Evolutionary Change Without Selection Section 8.1

Evolutionary Change without Selection Learning Goal: To explore causes of evolutionary change that are not influenced by the traits of individuals. Success Criteria: I know I am succeeding when I can… discuss genetic drift, and the consequences of the founder effect and bottlenecks describe the Hardy-Weinberg principle explain how human activities affect the evolution of other species Not all evolutionary changes are result of NS Sometimes changes in genetic makeup of pop. not influenced by traits of individuals These changes tend to reduce genetic diversity within pop

Genetic Drift Genetic Drift: changes to allele frequency as a result of chance more pronounced in small populations can result in a particular allele becoming either very common or disappearing entirely over a number of generations lost alleles reduce genetic diversity of the population

Bottlenecks and the Founder Effect Bottleneck Effect: a dramatic, often temporary, reduction in population size, usually resulting in significant genetic drift Pop of 10000 reduced to 50, unlikely to contain all alleles found in larger pop Many alleles, particularly rare alleles likely to be eliminated If pop recovers, genetic makeup limited to alleles carried by 50 indiv and any new mutations

Bottlenecks and the Founder Effect Cont’d… adverse consequences for populations ex. cheetahs cheetahs are descendants of a population that experienced a severe bottleneck event 10, 000 years ago which left only 7 cheetahs reduced genetic variability in the population as a result cheetahs are vulnerable to disease, have low reproductive success and high juvenile mortality rates Similarly, the northern elephant seal population was reduced by overhunting to 20 individuals in the 1890s. Although the population has rebounded to over 127 000 individuals, they are genetically very similar.

Bottlenecks and the Founder Effect Cont’d… Founder Effect: genetic drift that results when a small number of individuals separate from their original population and establish a new population new population may begin with a different frequency of alleles Original pop has allele in 1 of 1000 finches (0.1%) Suppose by chance, 1 of only 20 finches on new island carry allele That’s 5%, an increase of 50 times Doesn’t increase diversity, but new pop begins with different gene pool

Hardy–Weinberg principle Hardy–Weinberg principle Hardy–Weinberg principle: in a stable and non-evolving population, gene frequencies remain the same unless acted upon by evolutionary forces - mathematically, a gene pool can be described by the frequency of each of the alleles within a pop

Hardy–Weinberg principle Hardy–Weinberg principle… serves as a control in population studies tells us what to expect if a population is not evolving If results suggests otherwise, then the population must be evolving, and we can then study the causes such as…. natural selection: favours the passing on of some alleles over others small population size: increases the likelihood of genetic drift mutation: introduces new alleles to a population immigration or emigration: introduces or removes alleles in a population horizontal gene transfer: the gaining of new alleles from a different species - Any factor that causes allele frequency to change leads to evolutionary change

Consequences of Human Influence human activities (such as harvesting species, altering habitats and polluting the environment) have a very strong selective influence on many species and therefore influence their evolution ex. climate change in some cases is happening to rapidly for species to adapt such as with caribou that live in the Artic *Refer to table on page 334*

Evolutionary Change without Selection Learning Goal: To explore causes of evolutionary change that are not influenced by the traits of individuals. Success Criteria: I know I am succeeding when I can… discuss genetic drift, and the consequences of the founder effect and bottlenecks describe the Hardy-Weinberg principle explain how human activities affect the evolution of other species This lesson will present the many forms of evidence that convinced Darwin that species had changed over time and that species appeared to share a common ancestry. The basis of his theory on the evolution of species.

Homework 8.1 questions #9-11, 13 &14