Population Genetics (Learning Objectives) • Define the terms population, species, allelic and genotypic frequencies, gene pool, and fixed allele, genetic drift, bottle-neck effect, founder effect. • Explain the difference between microevolution and macroevolution. • Review how genotypic and allelic frequencies are calculated. Given the appropriate information about a population you should be able to calculate the genotypic and allelic frequencies of homozygous dominant, recessive, or heterozygous individuals (following the example discussed in class). • Visit this website to learn the factors that lead to changes in genotypic and allelic frequencies between generations: http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6- OSU.swf • What is the Hardy-Weinberg Equilibrium and what are its conditions. • What are the factors that lead to microevolution? • What is the source of new alleles within any population?
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Population Genetics (Learning Objectives)
• Define the terms population, species, allelic and genotypic frequencies, gene pool, and fixed allele, genetic drift, bottle-neck effect, founder effect.
• Explain the difference between microevolution and macroevolution.• Review how genotypic and allelic frequencies are calculated.
Given the appropriate information about a population you should be able to calculate the genotypic and allelic frequencies of homozygous dominant, recessive, or heterozygous individuals (following the example discussed in class).
• Visit this website to learn the factors that lead to changes in genotypic and allelic frequencies between generations: http://zoology.okstate.edu/zoo_lrc/biol1114/tutorials/Flash/life4e_15-6-OSU.swf
• What is the Hardy-Weinberg Equilibrium and what are its conditions.• What are the factors that lead to microevolution?• What is the source of new alleles within any population?
p = allele frequency of one alleleq = allele frequency of a second allele
p2 + 2pq + q2 = 1
p2 and q2 Frequencies for each homozygote
2pq Frequency for heterozygotes
All of the allele frequencies together equals 1
All of the genotype frequencies together equals 1
Hardy-Weinberg Equation
Populations at Hardy-Weinberg equilibrium must satisfy five conditions.(1) Very large population size. In small populations,
chance fluctuations in the gene pool, genetic drift, can cause genotype frequencies to change over time.
(2) No migrations. Gene flow, the transfer of alleles due to the movement of individuals or gametes into or out of our target population can change the proportions of alleles.
(3) No net mutations. If one allele can mutate into another, the gene pool will be altered.
(4) Random mating. If individuals pick mates with certain genotypes, then the mixing of gametes will not be random and the Hardy-Weinberg equilibrium does not occur.
(5) No natural selection. If there is differential survival or mating success among genotypes, then the frequencies of alleles in the next variation will deviate from the frequencies predicted by the Hardy-Weinberg equation.
Evolution results when any of these five conditions are not met - when a population experiences deviations from the stability predicted by the Hardy-Weinberg theory.
Genetic Driftchanges allelic frequencies in populations
The bottleneck effect
The founder effect
Caused by four factors:1. Non-Random mating2. Genetic drift – due to sampling/ bottleneck &
founder effects, geographic & cultural separation
3. Migration- of fertile individuals4. Mutation- in germline cells transmitted in
gamete5. Natural selection- accumulates and maintains
favorable genotypes in a population
Microevolution
Figure 14.3
Source of the Hardy-Weinberg Equation
Figure 14.3
Solving a Problem
Figure 14.4
Solving a Problem
Figure 14.4
Figure 14.3
Calculating the Carrier Frequency of an Autosomal Recessive
Figure 14.5
Table 14.3
Calculating the Carrier Frequency of an Autosomal Recessive
Figure 14.3
Calculating the Carrier Frequency of an Autosomal Recessive
What is the probability that two unrelated Caucasians will have an affected child?
Probability that both are carriers =1/23 x 1/23 = 1/529
Probability that their child has CF = 1/4 Therefore, probability = 1/529 x 1/4 =
1/2,116
Calculation of % PKU carriers from screening
About 1 in 10,000 babies in US are born with PKU- The frequency of homozygous recessive individuals = q2 = 1
in 10,000 or 0.0001.- The frequency of the recessive allele (q) is the square root
of 0.0001 = 0.01.- The frequency of the dominant allele (p) is p = 1 - q or 1 -
0.01 = 0.99.The frequency of carriers (heterozygous individuals) is
2pq = 2 x 0.99 x 0.01 = 0.0198 or about 2%.About 2% of the U.S. population carries the PKU allele.
Question
What is the chance or probability that two unrelated white Caucasian US individuals will have an affected child?
Calculating the Risk withX-linked Traits
• For females, the standard Hardy-Weinberg equation applies
p2 + 2pq + q2 = 1
• However, in males the allele frequency is the phenotypic frequency
p + q = 1
Calculating the Risk withX-linked Traits
Figure 14.6 30
Calculating the Risk withX-linked Traits
Hardy-Weinberg Equilibrium
• Rare for protein-encoding genes that affect the phenotype
• Applies to portions of the genome that do not affect phenotype
• Includes repeated DNA segments– Not subject to natural selection
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DNA Repeats
• Short repeated segments are distributed all over the genome
• Repeat numbers can be considered alleles and used to classify individuals
• Types– Variable number of tandem repeats
(VNTRs)– Short tandem repeats (STRs)
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DNA Repeats
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DNA Profiling
• Developed in the 1980s by British geneticist Sir Alec Jeffreys
• Also called DNA fingerprinting• Identifies individuals• Used in forensics, agriculture, paternity
testing, and historical investigations• http://highered.mheducation.com/sites/dl/free/007283512