Population Genetics

Population

Any group of members of the same species in a given geographical area who are potentially capable of mating and producing fertile offspring.

Population genetics

The study of allele frequencies in groups of organisms of the same species in the same geographic area.

Frequencies

How often a particular gene variant occurs in a particular population.

Phenotypes

The number of individuals in a population that have a specific observable trait.

Genotypes

The percentage of individuals in a population that have a specific genotype.

Alleles

The percentage of all copies of a certain gene in a population that carry a specific allele.

Genotype Frequencies

Nonrandom mating, migrate, genetic drift, mutation, and natural selection.

Nonrandom mating

Individuals of one genotype are more likely to produce offspring with each other than with those of other genotypes

Genetic Drift

Reproductively isolated small groups form within or separate from a larger population

Mutation

Introduces new alleles into a population.

Natural Selection

People with a particular genotype are more likely to produce viable, fertile offspring under a specific environmental condition than individuals with other genotypes.

Allele Frequencies

The term used to describe the fraction of gene copies that are of a particular allele in a defined population.

Gene Frequency

Allele Frequency

Microevolution

Shifting allele frequencies in populations reflect small steps of genetic change.

Genetic Equilibrium

When allele frequencies are not changing, is rare. Because of the factors that change genotype frequencies, Microevolution is not only possible, but also nearly unavoidable.

Macroevolutionary Changes

Accumulate to keep two fertile organisms of opposite sex in a population from successfully producing fertile offspring together has occured

Macroevolution

The formation of new species.

Hardy - Weinberg Equilibrium

Unusual situation in which certain allele frequencies stay constant.

Hardy and Weinberg

Independently used algebra to explain how allele frequencies can be used to predict phenotypic and genotypic frequencies in populations of diploid, sexually reproducing organisms.

Hardy and Weinberg

Disproved the assumption that dominant traits increase while recessive traits decrease using the language of algebra.

p + q = 1.0

The expression of population genetics in algebraic terms begins with the simple equation.

Hardy-Weinberg model

Describes and predicts a balanced equilibrium in the frequencies of alleles and genotypes within a freely interbreeding population, assuming a large population size, no mutation, no genetic drift, no natural selection, no gene flow between populations, and random mating patterns

DNA Profiling

DNA Fingerprinting, DNA Testing, DNA Typing, Genetic Fingerprinting, Genotyping, and Identity Testing.

DNA Profiling

The process of DNA fingerprinting was invented by Sir Alec Jeffreys at the University of Leicester in 1985. He was knighted in 1994 for his contributions in Science and Technology

Sir Alec Jeffreys

The process of DNA fingerprinting was invented at the University of Leicester in 1985.

Tommie Lee Andrew

In 1988, Jeffreys’ approach matched DNA profiles from a suspect’s blood cells to sperm cells left on his victim in a notorious rape case.

DNA Profiling

Uses repetitive sequences that are highly variable, called variable number tandem repeats (VNTRs), and short tandem repeats (STRs).

VNTR

A location in a genome where a short nucleotide sequence is organized as a tandem repeat.

Minisatellites

VNTRs

Microsatellites

STRs

STR

A type of repetitive sequence used in DNA profiling.

Mitochondrial DNA (mtDNA)

Used when DNA is extremely damaged, particularly two regions of repeats that are highly variable in populations.

Tommie Lee Andrews

Suspect in a notorious rape case where DNA profiles matched his blood cells to sperm cells left on the victim.

DNA sources

Common sources of DNA include cells in hair, blood, skin, secretions, or the inside of the cheek.

Population data analysis

Statistical analysis required to interpret DNA profiles.

Variable Number Tandem Repeats (VNTRs)

Highly variable repetitive sequences used in DNA profiling to distinguish individuals.

Fragmented DNA

DNA that is broken into smaller pieces, often requiring the use of STRs for profiling.

Monozygotic twins

Individuals that share 99.9% of their DNA sequences, making them indistinguishable by DNA profiling.

Genetic relatedness

Degree of similarity between DNA sequences, often assessed using VNTR analysis.

Allele

Each variant acts as an inherited allele, allowing them to be used for personal or parental identification.

DNA Profiling

The process of detecting differing numbers of repeats at specific chromosomal loci to identify individuals.

Heterozygote

An individual with different alleles at a particular chromosomal locus.

Homozygote

An individual with the same number of repeats on the two copies of the chromosome at a particular chromosomal locus.

Reference Sample

A sample of an individual's DNA used in DNA profiling, typically collected via a buccal swab.

Buccal Swab

The most desirable method of collecting a reference sample to reduce contamination.

DNA Profiling Methods

Techniques used in DNA profiling, including Electrophoresis, Polymerase Chain Reaction (PCR), Restriction Fragment Length Polymorphism (RFLP), Random Amplified Polymorphic DNA (RAPD), and Amplified Fragment Length Polymorphism (AFLP).

Electrophoresis

A separation technique based on the mobility of ions in an electric field, where ions migrate towards electrodes depending on their charge.

Positively Charged Ions

Ions migrate towards a negative electrode.

Negatively Charged Ions

Migrate toward a positive electrode.

Polymerase Chain Reaction (PCR)

A common laboratory technique used to make many copies (millions or billions!) of a particular region of DNA. It is to make enough of the target DNA region that it can be analyzed or used in some other way. For instance, DNA amplified by PCR may be sent for sequencing, visualized by gel electrophoresis, or cloned into a plasmid for further experiments

Taq Polymerase

A thermostable DNA polymerase used in PCR.

