Bio unit 1 exam

Genotype frequency

(Number of individuals that have a genotype) / (total number of individuals in the population )

Allele frequency

(number of copies of an allele) / (Total number of of alleles in a population)

Evolution

Change in the genetic makeup of a population over generations

Natural Selection

“Variants within populations that can be inherited and that are best suited for growth and reproduction in given environment

Environmental Variants

(sub category from natural selection) due to differences in the environment

Genetic Variations

(Sub category from natural selection) Due to differences in the genetic material that is transmitted from parent to offspring

Mutations

Arise either from random errors during DNA replication or from environment factors that can damage DNA

Evolution Theory

Understanding of how evolution works based on many observations and experiments

Example of evolution theory

Closely related species are likely to resemble each other more closely than they do more distantly related species

Phenotype variation

Differences in observable traits among individuals of our species

Species

group of individuals that are capable, through reproduction, of sharing alleles with one another

Gene pool

Consists of al the alleles present in all of the individuals in the species

Population Genetics

Study of genetic variation in natural populations

Somatic mutations

Occurs in bodies tissues in non-reproductive cell; only affects only the cell descended from the one cell in which the mutation originally arose - not passed on to the next generation

Germ-line mutation

Present in sperm or egg, are evolutionary important because they are passed on to the next generation and appear in every cell of an offspring

how to determine evolution has occured

If allele frequencies change or if genotype frequencies change over a generation

Hardy-Weinberg equilibrium

Describes what we expect at a gene (locus) when evolution is NOT occuring - baseline expectation for a non-evolving population

5 things that are said to be Hardy - Weinberg equilibrium as these are meat

1. No selection: no differences in the survival and reproductive success

2. No mutations: No mutations within gene

3. No migration: Population size is not changed by movement of individuals

4. Large population ( No genetic drift): Sufficiently large to prevent sampling errors

5. Random mating: Individuals in the population mate at random

Natural Selection occurs when these observations are met

1. There is variation in the population

2. When the variation is heritable

3. resources must be finite driving competition among individuals

4. As a result of competition, mortality occurs

evolution by natural selection

Leaving more offsprings with a certain trait results in the trait increasing in frequency in the next generation

Fitness by natural selection

differential survival and reproduction of individuals with certain traits in the given environment

Fitness

Measures of ability of an individual to survive and reproduce in a particular environment, leaves its genes in the enxt generation

Adaptations

Traits that increase fitness; new genes to survive new environment

Positive Selection

Natural selection for favorable alleles → increases the frequncies of a favorable allele

Negative Selection

Natural selection against harmful alleles → decrease allele frequency of a harmful allele

Balancing Selection

Selection favoring allelic variation → Multiple alleles are maintained at intermediate levels

Stabilizing selection

Results in selection against extreme phenotypes

Directional Selection

Only selects for or against extreme phenotype; shifts the distribution of a phenotype so the mean value increases or decreases in the population ( Graph shifts left or right )

Disruptive Selection

results in selection against intermediate phenotypes and is thought ot be important for certain speciation processes

Artificial Selection

[ Form of directional selection ], successful genotypes are selected y the breeders, not by competition

Indirect Competition

One sex chooses members of the other sex based on phenotype criteria

Direct Competition

Between individuals of the same sex

Inter selection

Focuses on interactions between male and female ( Indirect Competition )

Intra selection

Males fighting for access to females ( Direct Competition )

Adaptive mechanisms of evoluton

• Driven by environmental pressures

• Favors traits that improves survival and reproduction

• Leads to better fit between organisms and environment

• ex. Direction, disruptive, stabilizing, balancing, and sexual selection

• Natural Selection

Non-Adaptive Mechanisms of Evolution

• Not driven by natural selection or fitness differences

• Occurs regardless of whether traits are beneficial, harmful, or neutral

• Can increase or decrease genetic variation by chance

• ex. genetic drift, genetic flow (migration), mutations

Genetic Drift

[non-adaptive], allele frequencies change due to chance - depends on population size and allele change over generations

Population bottleneck

A population is drastically reduced in size - negative results in environment resulting in love survival rates

Founders effect

occurs randomly, reduces genetic diversity - Occurs when a few individuals become isolated from a larger population

Migration

Connects population by allowing gene flow between them, resulting in allele frequencies to change

Gene flow

population becomes more genetically similar over time - matting with individuals of another population and becoming all one

What must occure for a popualtion to be consisdered seperate species

Population results be reproductively isolated

Pre-Zygotic

Reproductive isolation happens before fertilization

Post-Zygotic

Reproductive isolation happens after fertilization

Pre-Zygotic Mechanisms

1. Geographical / Ecological

2. Temporal

3. Behavioral

4. Gametic

5. Mechanical

Pre-zygotic Geographical / ecological

Individuals are separated in space or habitat

Pre-zygotic Temporal

Plant flowers at different times, and animals are active at different times

Pre-zygotic Behavioral

Individuals only male with other individuals based on specific behavior

Pre-zygotic Gametic

Incompatibilities exist between gametes

Pre-zygotic Mechanical

Species reproductive organs are incompatible

Post-zygotic hybrid inviability

After fertilization, a zygote fails to develop

Post-zygotic hybrid sterile

Offspring are produced but are sterile

Speciation

the process of one species splitting into and species as a by product of genetic divergence

Allopatric Speciation

Barrier forming between both species

Initial speciation

Can result in evolution during each population diverging until they are reproductively isolated

Dispersal (Allopatric)

Individuals colonize a new area

Vicariance (allopatric)

Where a geographic barrier arises, a population splits into two separate population - overtime, the time population will become genetically distinct from one another until speciation occurs

Disruptive Speciaiton

Can drive reproductive isolation in the absence of physical separation

Sympatric Speciation

Can be driven by hybridization - in hybridization, the number of chromosomes can be different from either parental species → as this occurs, hybrids are reproductively isolated from parents because of gamete incompatibilities

Sister taxa

Groups that an immediate common ancestors not shared by any other group

Phylogentic Trees

Shows pattern of descent, does not generally show how old lineage are or how much they have changed

Example of Stabilizing Selection

In a fish species, the eggs tend to be fertilized more often by the mid-sized males and less often by the largest and smallest males - results in selection against extreme phenotype

Example of directional selection

Environmental conditions - food source characteristics - causes selection towards one extreme of a traits range of variation

Polyphyletic

Consists of taxa that share a trait that is not present in their most recent common ancestor

Paraphyletic

Incudes a common ancestor and some but not all of the descendants

Monophyletic

Includes a common ancestor and all of its descendants

Recombinations and Mutations

Produce new alleles in a population

Genetic Variation

Critical for evolution because it is the source material for natural selection