Bio Honors Unit 11

Micro evolution

Micro evolution

Small adaptive changes within a species' gene pool when relative frequencies of alleles in a population change over a number of generations; evolution at its smallest scale.

Population

Localized group of individuals that can potentially interbreed and produce fertile/sexually viable offspring.

Gene pool

Total amount of copies of every type of allele at very locus in all members of a different population

Genetic Equilibrium

A condition in a population where the gene pool and allelic frequencies remain unchanged after several generations; population is not evolving

Hardy-Weinberg Theorem

A. A population's gene pool remains constant from generation to generation

B. The frequency of alleles remains constant

C. The frequency of genotypes remains constant

5 Conditions for Hardy-Weinberg Equilibrium

1. No mutations

2. Random mating

3. No natural selection

4. Extremely large population size

5. No gene flow

Importance of Hardy-Weinberg Theorem

It is used to predict the allele frequency and genetic equilibrium overtime in a population; constant gene pool.

Why are genetically lethal diseases never completely eliminated from a population?

Heterozygotes are healthy and live to reproduce. The result is the lethal or harmful allele gets concealed in the population and passed on to offspring.

Hardy-Weinberg Equation

p^2 + 2pq + q^2 = 1 & p+q = 1

What does p equal in the Hardy Weinberg equation?

frequency of homozygous dominant allele

What does q stand for in the Hardy-Weinberg equation?

frequency of homozygous recessive allele

What does pq stand for in the Hardy-Weinberg equation?

Frequency of heterozygous allele

What causes populations to evolve?

Factors disrupting Hardy-Weinberg equilibrium

Major Factors Driving Microevolution

Mutations, Gene Flow, Genetic Drift, Non-random mating, and Natural Selection

Mutations

a random error in gene replication that leads to a change, the only way to generate new alleles or new genes or new species. *Not a major way microevolution occurs

Problems with Mutations

The mutation is not passed on to offspring unless in a gamete cell. Most single nucleotide DNA mutations have no effect and are silent mutations. Mutations that are not silent are typically harmful to the organism.

When are Mutations Beneficial?

When an environment change occurs making that mutation important for the organism's survival.

Gene Flow

The loss or gain of alleles as individuals migrate to new populations resulting in the reduction of genetic differences between populations.

Genetic Drift

A change in a populations gene pool due to chance and requires a small population size

Two types of genetic drift

bottleneck effect and founder effect

Bottleneck Effect

A change in allele frequency following a dramatic reduction in the size of a population. Causes alleles to be eliminated and some to increase in frequency. Completely RANDOM and not based on the "fittest".

Founder Effect

occurs when a few individuals become isolated from a larger population to stat a new population. Results in less genetic variation the smaller the migrating population. Usually results in increase for frequency in diseases or mutations (E.g. The Amish).

Natural Selection

A process in which individuals that have certain inherited traits tend to survive and reproduce at higher rates than other individuals because of those traits.

Natural Selection & Microevolution

The ONLY FACTOR driving microevolution that ALWAYS has a POSITIVE EFFECT and is NEVER RANDOM. Acts on the organism's phenotype NOT on the genotype.

How does natural selection cause a positive change in microevolution?

differential reproductive success

Microevolution

evolutionary change within a species or small group of organisms, especially over a short period. (E.g. One organism into another type of organism, SPECIATION)

Speciation

Original and development of new species by evolution

What is a species?

We don't entirely know—but the working definition is called the biological species concept.

Biological Species Concept

a population or group of populations whose members can interbreed and produce fertile offspring

Requirement for Biological Species Concept

Members of the population are not reproductively isolated but able to maintain genetic variation. The limitation is though that this theory cannot account for fossils or asexual organisms.

Other ways to define species

Morphological species concept, paleontological species concept, ecological species concept, genealogical species concept.

Morphological Species Concept

Species are defined based on body shape, size, and structural features

Paleontological Species Concept

Species are defined based on the the morphology that is observed only in the fossil record

Ecological Species Concept

Species are defined based on the particular microenvironment where the organism lives

Genealogical Species Concept

Species are defined based on the genetic history of the organism and their location on tree of life (molecular evidence)

How are species formed from existing species?

