Other Mechanisms of Change

THEORY OF EVOLUTION

WHAT ARE WE LEARNING TODAY?Benchmarks SC.912.L.15.13 – Describe the

conditions required for natural selection, including: overproduction of offspring, inherited variation, and the struggle to survive, which result in differential reproductive success.

SC.912.L.15.15 – Describe how mutation and genetic recombination increase genetic variation.

SC.912.L.15.14 – Discuss mechanisms of evolutionary change other than natural selection, such as genetic drift and gene flow.

Learning Objectives I will explain and describe

how mutation and genetic recombination increase genetic variation.

I will explain and describe the scientific mechanisms, such as genetic drift, gene flow, and nonrandom mating, resulting in evolutionary change.

Evolution is the change in a population’s genetic material over generations.

Four other mechanisms of evolutionary change exist besides natural selection. Mutations Gene flow Genetic drift Nonrandom mating

WHAT ARE OTHER MECHANISMS OF EVOLUTION?

A mutation is a change in the genetic material of a cell.

Mutations affect evolution by producing totally new alleles.

Germ mutations occur in the reproductive cells, or gametes, of an individual. These mutations can be passed

on to the offspring. They can affect the survival of an

individual organism or a genetic line of organisms.

WHAT ARE MUTATIONS?

Mutations can be:1. Neutral- No affect• No pattern of increase

or decrease in allele frequency

2. Harmful• Usually naturally

selected against and rid of in short time

3. Beneficial• usually increase over

time

WHAT ARE MUTATIONS?

Gene flow is the process of genes moving from one population to another.

Gene flow can occur through Immigration ( the

movement of individuals into a population)

Emigration (the movement of individuals out of a population)

WHAT IS GENE FLOW?

Genetic drift is the process by which alleles frequencies in a population change as a result of random events, or chance.

It can result in substantial changes within a population.

Only significant in small and medium-sized populations.

WHAT IS GENETIC DRIFT?

Nonrandom mating occurs whenever individuals may choose partners.

Influenced by geographic proximity and assortative mating

Sexual selection occurs when certain traits increase an individual’s success at mating.

WHAT IS NONRANDOM MATING?

REVIEWWe have discussed how evolution by natural selection works

• NATURAL SELECTION requires:

1. Overproduction of offspring

2. Inherited Variation

3. Struggle to survive

4. Differential Reproduction

• We have discussed several ways natural selection can act on populations• *Genetic drift

• Gene flow

• Mutations

• Non-random mating

You should be able to explain/describe each of these concepts by now

LETS GO OVER GENETIC DRIFT AGAIN

• Genetic Drift is a RANDOM change in allele frequencies in a population due to a completely random event

• 2 types of Genetic Drift Situations:

1. Bottleneck effect

2. Founder’s effect

GENETIC DRIFT: BOTTLENECK EFFECT

Sometimes a random disaster may kill many individuals in a population.

Those alleles left may not be the same representation as the original population

GENETIC DRIFT: FOUNDER’S EFFECT

Migration of a small subgroup from a main population leads to a difference in allele frequencies from the original population’s

The founding population will reproduce and pass on the alleles of the founders

Punctuated Equilibrium• Change occurs in spurts

• Period of little change, followed by period of huge change

• Change is noticeable and abrupt

Gradualism• Small changes occurring little by

little

• Usually hard to notice over short period of time

• Change is slow, constant, and consistent

RATES OF EVOLUTION: PUNCTUATED EQUILIBRIUM VS GRADUALISM

GradualismPunctuated Equilibrium

3 TYPES OF NATURAL SELECTION

1. Directional Selection• Better “fitness” toward 1 direction

• Example: bigger the beak, the better fit

2. Stabilizing Selection• The intermediate trait is best fit

• Example: the grey species is better fit than the white or black

3. Disruptive Selection• the extreme, or outer end traits are better fit than the

intermediate trait

• Example: the white and black species is better fit than the grey species

3 TYPES OF SELECTION

MICROEVOLUTION VS MACROEVOLUTION

• Microevolution is evolution based on the genetic level

• Genetic drift

• Mutation

• Nonrandom mating

• Gene flow

• Macroevolution is evolution based on more visually observable changes in species

• Extinction

• Speciation

• Adaptive radiation

• Convergent Evolution

• Co-evolution

EXTINCTION AND SPECIATION

• Extinction is when a species disappears forever from the earth as a result to its population being completely diminished

• Speciation is the formation of new species from already existing species

• But how do new species form?

• Geographic isolation

• Temporal isolation

• Behavioral isolation

Reproductive isolation New Species

REPRODUCTIVE BARRIERS

PRE- Reproductive Barriers

• Habitat Isolation

• Geographic isolation

• Temporal isolation

• Mechanical isolation

• Behavioral isolation

• Gametic (reproductive) islation

POST- Reproductive Barriers

• Hybrid Sterility

• Reduced Hybrid Viability

ADAPTIVE RADIATION

A single species evolves over a relatively short period of time into several forms that live in different ways

Galapagos finches evolved different beaks and behaviors that allow them to eat different kinds of food

CONVERGENT EVOLUTION

When distantly, unrelated species LOOK similar because they have evolved in similar environments

CO-EVOLUTION

Sometimes 2 different species live and interact so closely together, they evolve together

The evolution of one species drives the evolution of the other

EXAMPLE:

• Flowers and pollinators