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MECHANISMS OF EVOLUTION: GENETIC VARIATION

MECHANISMS OF EVOLUTION: GENETIC VARIATION. Quantity of DNA and the number of genes are highly variable among species Variation within a species is the result of the variety & random recombination of alleles possessed by individuals

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MECHANISMS OF EVOLUTION: GENETIC VARIATION

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  1. MECHANISMS OF EVOLUTION:GENETIC VARIATION Quantity of DNA and the number of genes are highly variable among species Variation within a species is the result of the variety & random recombination of alleles possessed by individuals Results in a high degree of genetic diversity within most populations

  2. MECHANISMS OF EVOLUTION:GENETIC VARIATION • Recall the following terms: • Genes • Alleles • Homozygous • Heterozygous • Genome • Genotype • Phenotype • Population

  3. GODFREY HAROLD HARDY Wilhelm Weinberg

  4. MECHANISMS OF EVOLUTION:Hardy-Weinburg Principle Allele frequencies will not change from generation to generation as long as the following conditions are met: Large population

  5. 2) Mating opportunities are equal

  6. 3) No mutations occur

  7. 4) No migration occurs

  8. 5) No natural selection occurs – all individuals have an equal chance of reproduction

  9. Hardy-Weinburg Principle • For a gene with two alleles (A and a), the Hardy-Weinburg Principle can be expressed using the equations below: If p = frequency for allele A and q = frequency of allele a Then…. p + q = 1 (p + q)2 = 12 p2 + 2pq + q2 = 1

  10. MECHANISMS OF EVOLUTION:HARDY-WEINBURG PRINCIPLE p2 = frequency of AA genotype 2pq = frequency of Aa genotype q2 = frequency of aa genotype

  11. MECHANISMS OF EVOLUTION:HARDY-WEINBURG SQUARE

  12. PROBLEM #1 A population has only two alleles, R and r for a particular gene. The allele frequency of R is 20 % a) What are the frequencies for RR ? b) What are the frequencies for Rr ? c) What are the frequencies for rr ?

  13. PROBLEM #1 No problem… Step 1….. Write down all givens Got a problem ?

  14. Step #3 How is what you are being asked, related to what you know ? Then solve ! Step #2 What are you being asked ?

  15. SOLUTION GIVENS: p = 0.20 I KNOW THAT :p2 + 2pq + q2 = 1 q = 0.80 Substitute values for p and q (.20)2 + 2(.20)(.80) + (.80)2 = 1 0.40 + 0.32 + 0.64 = 1 Congratulations ! You did it Frequency of RR genotype = 0.04 or 4 % Frequency of Rr genotype = 0.32 or 32 % Frequency of rr genotype = 0.64 0r 64 %

  16. PROBLEM # 2 In a moth population of 100 individuals there are 5 individuals who are recessive (light grey ww) for wing color: a) How many are homozygous (WW) dominant ? b) How many are heterozygous (Ww) dominant ? Write out your givens !

  17. SOLUTION Given: q2 = 5_ 100 p + q = 1 p= 1 - q q2 = 0.05 p = 1 – 0.2236 q = 0.2236 p = 0.7764 FIND 2pq FIND p2 b) 2pq = 2(0.7764) (0.2236) a) p2 = (0.7764)2 2pq = 0.3472 p2 = 0.6028 Therefore there are 35 individuals who are heterozygous Therefore 60 individuals are homozygous dominant Grade 12 Biology Rocks

  18. MECHANISMS OF EVOLUTION:RANDOM CHANGE • Genetic Drift = changes to allele frequency as a result of chance: such changes are much more pronounced in small populations • Evolution = defined in genetic terms as any change in gene (and allele) frequencies within a population

  19. Genetic Drift • In small populations, chance can play a huge role in altering allele frequencies • When a severe event results in a drastic reduction in numbers, a population may experience a bottle-neck effect • In this form of genetic drift occurs, a very small number of sample alleles survives to establish a new population • Their relative frequency may differ those in the original population & additional genetic drift may result in further changes in the gene pool

  20. MECHANISMS OF EVOLUTION:Genetic Drift

  21. BOTTLENECK EFFECT Occurred in the northern elephant seal population Population was reduced to 20 individuals in 1890’s and has rebounded to over 20 000 by 1974 Genetic tests show 24 loci tests showed total homozygosity Northern Elephant Seal Distribution

  22. FOUNDER EFFECT • Founder effect = genetic drift that results when a small number of individuals separate from their original population and find a new population