Restriction Fragment Length Polymorphism (RFLP)

A technique that analyzes the length of DNA strands with repeating base pair patterns by fragmenting DNA with a restriction enzyme.

Random Amplified Polymorphic DNA

It is a type of PCR reaction, but the segments of DNA that are amplified at random.

Amplified Fragment Length Polymorphism

This technique is also faster than RFLP analysis and used PCR to amplify DNA samples. It relied on variable number tandem repeat (VNTR) polymorphisms to distinguish various alleles, which were separated on a polyacrylamide gel.

Restriction Digest

The process of fragmenting a sample of DNA by a restriction enzyme that recognizes and cuts DNA at specific short sequences.

Agarose Gel Electrophoresis

A process used to separate DNA fragments by length after they have been fragmented.

Southern Blot Procedure

A method used to transfer DNA fragments from agarose gel to a membrane for further analysis.

Hybridization

The process of binding a labeled DNA probe to a membrane to determine the length of complementary DNA fragments.

DNA Primer

Short sequences of nucleotides designed specifically for the DNA region of interest in PCR.

Target DNA Region

The specific region of DNA that is amplified during PCR.

Fragment Length

The length of DNA fragments that can vary between individuals, each considered an allele.

Labeled DNA Probe

A DNA sequence used to detect specific fragments of DNA through hybridization.

Genetic Analysis

The study of genetic variations, such as those detected through RFLPs.

VNTR polymorphisms

Variable number tandem repeat polymorphisms used to distinguish various alleles in DNA profiling.

Polyacrylamide gel

A medium used to separate alleles in the analysis phase of Amplified Fragment Length Polymorphism.

Applications of DNA Profiling

Includes diagnosis and developing cures for inherited disorders, biological evidence to identify criminals, paternity disputes, personal identification, identifying natural disaster victims, and identifying an individual's DNA in mixtures.

Nonrandom Mating

Occurs when the probability that two individuals in a population will mate is not the same for all possible pairs of individuals.

Inbreeding

Individuals are more likely to mate with close relatives than with distant relatives.

Outbreeding

Individuals are more likely to mate with distant relatives than with close relatives.

Genotype frequencies

Inbreeding changes these frequencies, increasing homozygotes and decreasing heterozygotes.

Selfing

An extreme case of inbreeding where individuals self

Coefficient of inbreeding (F)

A measure where F=0 indicates random mating, F=.5 indicates all reproduction by self

Migration

In an evolutionary sense, the movement of alleles between populations as organisms disperse from population to population.

Gene flow

Synonymous with migration; refers to the movement of alleles between populations.

Effects of migration on allele frequencies

In absence of selection, migration homogenizes allele frequencies among populations; if selection and migration increase the same alleles, selection amplifies migration's effect.

Selection vs. migration

If selection is stronger than migration, differences among populations will be maintained, even in the face of migration.

Avoiding inbreeding

Can be achieved through dispersal, which may also diminish sibling competition.

Genetic Drift

Change in allele frequencies in a population from generation to generation that occurs due to chance events.

Sampling Error

The error that occurs in selecting the alleles for the next generation from the gene pool of the current generation.

Bottleneck Effect

An extreme example of genetic drift that happens when the size of a population is severely reduced due to events like natural disasters.

Founder Effect

An extreme example of genetic drift that occurs when a small group of individuals breaks off from a larger population to establish a colony.

Mutation

A change in the DNA at a particular locus in an organism, which is a weak force for changing allele frequencies but a strong force for introducing new alleles.

Genetic Load

The collection of deleterious alleles in a population.

Natural Selection

Out of all the mechanisms of evolution, this is the only one that can consistently make populations adapted, or better-suited for their environment, over time as fitness increasing alleles becoming more common in the population over generations.

Fitness

A measure of relative reproductive success, referring to how many offspring organisms of a particular genotype or phenotype leave in the next generation.

Polygenic Traits

Traits determined by many genes, often forming a bell curve distribution in a population.

Stabilizing Selection

Intermediate phenotypes have the highest fitness, and the bell curve tends to narrow

Directional Selection

One of the extreme phenotypes has the highest fitness. The bell curve shifts towards the more fit phenotype

Disruptive Selection

Both extreme phenotypes have a higher fitness than intermediate phenotypes. The bell curve develops two peaks.

Eugenics

The control of individual reproduction to serve a societal goal.

Positive Eugenics

Encourages those deemed acceptable or superior to reproduce.

Negative Eugenics

Restricts reproduction of those considered inferior.

Genetic Technology

Aspects of technology that affect reproductive choices and allele frequencies, aimed at alleviating or preventing suffering.

Microevolution

The process of evolution that occurs on a small scale, such as changes in allele frequencies within a population.

Alleles

Different versions of a gene that can exist at a specific locus.

Phenotype

Observable features of an organism that are influenced by its genotype.

Genotype

The genetic constitution of an organism, which determines its traits.

Natural Selection Mechanisms

The processes through which natural selection can act on traits, including stabilizing, directional, and disruptive selection.

Catastrophe

An event that can lead to a bottleneck effect by severely reducing population size.

Colonization

The process through which a small group establishes a new colony, leading to the founder effect.