lec #11 EEMB 2 SM17 1S (Adaptation-Variation) (1) (15 pages)

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Lec #11 EEMB 2 SM17 1S (Adaptation-Variation) (1)



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Lec #11 EEMB 2 SM17 1S (Adaptation-Variation) (1)

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Pages:
15
School:
University of California, Santa Barbara
Course:
Eemb 2 - Introductory Biology III
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Adaptation and Variation The Evolutionary process 1 Variation 2 Natural Selection 3 Genetic Divergence 4 Reproductive Isolation 5 Speciation Variation Natural Selection Genetic Divergence Reproductive isolation Speciation Populations evolve not individuals Populations have variation in traits among individuals Microevolution The change in allele frequencies in a population over generations Adaptation and Variation Features that characterize a population 1 Morphological traits Form 2 Physiological traits Function 3 Ethological traits Behavior In reproducing species there is variation in most traits in individuals Individuals of a population vary in their traits Discrete characters either or basis 2 or more distinct forms Quantitative characters vary along a continuum Adaptation and Variation Variation Traits may be positive negative or neutral to individuals in a population survival and reproduction Adaptation Adjustment or change to meet environmental conditions 1 Adaptive Traits form of trait that is an advantage in terms of survival reproduction 2 Maladaptive Traits form of trait that is a disadvantage in terms of survival reproduction 3 Neutral Traits 0 form of trait that is neither a disadvantage or advantage in terms of survival and reproduction Almost every trait or every species is variable Adaptation and Variation Variation Where does variation come from Information about heritable traits occurs in genes Gene Hereditary unit of DNA that codes for specific traits Alleles 2 or more different molecular forms of a gene alternate form of a gene dominant recessive incomplete dominance Gene Pool All the genes in a population pool of genetic resources Genome All the genes in a species Genotype Individuals inherit different combinations of alleles genetic expression Phenotype Individuals express different details of traits physical expression Adaptation and Variation Variation Individuals inherit different combinations of alleles which leads to variation in phenotype Which alleles end up in a given gamete and individual 5 events 1 Gene mutation produces new alleles 2 Crossing over at meiosis I puts novel combinations of alleles in chromosomes 3 Independent assortment at meiosis I puts mixes of maternal and paternal chromosomes into gametes 4 Fertilization combines alleles from two parents 5 Change in chromosome number or structure the loss duplication or repositioning of genes Ex Each human gamete 10600 possible allelic combinations Adaptation and Variation Phenotypic Frequencies The abundance of phenotype in a population Ex Eye color gross simplification Brown 25 BB Brown 25 50 X 100 50 Blue 40 20 50 X 100 Green 3 50 X 100 6 Hazel 2 50 X 100 4 100 Blue 20 bb Green 3 Hazel 2 Phenotype Frequency Each genotype has a distinct phenotype Adaptation and Variation Allele Frequencies The abundance of each kind of allele in a population Ex Wildflowers Flower color incomplete dominance 2 alleles A a Red White Pink Pop Size 320 AA AA Aa aa Aa 20 aa 320 X 2 640 160 X 1 160 800 A alleles 20 X 2 40 160 X 1 160 200 a alleles 160 Aa 500 Diploid 1000 copies of genes 800 1000 0 8 80 A allele 200 1000 0 2 20 a allele 100 A a Alleles With this information can track the rate of genetic change over multiple generations Adaptation and Variation Allele Frequencies Is there genetic change over generations Genetic equilibrium The frequencies of alleles at a given gene locus stable for multiple generations remain Question 1 How do we know whether or not a population is evolving with respect to any trait Answer Hardy Weinberg Principle 1908 Mathematical formulation to describe how to maintain the frequencies of alleles of a population over time Adaptation and Variation Hardy Weinberg Principle 1908 In a population in genetic equilibrium 1 The proportion of genotypes at one gene locus with two kinds of alleles Binomial Expansion p2 AA 2pq Aa q2 aa 1 p the frequency of allele A q the frequency of allele a The rule is allele frequencies will be stable through successive generations if 1 there has been no gene mutations 2 the population is very large 3 the population is isolated 4 the gene has no effect on survival and reproduction 5 mating is random Adaptation and Variation Hardy Weinberg Equilibrium Example Butterfly wing color pairs of genes on pairs of homologous chromosomes 1 Assume the population is at equilibrium 2 Pair of alleles is for wing color allele A dark blue wings allele a white wings Heterozygote Aa light blue wings incomplete dominance 3 The frequencies of A and a must add up to 1 in the population p q 1 AA Aa aa Adaptation and Variation Hardy Weinberg Equilibrium 4 During meiosis each allele segregates from its partner and ends up in separate gametes p the proportion of gametes carrying the A allele q the proportion of gametes carrying the a allele Expected frequencies of the 3 genotypes AA aa Aa in the next generation p A q a p A AA p2 Aa pq q a Aa pq aa q2 The frequencies of the genotypes add up to 1 p2 AA 2pq Aa q2 aa 1 Adaptation and Variation Hardy Weinberg Equilibrium Example 1000 butterflies each produces 2 gametes 490 420 90 AA individuals produce 980 A gametes Aa individuals produce 420 A and 420 a gametes aa individuals produce 180 a gametes 2000 gametes The frequency of A and a alleles among the 2000 gametes p 980 420 2000 0 7 70 A q 420 180 2000 0 3 30 a Adaptation and Variation Hardy Weinberg Equilibrium At fertilization 1 Gametes combine at random give rise to the next generation 2 Assume population remains constant at 1000 individuals p2 AA 0 7 X 0 7 0 49 X 1000 2pq Aa 2 X 0 7 X 0 3 0 42 X 1000 490 AA individuals 420 Aa individuals q2 aa 0 3 X 0 3 0 09 X 1000 90 aa individuals p2 AA 2pq Aa q2 aa 0 49 0 42 0 09 1 Allele frequencies have not changed A 2 X 490 420 2000 1400 2000 0 7 p a 2 X 90 420 2000 600 2000 0 3 q Genotype frequencies have not changed 49 42 09 Adaptation and Variation Hardy Weinberg Equilibrium As long as the 5 basic assumptions are met The frequencies stay the same through successive generations Test by calculating frequencies in the gametes of the next generation F1 genotypes 0 49 AA 0 42 Aa 0 09 aa A Gametes A A a a 0 49 0 21 0 21 0 09 0 7 A 0 3 a a This is the exact starting point values same as original gametes Allele frequencies and the range of values for wing color will not change Adaptation and Variation Hardy Weinberg Equilibrium When genotypes and phenotypes do not match the predicted proportions 1 Indicates that 1 or more conditions assumptions of


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