Bio 102: Theme 3- Evolution: Change Over Time

Evolution

change over time in frequencies in a population

Population

group of individuals of the same species that interbreed

What does evolution do?

changes populations

What is frequency equivalent to?

Proportion

What is the equation for solving population numbers?

part / whole = count of target / count of all

Gene Pool

set of alleles in a population 

High Genetic Diversity

population with large gene pool (many alleles)

Heritable

passed down from parents has a genetic basis

Populations evolve through:

• natural selection

• genetic drift

• gene flow

• mutation

Natural selection

individuals with better phenotypes tend to produce more offspring because of the phenotypes

Genetic Drift

Fitness differences in individuals because some individuals are luckier than others

Gene Flow

alleles move between populations that can cause change in a population

Mutation

new alleles can arise from mistakes in DNA replication

Fitness

ability to survive and produce surviving offspring

• survival of the alleles/genetic combination

What does SURVIVAL of the FITTEST mean?

Survival= specific alleles persist

Fittest= tend to produce more offspring

Normal Distribution

curve that’s symmetrical around the mean

• individual with mean value are most common

Stabilizing selection

narrowing

Directional selection

population phenotype becomes more like an extreme

• shifts right or left 

Disruptive selection

disrupts how selection works 

Adaptation

natural selection makes populations better adapted

Sexual Dimorphism

males and females have different phenotypes

Sexual selection

individuals with certain inherited traits produce more surviving offspring

• there is strong selection pressure for traits that produce the most surviving offspring

Intersexual selection

opposite sex is the “selector”

Intrasexual selection

selection happens between same sex

Ex: moose (male to male)

How can a trait evolve by sexual selection?

if it increases the individual’s fitness

Artificial Selection

breeders select the individuals with desirable traits and use them to create the next generation

Meiosis

creates diversity without adding new alleles

How does meiosis create diversity?

1. Crossing over

2. Independent assortment

3. combinations are new, but the parts aren’t new

How is mutation important?

Adds new alleles to the deck

How much of our genome is uniquely our own?

approximately 30%

What are most mutations?

Mostly neutral with no effect

What happens when a mutation does have an effect? 

They are mostly harmful, but sometimes beneficial 

What does random mean?

All possible are equally likely

• an alleles is jut as likely to become more common than less common

Bottleneck event

random population change due to a disaster

Founder effect

few individuals “found” (create) a new population, and new population’s genetic make-up is a random subset of initial population

Which patterns of evolution cause fitness differences?

1. (Natural) selection

2. Genetic Drift

Gene Flow

new alleles come along with migrating individuals 

What patterns of evolution cause new alleles

1. Mutation

2. Gene Flow

Dispersal

movement from one place to another

• sometimes over very, very long distances

Does evolution have a goal?

No, it has no goal. It is random.

Which patterns of evolution increase genetic diversity?

1. Gene Flow

2. Mutation

Which patterns of evolution decrease genetic diversity?

1. Natural Selection

2. Genetic Drift