population_genetics

population_genetics - Causes of mutations 1. Ionizing...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Causes of mutations 1. Ionizing radiation 2. Chemical mutagens 3. Spontaneous mutations during DNA replication. Mutation rates Achondroplastic Dwarfism Total color Blindness Hemophilia B Hemophilia A Most genes Rates/million 40 to 120 30 20 to 40 5 to 10 1 1 gamete in 10 carries a new mutant! Effects of mutations 1. Harmful: 1. Lethal Not expressed except as Minor major aa No effect = Neutral mutation = same fitness Mutation in non-functional DNA Silent mutation mutation for equivalent code-on or equivalent group of amino acids Mutated gene expressed but the same fitness within the environment blue or brown eyes Most mutations recessive 3. Beneficial = increases the fitness of an organism Mutations and Evolution 1. Mutations determine survival and reproduction Fitness positive fitness negative fitness neutral fitness = = = Fitness Fitness no change in fitness 2. Most mutations have negative fitness. 3.Mutations are random i.e. not directed by environment Today's view Mutation provides the variability new alleles Sexual and genetic recombination (cross over) provide variability by reshuffling existing alleles Natural selection acts on the alleles present in the population causing shifts in their frequency of occurrence Acquired characteristics cannot be passed on via DNA to the next generation. i.e. The environment can't change the DNA This doesn't happen Inheritance of Acquired Characteristics ENVIRONMENT USE & DISUSE "NEED" HEREDITY NEW SPECIES This does happen Natural Selection MUTATION CROSSOVER Genetic recombination SEX Fertilization HEREDITY NATURAL SELECTION VARIATION NEW SPECIES To measure the rate of evolution Molecular Clocks 1. If mutation is fairly constant the # of nucleotide differences between species indicate the time that the species have been separated 2. Best to examine non-coding regions of the codon 3. Nucleotide sequences vary in rate of evolution; best to use several nucleotide sites and average the rate of change But you need to know the average rate of mutation Primate EvolutionMolecular Clock Conclusion? Data strongly support the hypothesis of evolution All organisms share a common ancestor! Let's Leave This Subject For Awhile POPULATION GENETICS POPULATION GENETICS= Study of the change in the allele frequency in a population through time Gene pool = total collection of the alleles of a gene in the population Rabbit Island 1000 rabbits = 600 brown & 400 white 2 alleles & complete dominance Brown (B) dominant White (b) recessive 3 genotypes BB & Bb= Brown bb = white Suppose 500 Homozygous brown rabbits BB = 1000 B alleles 100 Heterozygous brown rabbits Bb = 100 B alleles 100 b alleles 400 Homozygous white rabbits bb = 800 b alleles Total: 1100 B alleles 900 b alleles p = fraction of gene pool with dominant allele. (p= .55) q = fraction of gene pool with recessive allele. (q= .45) Total p + q = 1.00 (0.55) + (0.45) = 1.00 Suppose the Allele Frequency in the Original Colonists was Imagine a barrel with 55% brown marbles and 45% white. What are the chances of drawing two B's from the population at random? A)0.55 B)0.45 C)0.3025 D)0.4950 E)None of the above GENOTYPES in the NEXT GENERATION The frequency of drawing the BB genotype in the next generation is C) 0.3025 P2 = (0.55)2 = 0.3025 or about 30% i.e. What are the chances of drawing two b's from the gene pool if there are 55% brown and 45% white alleles? A) 0.55 B) 0.45 C) 0. 3025 D) 0. 4950 E) None of the above What is the frequency of the white genotype in the next generation? What is the frequency of the white genotype? Answer: E) None of the above q2 = (0.45)2 = 0.2025 or about 20% What is the frequency of the Bb genotype in the next population? A) 0.55 B) 0.45 C) 0.3025 D) 0.4950 E) None of the above What is the frequency of the Bb genotype? Answer: D) 0.4950 2 (pq) = 2 (0.55 x 0.45)= 0.4950 or about 50% HardyWeinberg Principle p + 2pq + q = 1.0 BB Bb bb 2 2 HARDYWEINBERG PRICIPLE Allele frequency & genotype frequency will remain constant from generation to generation if 1. No natural selection 2. No differential migration (no gene flow) 3. No mutation 4. Random mating 5. Large population (no genetic drift or random genetic changes) HardyWeinberg Principle p + 2pq + q = 1.0 BB Bb bb 2 2 If a change in allele frequency does occur (i.e. there is evolution), then the rules of the Hardy Weinberg Principle have been violated. Consider the problem of population size Random changes will be important in small populations (< 500 individuals). Small populations do not have a large number of possible variations in their alleles. 1. "Founder effect" during the founding of new colonies. 2. "Bottleneck effect" because of population crashes. 3. "Genetic drift" in small populations Using the HardyWeinberg equation How many of you can roll your tongues? It is due to a dominant allele R She is either RR or Rr Nonrollers are rr Suppose 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) What is the frequency of nontongue rollers (rr) in the population? A) 0.36 B) 0.64 C) 0.8 D) None of the above E) I don't know how to do this So 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) Let us assume that there is no selective advantage to tongue rolling so that the HardyWeinberg conditions hold Now remembering that the gene pool is composed of only R's & r's, can you calculate what % of the gene pool is r and what % is R? Clicker Question A) B) C) D) E) If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) What is the frequency of the allele for tongue rolling (r) in the gene pool? 0.2 0.36 0.6 0.8 I don't know how to do this Clicker Question A) B) C) D) E) If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) What is the frequency of the allele for tongue rolling (R) in the gene pool? 0.2 0.36 0.6 0.8 I don't know how to do this A) B) C) D) E) If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) What is the % of homozygous dominants (RR) in the population? 4% 16% 32% 35% None of the above Clicker Question A) B) C) D) E) If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) What is the % of heterozygotes (Rr) in the population? 4% 16% 32% 35% None of the above Clicker Question If 36% of the class can roll their tongues (RR or Rr) & 64% can not roll their tongues (rr) ANSWER Remember p2 + 2pq + q2 RR + (Rr + rR) + rr 4% + 32% + 64% = 100% Now you know how to do it. Don't you? First, figure out the recessive allele frequency and everything else follows! LECTURE'S OVER! I HOPE YOU DID WELL ON THE EXAM! ou Y d it, sai Doc ...
View Full Document

Ask a homework question - tutors are online