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EVOLUTION OF POPULATIONS. YOU MUST KNOW… HOW MUTATION AND SEXUAL REPRODUCTION EACH PRODUCE GENETIC VARIATION THE CONDITIONS FOR HARDY- WEINBERG EQUILIBRIUM.

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Presentation on theme: "EVOLUTION OF POPULATIONS. YOU MUST KNOW… HOW MUTATION AND SEXUAL REPRODUCTION EACH PRODUCE GENETIC VARIATION THE CONDITIONS FOR HARDY- WEINBERG EQUILIBRIUM."— Presentation transcript:

1 EVOLUTION OF POPULATIONS

2 YOU MUST KNOW… HOW MUTATION AND SEXUAL REPRODUCTION EACH PRODUCE GENETIC VARIATION THE CONDITIONS FOR HARDY- WEINBERG EQUILIBRIUM HOW TO USE THE HARDY-WEINBERG EQUATION TO CALCULATE ALLELIC FREQUENCIES AND TO TEST WHETHER A POPULATION IS EVOLVING

3 CONCEPT 23.1 MUTATION AND SEXUAL REPRODUCTION PRODUCE THE GENETIC VARIATION THAT MAKES EVOLUTION POSSIBLE

4 MICROEVOLUTION – CHANGE IN THE ALLELE FREQUENCIES OF A POPULATION OVER GENERATIONS (EVOLUTION ON A SMALL SCALE) MUTATIONS – THE ONLY SOURCE OF NEW GENES AND NEW ALLELES POINT MUTATIONS – CHANGES IN ONE BASE IN A GENE EX. SICKLE-CELL DISEASE CHROMOSOMAL MUTATIONS – DELETE, DISRUPT, DUPLICATE, OR REARRANGE MANY LOCI AT ONCE (USUALLY HARMFUL BUT NOT ALWAYS)

5 HBB: The Gene Associated with Sickle Cell Anemia Locus: 11p The HBB gene is found in region 15.5 on the short (p) arm of human chromosome 11. Protein Function: Hemoglobin molecules, which reside in red blood cells, are responsible for carrying oxygen from the lungs to various parts of the body for use in respiration. The HBB gene codes for one of the two types of polypeptide chains found in adult hemoglobin.

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7 MOST GENETIC VARIATIONS ARE DUE TO THE SEXUAL RECOMBINATION OF ALLELES THAT ALREADY EXIST IN A POPULATION CROSSING OVER – DURING PROPHASE I OF MEIOSIS INDEPENDENT ASSORTMENT OF CHROMOSOMES DURING MEIOSIS FERTILIZATION (2 23 x 2 23 DIFFERENT COMBINATIONS FOR HUMAN SPERM AND EGG)

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9 CONCEPT 23.2 THE HARDY- WEINBERG EQUATION CAN BE USED TO TEST WHETHER A POPULATION IS EVOLVING

10 POPULATION – A GROUP OF INDIVIDUALS OF THE SAME SPECIES GENE POOL – ALL THE ALLELES AT ALL LOCI IN ALL THE MEMBERS OF A POPULATION IF ALL MEMBERS OF A POPULATION ARE HOMOZYGOUS FOR THE SAME ALLELE, THE ALLELE IS FIXED ONLY ONE ALLELE EXISTS AT THAT PARTICULAR LOCUS IN THE POPULATION

11 THE GREATER THE NUMBER OF FIXED ALLELES, THE LOWER THE SPECIES DIVERSITY THE HARDY-WEINBERG THEOREM DESCRIBES A POPULATION THAT IS NOT EVOLVING THE FREQUENCIES OF ALLELES AND GENES IN A POPULATIONS GENE POOL WILL REMAIN CONSTANT OVER THE COURSE OF GENERATIONS UNLESS THEY ARE ACTED UPON BY FORCES OTHER THAN MENDELIAN SEGREGATION AND THE RECOMBINATION OF ALLELES

12 5 CONDITIONS FOR HARDY- WEINBERG EQUILIBRIUM NO MUTATIONS RANDOM MATING NO NATURAL SELECTION THE POPULATION SIZE MUST BE EXTREMELY LARGE (NO GENETIC DRIFT) NO GENE FLOW (IMMIGRATION, TRANSFER OF POLLEN)

