I Evolution a change in allele or genotype frequency in a population over time A How genotypes and phenotypes change over time B More basically it is a change in the genetic makeup of a population over time C Based mainly on genes D Genetic Variation 1 Penguins have more genetic variation than humans because they have evolved longer 2 However their physical differences may seem slim as opposed to humans E POPULATIONS EVOLVE NOT INDIVIDUALS II Population Genetics A The study of patterns of genetic variation 1 Species group of organisms capable of interbreeding a Natural selection does not change genes it just selects them 2 Gene Pool collection of all alleles present in the individuals of a species 3 Populations interbreeding groups of organisms of the same species living in the same geographical area III What can cause genetic variation A Mutation gradual change in genetic code 1 Somatic any cells that don t give rise to gametes skin 2 Germ Line can be passed on 3 Mutations can be a Deleterious b Neutral i Random changes to the working parts of complex organized systems are almost always deleterious harmful i Many mutations however have little or no effect on the organism ii These mutations are neither deleterious nor advantageous because they occur in regions of the genome that are not functionally important iii Such mutations are termed neutral c Advantageous i Occasionally a mutation occurs that is actually beneficial in terms of survival or reproduction ii Mutations like these are considered advantageous if they improve their carriers chances of survival or reproduction iii Advantageous mutations as we will see can increase in frequency in a population until eventually they are carried by every member of a species iv These mutations are the ones that result in a species that is adapted to its environment better able to survive and reproduce in that environment B Recombination to shuffle portions of a gene or combine with another one IV Allele Frequencies A B Example 1 The genotypes for pea color in Mendel s pea plants a What are the frequencies of the a and A alleles if every plant is green C Example 2 A population of 100 pea plants has the following genotype frequencies 1 AA yellow pea plant 2 Aa yellow pea plant 3 aa green pea plant 1 50 aa 2 25 Aa 3 25 AA V Measuring Genetic Variation a What is the frequency of a A Alleles are different forms of a gene B Allele frequencies the rate of occurrence of different alleles in the population C The allele frequency in population provides a measure of genetic variation for one gene in a given population VI Measuring Genotype Allele Frequencies A Observable Traits phenotype 1 Example ladybug a Is it black with red spots b Or red with black spots B Gel Electrophoresis genotype 1 Gel electrophoresis separates segments of DNA according to their size 2 In gel electrophoresis the proteins being studied migrate through a gel when an electrical charge is applied creating an electrical field 3 The rate at which the proteins move from one end of the gel to the other is determined by their charge and their size 4 Proteins with more negatively charged amino acids migrate more rapidly toward the positively charged end and vice versa 5 Only shows alleles C DNA sequencing 1 Uses gel electrophoresis to determine the exact sequence of the gene 2 DNA Molecule nucleotides a A G C T b Example segment of a gene AGTTAGCTA D Example observe differences in the alcohol dehydrogenase ADH gene in 50 fruit flies 1 In sequencing the gene we find 70 that have an A and 30 that have a G at a given position in the gene a Allele frequency for A 70 100 or 70 b Allele frequency for G 30 100 or 30 VII Evolution A Example VIII Hardy Weinberg Conditions 1 Generation 1 of a population has 200 copies of the blue eye allele 2 Generation 2 of the population of the same size has 300 copies of the same allele A A set of calculations standards to create a criteria list for a non evolving population starting point 1 There can be no differences in the survival and reproductive success of individuals 2 Populations must not be added to or subtracted from by migration 3 There can be no mutation 4 The population must be sufficiently large to prevent sampling errors 5 Individuals must mate at random B Criteria for equilibrium 1 Two 2 alleles from each population when added must equal 1 2 Proving there is no evolution IX Hardy Weinberg Relation A X Natural Selection A Charles Darwin father of evolution 1 Was studying to become a priest theologist 2 Most interested in birds 3 What he found a Published in 1859 in On the Origin of Species b Species are not unchanging they have evolved over time c Suggested natural selection brings about adaptation d Organisms adapt to their environment adaptation B Thomas Malthus 1 Essay on the Principle of Population a Populations have potential to increase exponentially but this does not occur b Limited resources 2 Which individuals will win the competition XI Types of Selection A Positive B Negative C Balancing 1 Natural selection that increases the frequency of a favorable allele 1 Natural selection that decreases the frequency of a harmful allele 1 Acts to maintain 2 or more alleles in a population a Natural selection that maintains an allele at some intermediate frequency between 0 and 100 b Heterozygote Advantage i Another example of balancing selection occurs when the heterozygote s fitness is higher than that of either of the homozygotes resulting in selection that ensures that both alleles remain in the population at intermediate frequencies ii This form of balancing selection is called heterozygote advantage and it is exemplified by human populations in Africa where malaria has been a long standing threat iii Because the malaria parasite spends part of its life cycle in human red blood cells mutations in the hemoglobin molecule that affect the structure of the red blood cells have a negative impact on the parasite and can reduce the severity of malarial attacks XII Patterns of Natural Selection A XIII Stabilizing Selection A Stabilizing selection maintains the status quo and acts against extremes 1 A good example is provided by human birth weight a trait affected by many factors including many fetal genes Fig 21 10 2 If a baby is too small then its chances of survival after birth are low 3 However if it is too big there may be complications that endanger both mother and baby during delivery 4 Thus the optimum birth weight is between these two
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