Modern Theory of Evolution

Hugo De Vries – botanist and geneticist Recognized that organisms of different species still share common phenotypes Concluded that there must be common genes in varied species. In the early 1900’s, through observations of new forms of flower species, he introduce the concept of mutations.

Modern Theory of Evolution Hugo De Vries – botanist and geneticist Mutation Theory stated that “mutations are the ultimate source of variation” It was later indicated that recombination during sexual reproduction and migration are also important factors.

Modern Theory of Evolution Individuals do not evolve but entire populations evolve if genetic make-up of the whole population is varied. The key to this is the importance of populations. A population is a group of organisms of the same species living together within a particular region.

A couple of Terms to sum it up. Allele Frequency – The number of particular alleles within a population. Gene Pool – The total of all the types of alleles in a population. Each allele occurs with a certain frequency. These frequencies may change as a result of natural selection. Therefore, evolution is a gradual change of allele frequencies in a population.

Hardy-Weinberg Law In 1908 Godfrey Harold Hardy and Wilhelm Weinberg showed that the segregation and recombination of genes in sexual reproduction could not by itself change the allele frequencies. The Law Ex. Allele p=90% - Ordinary random mating Allele q = 10% always produce the same frequencies.

Hardy-Weinberg Law For this constant allele frequency to occur, the following must be true: 1. The population must be large. 2. Individuals must not migrate into or out. 3. Mutations must not occur. 4. Reproduction must be random # 1 & 2 may exist # 3 & 4 almost never exist

Hardy-Weinberg Law So what is the big deal??? Enables us to demonstrate that evolution is occurring. The fact that populations change tells us that external factors cause the change. Failure of the law is considered evidence of Evolution.

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 p = frequency of one allele of a trait q = frequency of the other allele of the trait Frequency of homozygous dominant (TT) ---- p 2 Frequency of heterozygous dominant (Tt) pq Frequency of homozygous recessive (tt) ---- q 2

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 If the frequency of the widows peak allele is 70% and the non-widows peak allele is 30% (O.70) 2 + 2(0.70)(0.30) + (0.30) 2 = = 1 See, it works!! 1 = 1

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 This can be used to find the exact allele frequencies in the population. You need to know the percent of individuals with the recessive phenotype. If the allele frequencies are found to change over time (which does happen all the time), then this is seen as evidence of evolution.

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 Find the allele and genotype frequencies if the frequency of tongue rollers is 75% and non-tongue rollers is found to be 25%. q 2 = 0.25 p = 0.5 p 2 = pq = 0.5 tt = 25% tT = 50% TT = 25% q = 0.5 Because p + q = 1

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 Find the allele and genotype frequencies if the frequency of spotted frogs (S) is 64% and non-spotted frogs (s) is found to be 36%. q 2 = 0.36 p = 0.4 p 2 = pq = 0.48 tt = 36% tT = 48% TT = 16% q = 0.6 Because p + q = 1

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 Recall that if the allele frequencies are found to change over time, then this is seen as evidence of evolution. Suppose that in a population of salamanders, a dominant allele is for a horned snout and the recessive allele is for a blunt snout. If in 1985, 98% of the population had the horned snout and today, the horned snout population was found to be only 65%. Find the percent change in the allele frequencies and describe what could account for this change.

Hardy-Weinberg Principle p 2 + 2pq + q 2 = 1 Suppose that in a population of salamanders, a dominant allele is for a horned snout and the recessive allele is for a blunt snout. If in 1985, 98% of the population had the horned snout and 25 years later, the horned snout population was found to be only 65%. Find the percent change in the allele frequencies and describe what could account for this change q 2 = q 2 = 0.35 q = q = p = p = There has been a 45% change in the allele frequencies. The change in allele frequency is considered evidence of evolution. This could be due to a whole number of factors. A likely factor could be food availability and the blunt snout making it easier to eat a particular food.