Microevolution occurring in isolation

Types of Reproductive Isolation

prezygotic and postzygotic

Pre-Zygotic Barriers

Barriers that prevent the formation of a fertilized egg

Post-Zygotic Barriers

Barriers that prevent an organism from developing into a fertile adult

Five types of Pre-Zygotic Barriers

habitat, temporal, behavioral, mechanical, gametic

Mechanical Isolation

A difference in the morphology of the two species prevents successful mating. (E.g. snail mating—shell swirls)

Gametic Isolation

The sperm cannot fertilize the egg

Behavioral Isolation

Species use a courtship ritual to attract mates resulting in males and females freedom other species not being attracted to each other. (E.g. Bird Dances)

Habitat Isolation

The two species DONT come into contact with each other (E.g, Garter Snakes—one is in water and the other on land).

Temporal Isolation

occurs when two species breed at different times of day, month, or year. (E.g. Eastern and Western Spotted Skunk)

Three Types of Post-Zygotic Barriers

reduced hybrid viability, reduced hybrid fertility, hybrid breakdown

reduced hybrid viability

The hybrid offspring do not fully develop and die before reaching sexual maturity

Reduced Hybrid Fertility

The hybrid offspring are sterile and cannot produce sperm and egg (E.g. Mule, Liger, Tigon)

Hybrid Breakdown

The first generation of hybrids are fertile, but the second generation are sterile.

Speciation Process

Requires reproductive isolation and geographic barriers to block gene flow. Different natural selection factors act on changes causing the subpopulations to diverge. When they can no longer interbreed and produce viable offspring they are a new species.

Speciation Due to Behavioral Isolation

Reproductive barrier based on preference and traction and mating rituals (E.g. Cichlid Fishes having a color preference when choosing mate)

Adaptive Radiation

The evolution and diversification of a common ancestor into many new species. The action of natural selection is the mechanism. Occurs often as a result of the founder effect and extinctions.

Cambrian Explosion

A burst of evolutionary origins when most of the major body plans of animals appeared in a relatively brief time in geologic history; recorded in the fossil record about 545 to 525 million years ago. Huge increase in diversity of invertebrates and the appearance of the first vertebrate ancestor. This appears to contradict Darwin's theory of gradual descent with modification.

Hypotheses to Explain Cambrian Explosion

Predator-Prey relationships, Increase In Atmosphere Oxygen, HOX Genes. (Most likely a combination of all three)

Predator-Prey Relationships

An increase in predation resulted in an increase in natural selection; species that couldn't adapt declined and other species increased

Increase in Atmosphere Oxygen

Just prior to the Cambrian period, the first photosynthetic organisms emerged allowing for the support of larger, complex organisms

HOX Genes

Genes that are involved in the Embryological development of an organism/ As life increases in complexity, the number of HOXgenes the organism has increases due to gene duplication

Punctuated Equilibrium

Says that a new species changes the most from its parent species early on during new species formation and then changes little for the rest of its existence

Implications of Punctuated Equilibrium

There would be very few transitional fossils that exhibit slight changes in structure and form; transitional fossils would appear sporadically, and a long period of stability in the organism would be "punctuated" by the appearance of a significantly different form.

Evidence for Punctuated Equilibrium

1. Cichlids in Lake Victoria show that once speciation starts that it occurs rapidly

2. Cichlids in Uganda showed speciation in as little as 5,000 years

Important Note on Punctuated Equilibrium

A. It appears that the major factor resulting in punctuated equilibrium is the length of time between speciation events

B. Most speciation times range from 500,000 years to 65 million years

Other Explanations on The Apparent Inconsistency of the Fossil Record

The fossil record may be deceiving (can only detect large periods of time), the appearance of stasis may be deceiving (you can't observe biochemical changes in fossils or changes in behavior, etc.), and molecular evidence suggests that organisms began diverging approximately 700 million to 1 billion years ago prior to the Cambrian.