Chapter 19 Systems, Equilibrium, and Change

Population Genetics

• The study of the frequency, distribution, and inheritance of alleles in a populations

Evolution

Change in population over time through changes in the genome

• Changes to a population’s DNA over time, that gets passed on to future generations

Phenotype Frequency

The proportion of a population with a particular phenotype

Genotype Frequency

The proportion of a population with a particular genotype

Allele Frequency

The proportion of a particular allele in a gene pool of a population for a given gene

Hardy-Weinberg Principle

• Used to predict allele frequencies in a population, when we don’t know the genotype of all individuals

• Gene pool doesn’t change overtime

• Frequency stays the same

p

The frequency of the Dominant allele

q

The frequency of the Recessive allele

p²

The frequency of Homozygous dominant

q²

The frequency of Homozygous recessive

2pq

The frequency of Heterozygous

5 Conditions that must be met for a population to be in equilibrium

• No net mutations

• No migration (gene flow)

• random mating

• Large population size- chance events will not alter allele frequencies

• No Natural selection

If population is showing changes to its allele frequencies over a period of time, this could indicate evolution.

Population Genetics (Population)

Group of organisms that is of the same species, living in the same are at the same time

Population Genetics (Genes)

The basic unit of heredity carried on chromosomes and control the inheritance of traits

Population Genetics (Allele)

Different form of the same genes

Population Genetics (Gene Pool)

The sum of all the alleles for all the genes in a population

Heritable Mutations

• DNA changes in an individual; which increases genetic diversity

• It may affect the entire gene pool

• May be helpful and or harmful depending on the environment

Gene Flow (Migration)

The net movement of alleles from one population to another due to the migration of individuals

• Migration: INCREASES genetic diversity

• Emigration: DECREASES genetic diversity

Non-Random Mating

• Will increase or decrease the probability that a specific individual will mate

• Also known as “sexual selection” or “artificial selection” due to preferred phenotypes, inbreeding

• Decrease genetic diversity

Genetic Drift

• Changes in allele Frequencies in small populations due to a chance event

• Usually result in the disappearance of particular genes (decrease diversity)

Founder Effect (genetic drift)

Gene pool change when a new colony is started by a few members of the original population ( starting with only a few of the possible alleles)

• Reduced genetic variation from the original

• Non-random sample of genes from the original population

Bottleneck Effect (Genetic drift)

Gene pool change that occurs due to a rapid decrease in population size

• Only a few individuals survive, and pass their reduced number of genes onto the new population

Natural selection

In a given environment, some individuals are better able to survive and reproduce (pass on their genes) than others

• Selective advantage

  • It is the environment that determines if a mutation is helpful, harmful, or neutral

  • If a population lacks genetic diversity, it will be less able to adapt to environment changes