* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download reproductively separated
Survey
Document related concepts
Gene expression programming wikipedia , lookup
Genetic engineering wikipedia , lookup
Genome (book) wikipedia , lookup
Genetics and archaeogenetics of South Asia wikipedia , lookup
Hybrid (biology) wikipedia , lookup
Hardy–Weinberg principle wikipedia , lookup
Group selection wikipedia , lookup
Designer baby wikipedia , lookup
Human genetic variation wikipedia , lookup
Dominance (genetics) wikipedia , lookup
Polymorphism (biology) wikipedia , lookup
Genetic drift wikipedia , lookup
Population genetics wikipedia , lookup
Transcript
Isolation and speciation Key words: Natural selection and evolution Gene pool Explain how natural selection can lead to a change in allele frequencies (evolution) within a gene pool. Allelic frequency • Variation (due to mutation, meiosis + random fertilisation of gametes) • Advantageous allele • Individuals survive and reproduce • Advantageous allele passed on • Repeats over generations • Allele becomes more common in the gene pool= change in allele frequency Types of selection and conditions they occur? • Stabilising- eliminates extremes of the phenotype range; constant environmental conditions • Directional- favours one extreme of the phenotype; environmental change • Disruptive- favours both extremes of the phenotype; an environmental factor takes 2 or more distinct forms (e.g. temperature)- most important in bringing about evolutionary change. Environmental factors affect the probability of a gene being passed on and its frequency within the gene pool Speciation The evolution of a new species from existing ones. Definition of species? • similar characteristics • breed • fertile offspring Members of a species are reproductively separated from other species. How new species are formed: Bullet point: • Within a species are a number of populations • A population becomes separated from the others • Undergoes different mutations • Different environments • Different selection pressures • Change in allele frequency • Populations unable to interbreed Diagram: 2 forms of speciation Allopatric 2 populations geographically separated Physical barrier- ocean, river, mountain range, desert If environmental conditions vary Different selection pressures Change in allele frequencies New species formed Rich questions: - Explain what happens to cause speciation. - How do the mechanisms of reproductive isolation differ in allopatric and sympatric speciation? Sympatric A population in the same area becomes reproductively separated. e.g. apple maggot fly http://media.hhmi.org/biointeractive/fil ms/OriginSpecies-Lizards.html Genetic drift • Small populations • Few alleles • Those passed on increase in frequency in gene pool • Population changes rapidly • Genetic drift greater • More likely that speciation will occur http://nortonbooks.com/college/biology/ani mations/ch16a01.htm • Large populations - How is genetic drift fundamentally different to natural selection? - Why does genetic drift only have noticeable effects in small populations?