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