Presentation on theme: "Genes and Evolution. What is a Population? Populations Evolve. Populations are groups of interbreeding individuals that live in the same place at the."— Presentation transcript:
What is a Population? Populations Evolve. Populations are groups of interbreeding individuals that live in the same place at the same time Individuals in a population compete for resources with each other.
Genes and Evolution Gene pool: the total collection of genes in a population at any one time Genetic variation: the differences genetically between individuals in a population Genotypic Frequencies: the frequency of genotypes (BB, Bb, bb) in the population which usually determines genetic variation Allelic Frequencies: the frequency of alleles (B or b) in the population which usually determines genetic variation
migration Introducing or removing genes from a population How do allelic frequencies change? mutation gene flow natural selection genetic drift non-random mating
Founder Effect When small populations move to new areas, the new populations will contain genes similar to the “founders”
differences in survival or reproduction leads to adaptation differences in“fitness” How does genetic structure change? mutation gene flow natural selection genetic drift non-random mating
How Does Natural Selection Work? Populations produce more offspring than the environment can support Some offspring have genetic qualities that makes survival easier. The unequal ability of individuals to survive and reproduce leads to the gradual change in a population over many generations
Survival of the Fittest Biological fitness is measured by the ability to reproduce –Cockroach (40 offspring/month) –Manatee (1 baby/ two years)
Types of Adaptations Protective Coloring –Camouflage –Mimicry –Aposematic Coloration Structural Adaptations –Structures that attract mates –Structures that help meet needs Behavioral Adaptations –Living in groups –Courtship Dance –Song Birds
Antibiotic Resistance: An Example of Natural selection Resistance to antibacterial soap Generation 1: 100% not resistant 0 resistant
Natural selection Generation 1: 100% not resistant 0% resistant Resistance to antibacterial soap
Natural selection Resistance to antibacterial soap mutation! Generation 1: 100% not resistant 0% resistant Generation 2: 96%not resistant 4% resistant This mutation is not a miracle gene. It codes for a protein that allows the bacteria to survive in the presence of the antibiotics.
Natural selection Resistance to antibacterial soap Generation 1: 100% not resistant 0% resistant Generation 2: 96% not resistant 4% resistant Generation 3: 76% not resistant 24% resistant
Natural selection Resistance to antibacterial soap Generation 1: 100% not resistant 0% resistant Generation 2: 96% not resistant 4% resistant Generation 3: 76% not resistant 24% resistant Generation 4: 12% not resistant 88% resistant
Selection on sickle-cell allele aa – abnormal ß hemoglobin sickle-cell anemia very low fitness intermed. fitness high fitness Selection favors heterozygotes (Aa). Both alleles maintained in population Aa – both ß hemoglobins resistant to malaria AA – normal ß hemoglobin vulnerable to malaria
genetic change by chance alone How does genetic structure change? mutation gene flow natural selection genetic drift non-random mating
Genetic drift 8 RR 8 rr Before: After: 2 RR 6 rr 50% R 50% r 25% R 75% r
The random population that survives a genetic drift event repopulates with a different frequency of genes.
mutation gene flow natural selection genetic drift non-random mating non-random allele combinations mating combines alleles into genotypes How does genetic structure change?
Non-Random Mating In nature, no species truly mates randomly. There is always a preference-usually with a mate that has similar genes. Selfish gene - a concept that individuals care more for others with similar genes. `
Artificial Selection Human-guided selection of traits –Dog Breeds –Crops Miniature horses were developed from multiple sources. Many different pony breeds were bred for small size, including the Shetland pony and the Dartmoor pony.
Co-Evolution Coevolution occurs when one species adapts to anothers adaptations Evolutionary Arms Race –Prey adapts to not be caught by predators –Predators adapt to catch prey
Darwin Awards In honor of Charles Darwin, the Darwin Awards commemorate those who improve our gene pool...by accidentally removing themselves from it. By necessity, the award is generally bestowed posthumously.
Darwin Award 2010 (1 January 2010, South Africa) Pop quiz, class. Do you or don't you go swimming in the crocodile-infested Limpopo? Do, or don't, leave your friends on the banks of the great grey-green Olifants River (main tributary of the Limpopo) and swim in its limpid waters not once, not twice, but three times the day you are finally devoured by that old crocodile? Let's just say it was a short New Year for Mariska B., 27, a waitress and former swimmer. According to a long-time resident of Phalaborwa, locals know, "You don't even put a toe in the river. It's teeming with crocodiles and hippos." This local, on her third refreshing dip of the day, didn't have time to scream or struggle. Friends saw just a ripple on the water where seconds before she had been swimming. Did I mention that swimming was strictly prohibited? Police searched for Mariska's body with long poles, and with the chemical detectors known as sniffer dogs, but found nothing. The cycle of life continues.
HARDY - WEINBERG If a population is evolving, the gene pool is changing. If a population that is not evolving, the gene pool is not changing and the population is said to be at Hardy–Weinberg equilibrium. The equilibrium is a reference point to determine how much a population is evolving. Biologists determine the rate of change by comparing the population’s genotype frequencies with Hardy–Weinberg equilibrium frequencies.
HARDY - WEINBERG To be at Hardy–Weinberg equilibrium the following must be true: –population is large –mating is random –no migration –mutation can be ignored –natural selection is not acting on the population.
HARDY – WEINBERG EQUATIONS Two Equations –Allelic Frequencies p + q = 1 »p is the frequency of one allele in decimal form (usually the dominant allele) »q is the frequency of the other allele (usually recessive) –Genotypic Frequencies p 2 + 2pq + q 2 = 1 »p 2 is the homozygous dominant frequency; it can be calculated at equilibrium using the allele frequency p »2pq is the heterozygous frequency »q 2 is the homozygous recessive frequency
HARDY-WEINBERG PROBLEM Given: In a population of 100 individuals (200 alleles), sixteen have attached earlobes (which are recessive). –Find the allele frequencies for A and a. –Find the genotypic frequencies of AA, Aa, and aa. Allele frequency –p + q = 1 or A + a = 1 –Homozygous Recessive (aa) = q 2 =.16 q =.4 or 40% –p + q = 1 or 100% –p +.4 = 1 –p =.6 or 60% –or A =.6 and a =.4
HARDY - WEINBERG PROBLEM Genotypic frequencies –If: p =.6 and q =.4, then p 2 = (.6)(.6) =.36 q 2 = (.4)(.4) =.16 2pq = 2(.6)(.4) =.48 Therefore, in the population: –Homozygous dominant = 36/100 or 36% –Heterozygous dominant = 48/100 or 48% –Recessive = 16/100 or 16%
ANOTHER PROBLEM Fraggles are mythical, mouselike creatures that live beneath flower gardens. Of the 100 fraggles in a population, 91 have green hair(F) and 9 have grey hair(f). Assuming genetic equilibrium: –What are the allelic frequencies of F and f? –What are the genotypic frequencies?
ANSWERS TO PROBLEM Gene frequencies: –F = 0.7 and f = 0.3 Genotypic frequencies –FF = 49% or 0.49 –Ff = 42% or 0.42 –f f = 9% or.09
HARDY-WEINBERG & EVOLUTION If a populations actual frequencies match the HW frequencies, then the population is not changing— not evolving. Conversely, if the actual frequencies do not match the HW frequencies, then the frequencies have been changed—evolution has occurred. Causes of allele frequency variations –Mutation –Gene Flow –Natural selection –Genetic drift –Non-random mating How often in nature do NONE of these occur? –Rarely, if ever.