  23. PATTERNS OF SELECTION • 3 types of selection pressures • Stabilizing Selection= selection against individuals exhibiting variations in a trait deviate from the current average

  24. PATTERNS OF SELECTION 2. Directional Selection Pressure= Selection that favours an increase or decrease in the value of a trait from the current population average

  25. PATTERNS OF SELECTION 3. Disruptive Selection Pressure= Selection pressure that favours two or more variations or traits that differ from the current average

  26. PATTERNS OF SELECTION 4. Sexual Selection Pressure: Different reproductive success that results from variation in the ability to obtain mates: results in sexual dimorphism and mating courtship behaviours

  27. PATTERNS OF SELECTION • Not all species show obvious sexual dimorphism • In some species of penguin, males & females look the same and they have a hard time telling each other apart • A male picks up a stone & drops it at the feet of a would-be-mate. If the other penguin is a male, the offering is rejected

  28. ALTRUISM Altruism = behaviour that decreases the fitness of an individual that is assisting or cooperating with a recipient whose individual fitness is increased

  29. SPECIATION: The formation of a new species • Species = members or breeding groups or populations that are reproductively isolated from other groups and evolve independently • Speciation evolutionary formation of a new species • Reproductive Isolating Mechanisms are any behavioral, structural or biochemical traits that prevent individuals from different species from reproducing together

  30. REPRODUCTIVE ISOLATING MECHAMISMS: Prezygotic Isolating Mechanisms Lion • Pre-zygotic mechanisms include: • Ecological isolation: species occupy different habitats or separate niches Ex) lions = savannah animals tigers = forest animals Could mate and hybridize if found together and produce ligars Tiger Liger

  31. REPRODUCTIVE ISOLATING MECHAMISMS:Prezygotic Isolating Mechanisms 2. Temporal Isolation = similar plants bloom at different times of the day, night, month/seasons. This leaves no change of hybridization since reproductive cycles or mating occurs at different times Spring Iris Summer Iris

  32. REPRODUCTIVE ISOLATING MECHAMISMS: Prezygotic Isolating Mechanisms 3. Behavioural Isolation = Each species may use different signals for attracting a mate. Use the wrong dance, misinterpret the dance, and you are breakfast, lunch, or dinner

  33. REPRODUCTIVE ISOLATING MECHAMISMS • Ecological isolation, temporal isolation & behavioural isolation are all pre- zygotic isolating mechanisms • These mechanisms prevent interspecies mating • Another prezygotic isolating mechanism is the prevention of fertilization. There are two mechanisms that prevent fertilization:

  34. REPRODUCTIVE ISOLATING MECHAMISMS:Prevention of Fertilization Who Is He Kidding ? • Mechanical Isolation = structural differences in reproductive organs can prevent copulation. Square Peg/Round Hole ?

  35. REPRODUCTIVE ISOLATING MECHAMISMS: Prevention of Fertilization Shapes of floral features in plants can affect the transfer of pollen is also an example of mechanical isolation The pink lady’s slipper orchid exhibits a mechanical isolating mechanism This orchid looks like a wasp

  36. REPRODUCTIVE ISOLATING MECHAMISMS: Gametic Isolation • In coral reefs, many species release sperm & eggs into the water at the same time. • Sperm & egg of the SAME species recognize each other by molecular markers • In many species sperm cannot survive inside the female Coral spawning a cloud of sperm

  37. REPRODUCTIVE ISOLATING MECHAMISMS:Post Zygotic mechanisms preventing hybrids from mating Prevents maturation & reproduction in offspring from interspecies reproduction A spotted mule is sterile, resulting from horse & donkey mating Hybrid trilliums are sterile

  38. REPRODUCTIVE ISOLATING MECHAMISMS:Post Zygotic Isolating Mechanisms • Zygote mortality & Hybrid inviability ensure reproductive isolation of a gene pool by preventing the exchange of alleles between the parent species

  39. MODES OF SPECIATION 1. Allopatric Speciation is the evolution of populations into separate species as a result of geographic isolation The canyon is a barrier to dispersal by small mammals, (Grand Canyon Squirrels) and as a consequence the isolated populations can diverge.

  40. Mountain range is the barrier

  41. MODES OF SPECIATION 2. Sympatric Speciation is the evolution of populations within the same geographic area into separate species. Largely due to genetic drift. Good Bye Chapter 12 Evidence suggests stickleback fish species evolved by sympatric speciation

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