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Adaptation Lecture 6: Adaptation and Evolution Pages 180-183 Pages 314-324 Evolution • _______ change in a population • Many different mechanisms of change • Ecology affects evolution and evolution affects ecology The phenotype is the expression of the genotype. • The phenotype is the outward expression of the genotype manifested in structure and function: – the genotype is a set of __________________ – the phenotype is the expression of the genotype as modified by environmental conditions affecting growth and development • An evolutionary solution and a genetically determined characteristic that improves an organism’s ability to survive in a particular environment. Genotype vs Phenotype • _________________ = genetic make-up of the individual being measured. • _________________ = visible manifestation of a character in an organism • Variation in plants and animals are a result of both genetics and environmental factors. Adaptation results from natural selection • Genotype is the unique genetic constitution of an individual. • Evolution is any change in the genetic makeup of a population. • _____________________________results in evolutionary change when genetic factors cause differences in fecundity and survival among individuals. • ________is the reproductive success of an individual. 1 Genetic Terms • Each chromosome carries units of heredity called_________________ • The position a gene occupies on a chromosome = locus • Genes occupying the same locus on a pair of chromosomes are called alleles Genes and alleles • Genes encode proteins: – used as part of an organism’s structure – may function as enzymes or hormones • Different forms of a particular gene are called _____________________: – alleles may cause perceptible and measurable differences in the phenotype (e.g., eye color) – defective alleles may cause genetic disorders: Allelic Diversity in Individuals • Each diploid individual has two copies of each allele: – a __________________ individual has two different alleles – a __________________ individual has identical alleles – alleles may be: • dominant (expressed in heterozygous individual) • recessive (masked by dominant allele) • codominant (result in intermediate phenotype in heterozygotes) – most deleterious alleles are recessive Gene pool • Basic evolutionary unit is the population • The total of all the genes in a population is the “__________________________” 2 The Hardy-Weinberg Law In 1908, Hardy and Weinberg independently described this fundamental law: the frequencies of both alleles and genotypes will remain constant from generation to generation in a population with: 1. 2. 3. 4. 5. a large number of individuals random mating no _______________ no ________________ no migration between populations Hardy-Weinberg equation A1 occurs with a frequency of 0.7 (70%) A2 occurs with a frequency of 0.3 (30%) • 0.7+ 0.3 = 1 • Therefore • A1 A1 : (0.72 = 0.49) • A2 A2 : (0.32 = 0.09) • A1 A2 : (2 x 0.7 x 0.3 = 0.42) • 0.49 + 0.09 + 0.42 = 1 Hardy-Weinberg equilibrium • Gene A has 2 alleles A1 (p) and A2 (q) • p + q =1 and (q=1-p) (p=1-q) Genotype A1 A1 A1 A2 A2 A2 Freqency p2 2pq q2 p2 + 2pq + q2 = 1 the proportions of all the genotypes in the population add up to 1 • Now, consider random mating in a population with … the allele frequencies (p (A) = 0.4 and q(a) = 0.6) • Then using simple binomial probabilities we get P2 + 2pq + q2 = 1.0 or in our case, 0.16 + 0.48 + 0.36 = 1.0 (AA) (Aa) (aa) Consequences of HardyWeinberg Law A population in HardyWeinberg equilibrium does not ____________ (no genetic change over time) if the random union of gametes continues Figure 16.4 • No evolutionary change occurs through the process of _____________ reproduction itself. • Changes in allele and genotype frequencies can result only from __________________ on the gene pool of a species. • Understanding the nature of these forces is one of the goals of evolutionary biology. 3 Conditions and violations of the HardyWeinberg Equation Condition for HardyWeinberg equilibrium Large population Corresponding Mechanism of Evolution if violated Genetic drift No net immigration or Gene flow emigration of alleles No differential mortality or Natural selection survival by genotype No new mutations Mutation pressure Gene flow • Emigration and immigration between populations can result in changes in allele frequencies or composition if the movement of alleles is ____________________________ Evolution by natural selection 1. Inherited variation exists for any character. – Phenotypic variation often reflects genotypic variation 2. Resources are limited → ________________ 3. Points 1 and 2 above results in individuals with a better genotype → more resources → more offspring than others in population Mechanisms of Evolution • ____________________ – stochastic (random) shifts in allele frequencies – typically occurs in small populations – chance events play a larger role in small populations but can occur in larger populations Natural selection • If allele frequencies remain in HardyWeinberg equilibrium THEN no differential mortality or reproduction associated with a given genotype • Differential representations of genotypes in future generations resulting from heritable differences due to survival or reproduction - ______________________________ Fitness • Fitness = relative genetic contribution of an individual’s descendants to future generations • __________________________ = expected number of offspring by a particular genotype • Relative fitness = relative representation of a genotype in the next generation 4 Sexual Selection Important properties of fitness 1. Fitness is a property of a____________, not of an individual or a population. 2. Fitness is specific to a particular _______________________. 3. Fitness is measured over one generation or more. • Some of an organism’s features are important in attracting ____________ • Sexual selection = selection by one sex for specific characteristics in individuals of the opposite sex, usually exercised through ______________________ behaviour….or • natural selection where fitness of one sex (often males) depends on their appeal to the other sex Kin Selection The peacock has an elaborate, brightly coloured tail • A form of genetic selection in which alleles differ in their rate of propagation because they influence the ___________________ of kin who carry the same alleles 3 components • Altruistic behaviour • __________________ fitness • Coefficient of relationship Inclusive fitness: Coefficient of relationship (the fraction of your genome shared with relatives from your common ancestors) Proportion shared Self full sibling half sibling father mother offspring grandparents niece/nephew uncle/aunt first cousin 100% 50% 25% 50% 50% 50% 25% 25% 25% 12.5% White fronted bee eaters in Kenya provide help at the nest. These birds are colonial nesters. Helpers tend to aid close relatives more frequently than distant relatives or unrelated birds. Breeders coeff. of relatedness father x mother 0.5 father x stepmother 0.25 mother x stepfather 0.25 son x nonrelative 0.25 uncle x nonrelative 0.125 grandmother x nonrelative 0.125 % cases 44.8 9.8 9.2 10.3 1.1 0.6 5 Evolution of interactions among species • __________________ = physical resemblance of 2 species resulting from advantages of similar appearance 2 parts: • Mimic = the imitative species • Model = the species the mimic resembles 3 fundamental types of mimicry 1. _____________mimicry: a benign species resembles a noxious or dangerous one. 2. Müllerian mimicry: several noxious species come to resemble each other • Bees, Wasps (and Ants) - The Order Hymenoptera venomous coral snake Sinaloan milk snake 3. ______________mimicry: a noxious or dangerous species comes to resemble a benign one. Zone-tailed hawk Turkey vulture Useful Conclusions from Population Genetics Studies • Every population harbors some genetic _______________ that influences fitness. • Changes in selective factors in the environment are usually met by evolutionary responses. • Rapid environmental changes caused by humans will often exceed the capacity of a population to _________________________ ; the consequence is extinction. 6