BIOL 103 W2: The Nature of Species and Populations

Character

Feature of an organism (e.g. rabbits have hair)

Trait

Specific type of feature (e.g. rabbits can have long hair or short hair)

Allele frequency

How often an allele occurs in a population

Gene

Part of DNA that codes of a specific trait

Locus

Location of a gene on a chromosome

Point mutation

Mutation confined to a single nitrogenous base

Mutation

Unintended alteration to DNA

Meiosis

Production of gametes through cell division

Crossover

Process where homologous chromosomes exchange gene segments during prophase of meiosis in order to increase genetic diversity

Gene duplication

A mutation where a specific gene is produced twice resulting in an extra identical copy of the same segment

INDEL

A genetic mutation that combines insertion of genetic material with deletion of genetic material

Heterozygosity

Having one recessive and one dominant allele

Homozygosity

Having 2 of the same allele types (recessive or dominant)

Species

Group of organisms that can successfully reproduce through interbreeding in nature

Population

Group of species that live in the same geographic area and reproduce within the group

Gene pool

All the different alleles in a population

Sympatric

Population shares environment but don’t interbreed

Allopatric

Population is geographically isolated therefore can’t interbreed

5 conditions of Hardy-Weinberg equilibrium

No mutations, random mating, no natural selection, large population size, no gene flow

Use of Hardy Weinberg equilibrium

Predicts frequency of genes, can assess if populations are evolving

Gene flow

Migrants into isolated populations alter the gene pool by bringing new alleles into the gene pool or altering allele frequency

Genetic drift

By random chance, only select organisms have offspring, skewing the gene pool towards the random alleles (as in the traits are neither advantageous/disadvantageous) the offspring inherit

Founder effect

Small group of individuals migrate to a new place and the gene pool lacks many of the variations found in the original group

Bottleneck effect

A chance event randomly kills organisms, the new gene pool lacks many of the variations found in the original group

Modes of natural selection

Directional, disruptive, stabilizing

Directional selection

A single extreme phenotype is favored so the population’s allele frequency shifts in that direction

Disruptive selection

Favors extreme phenotypes over average ones so the population’s allele frequency shifts toward two extremes

Stabilizing selection

Favors average phenotypes over extreme ones so the population’s allele frequency shifts toward average

Intersexual selection

Individuals of one sex choose a partner from a variety of different options

Intrasexual selection

Individuals of the same sex compete for reproduction

Neutral variation

Traits with no advantage or disadvantage

Genetic variation

Differences in genes and DNA between individuals

Gene variability

Genetic variation at the whole-gene level

Whole-gene level

A gene as a complete functional unit, including introns and exons

How can gene variability be quanitified

Average percentage of heterozygous loci

Nucleotide variability

Genetic variation at the molecular level of DNA

Sources of genetic variation

Production of new genes/alleles through mutation, gene duplication, or other processes

Point mutation

Change of one base in a gene

Main mechanisms that increase genetic diversity

Crossing over, independent assortment, fertilization

Independent assortment of chromosomes

The random way that chromosomes line up during meiosis with each pair having a 50% chance of facing either direction, completely independent of the orientation of the pairs above or below it

How fertilization increases genetic variation

Every fusion of a sperm and an egg are 100% unique because every egg/sperm is different

Population

Group of individuals of the same species that live in the same area and interbreed to produce fertile offspring

Gene pool

All copies of every allele at every locus in all members of a population

Biological species concept

States a species is a group of individuals that can naturally interbreed and produce viable, fertile offspring

Adaptive radiation

When many different, slightly different species rapidly evolve from one common ancestor

Reproductive isolation

Existence of barriers that impede members of two species from producing viable, fertile offspring

Prezygotic barriers

Block fertilization from occurring

Types of prezygotic barriers

Gametic isolation, mechanical isolation, temporal isolation, habitat isolation, behavioral isolation

Postzygotic barriers

Contribute to reproductive isolation after the hybrid zygote has formed

Habitat isolation

Two species occupy different habitats and therefore have limited encounters

Temporal isolation

Species breed during different times of day, seasons, etc. and cannot mix their gametes

Behavioral isolation

Species have different mating rituals that do not attract each other

Mechanical isolation

Physical differences stop attempted mating from being successful

Gametic isolation

Sperm of one species cannot fertilize the egg of another

Types of postzygotic barriers

Hybrid inviability, hybrid infertility, hybrid breakdown

Hybrid inviability

The hybrid’s development or survival is impeded

Hybrid infertility

The hybrid is not able to produce offspring

Hybrid breakdown

A first generation hybrid may be viable and fertile, but their offspring are inviable or infertile

Limitations of biological species concept

Fossils, asexual reproduction, ethical concerns

Morphological species concept

Distinguishes species through body shape and physical features

Ecological species concept

Defines a species by how it interacts with living and non-living features of its environment, accounts for asexual and sexual reproduction

Allopatric speciation

Gene flow is interrupted when a population becomes geographically separated resulting in speciation

Sympatric species

Speciation that occurs in a population inhabiting the same geographic area when gene flow is reduced

Polyploid speciation

A species can originate from a mutation during meiosis that results in an extra set of chromosomes

Factors causing sympatric speciation

Polyploidy, habitat differentiation, sexual selection

Habitat differentiation

When a subpopulation uses a resource or habitat that the parent population does not, resulting in speciation

Hybrid zone

A region where members of different species with incomplete reproductive barriers meet and mate, producing hybrids

Location of hybrid zones

Typically where the habitats of interbreeding species meet

Reinforcement

Since hybrids are usually less fit than parent species, natural selection strengthens prezygotic barriers to reproduction to reduce unfit hybrid offspring

Fusion

Reproductive barriers may be weak between 2 species allowing so much gene flow that it results in “reverse speciation” where the 2 hybridizing species fuse into a single species

Stability

Hybrids continue to be produced in hybrid zones

Punctuated equilibria

Instances in the fossil record of new species appearing suddenly and continue mostly unchanged through several strata before disappearing