13 IT IS UNLIKELY THAT ALL THE CONDITIONS FOR HARDY-WEINBERG EQUILIBRIUM WILL BE MET ALLELIC FREQUENCIES CHANGE AND POPULATIONS EVOLVE p = dominant allele (R) q = recessive allele (r) p 2 + 2pq + q 2 = 1

14 CONCEPT 23.3 NATURAL SELECTION, GENETIC DRIFT, AND GENE FLOW CAN ALTER ALLELE FREQUENCIES IN A POPULATION (ALTHOUGH MUTATIONS DO TOO)

15 3 MAJOR FACTORS ALTER ALLELIC FREQUENCIES AND BRING EVOLUTIONARY CHANGES 1.NATURAL SELECTION 2.GENETIC DRIFT 3.GENE FLOW

16 NATURAL SELECTION RESULTS IN ALLELES BEING PASSED TO THE NEXT GENERATION IN PROPORTIONS DIFFERENT FROM THEIR RELATIVE FREQUENCIES IN THE PRESENT GENERATION STRONGER INDIVIDUALS TEND TO PRODUCE MORE OFFSPRING

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18 GENETIC DRIFT UNPREDICTABLE FLUCTUATION IN ALLELIC FREQUENCIES FROM ONE GENERATION TO THE NEXT THE SMALLER THE POPULATION, THE GREATER THE CHANCE IS FOR GENETIC DRIFT IS A RANDOM, NONADAPTIVE CHANGE IN ALLELIC FREQUENCIES

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20 FOUNDER EFFECT – A FEW INDIVIDUALS BECOME ISOLATED FROM A LARGER POPULATION AND ESTABLISH A NEW POPULATION WHOSE GENE POOL IS NOT REFLECTIVE OF THE SOURCE POPULATION BOTTLENECK EFFECT – A SUDDEN CHANGE IN THE ENVT. DRASTICALLY REDUCES THE SIZE OF A POPULATION THE FEW SURVIVORS MAY HAVE A GENE POOL THAT NO LONGER REFLECTS THE ORIGINAL POPULATIONS GENE POOL

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22 GENE FLOW OCCURS WHEN A POPULATION GAINS OR LOSES ALLELES BY GENETIC ADDITIONS TO AND/OR SUBTRACTIONS FROM THE POPULATION (aka MIGRATION) A RESULT OF THE MOVEMENT OF FERTILE INDIVIDUALS OR GAMETES TENDS TO REDUCE THE GENETIC DIFFERENCES BETWEEN POPULATIONS

23 CONCEPT 23.4 NATURAL SELECTION IS THE ONLY MECHANISM THAT CONSISTENTLY CAUSES ADAPTIVE EVOLUTION

24 RELATIVE FITNESS REFERS TO THE CONTRIBUTION AN ORGANISM MAKES TO THE GENE POOL OF THE NEXT GENERATION RELATIVE TO THE CONTRIBUTIONS OF OTHER MEMBERS IT IS MEASURED ONLY BY REPRODUCTIVE SUCCESS

25 NATURAL SELECTION ACTS MORE DIRECTLY ON PHENOTYPE AND INDIRECTLY ON THE GENOTYPE AND CAN ALTER THE FREQUENCY DISTRIBUTION OF HERITABLE TRAITS IN 3 WAYS DIRECTIONAL SELECTION DISRUPTIVE SELECTION STABILIZING SELECTION

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27 DIRECTIONAL SELECTION INDIVIDUALS WITH ONE EXTREME OF A PHENOTYPIC RANGE ARE FAVORED, SHIFTING THE CURVE TOWARD THIS EXTREME

28 DISRUPTIVE SELECTION OCCURS WHEN CONDITIONS FAVOR INDIVIDUALS ON BOTH EXTREMES OF A PHENOTYPIC RANGE RATHER THAN INDIVIDUALS WITH INTERMEDIATE PHENOTYPES

29 STABILIZING SELECTION ACTS AGAINST BOTH EXTREME PHENOTYPES AND FAVORS INTERMEDIATE VARIANTS

30 GENETIC VARIATION IS PRESERVED IN A POPULATION BY: DIPLOIDY – ORGANISMS ARE CAPABLE OF HIDING GENETIC VARIATION FROM SELECTION HETEROZYGOTE ADVANTAGE – INDIVIDUALS HAVE AN ADVANTAGE FOR SURVIVAL EX. SICKLE-CELL DISEASE


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