Post on 22-Dec-2015
Constant Allele Frequencies
Hardy-Weinberg Equilibrium
Population An interbreeding group of the same species
within a given geographical area Gene pool
the collection of all alleles in the members of the population
Population genetics the study of the genetics of a population and how the
alleles vary with time Gene Flow
alleles can move between populations when individuals migrate and mate
Allele Frequencies
Allelic # of particular allele
Frequency total # of alleles in the population
Count both chromosomes of each individual Allele frequencies affect the genotype
frequencies The frequency of each type of
homozygote and heterozygote in the population
Phenotype Frequencies Frequency of a trait varies in different populations
Table 14.1
Microevolution and Macroevolution Microevolution
Genetic change due to changing allelic frequencies in populations
Macroevolution The formation of new species
Allelic frequencies can change when there is:
Nonrandom mating Individuals of one genotype are more likely to
produce offspring with each other than with those of other genotypes
Gene flow e.g. migration
Genetic drift Reproductively isolated groups form within or
separate from a larger population Mutation
Introduces new alleles into the population Natural selection
Individuals with a particular genotype are more likely to produce viable offspring
Hardy-Weinberg Equilibrium
Developed by mathematicians A condition in which allele frequencies
remain constant Used algebra to explain how allele
frequencies predicts genotype and phenotype frequencies in equilibrium
Hardy-Weinberg Equilibrium
p + q = 1All of the allele frequencies together equals 1 or the whole collection of alleles
p = allele frequency of one allele (e.g. dominant)
q = allele frequency of a second allele (e.g. recessive)
p2 + 2pq + q2 = 1All of the genotype frequencies together equals 1
p2 and q2 =genotype frequencies for each homozygote
2pq = genotype frequency for heterozygotes
2 possible combinations (p egg + q sperm or vice versa)
Figure 14.3
Table 14.2
Applying Hardy-Weinberg Equilibrium
Used to determine carrier probability
Homozygous recessive used to determine frequency of allele in population (phenotype is genotype)
Applying Hardy-Weinberg Equilibrium: Cystic Fibrosis
Calculating Carrier Frequency for X-linked Traits
Figure 14.6
DNA Profiling (a.k.a. DNA Fingerprinting
Hardy-Weinberg equilibrium applies to portions of the genome that do not affect phenotype They are not subject to natural selection Short repeated segments that are not protein encoding,
distributed all over the genome Detects differences in repeat copy number Calculates probability that certain combinations can
occur in two sources of DNA Requires molecular techniques and population studies
Preparing DNA for Profiling –Restriction Enzymes
Chop up the DNA at specific sequences using “restriction enzymes”
Creates RFLPs Restriction fragment length polymorphisms
Preparing DNA for Profiling –Running a Gel
Run samples on an agarose or polyacrylamide gel DNA has a negative charge so it will travel
toward a positive charge Larger fragments will not move as far through
the gel
DNA Profiling
Developed in 1980s Identifies individuals Used in forensics, agriculture, paternity
testing, and historical investigations DNA can be obtained from many sources
DNA Profiles
Figure 14.9
DNA Profiling
Types of repeats Variable number tandem repeats
(VNTRs) Short tandem repeats (STRs)
Shorter than VNTRs Useful if DNA from sample is fragmented
or degraded mtDNA
Useful if nuclear DNA is highly damaged
A Sneeze Identifies Art Thief
Table 14.6
Comparing DNA Sequences
Figure 14.10
Figure 14.10