DHS Honors Biology (O'Malley) Unit 7: Evolutions of Populations

Causes of Evolution

Causes of Evolution

• Small Population

• Non-random mating

• Mutation

• Migration

• Natural Selection

Natural Selection

Any situation which more individuals are born than can survive given the environment

Genetic Diversity

Creates heritable variations

Levels of Fitness

Organisms express different _____ as a result of genetic diversity

Survival of The Fittest

The most “fit” organisms will be the most successful at reproducing and passing their genes on

Adaptations are often compromises (True / False)

True

Not all evolution is adaptive (True / False)

True

Selection can only edit variations that exist

True

Mechanisms of Natural Selection

• Stabilizing

• Directional

• Disruptive

Stabilizing Mechanism

Ex. Human birth height & weight

Directional Mechanism

One extreme phenotype is favored. Ex. Sickle cell trait & Malaria

Disruptive Mechanism

Both extreme phenotypes are favored.

Artificial Selection

Selective breeding, intentionally pairing two organisms together so that they breed and the offspring has desirable traits

Population Genetics

• Large Population Size

• Random Mating

• No Mutations

• No Migration

• No Natural Selection

When Does Evolution Occur?

Changes in allele frequencies within a population

Causes of Microevolution

• Genetic Drift & Bottleneck Effect

• Founder Effect

Genetic Drift & Bottleneck Effect

• Genetic Drift: Random changes in allele frequencies due to chance events in small populations. Can lead to loss of genetic variation.

• Bottleneck Effect: A sudden reduction in population size that can cause genetic drift. Can lead to reduced genetic diversity and increased risk of genetic disorders.

Founder Effect

Reduced genetic diversity which results when a population is descended from a small number of colonizing ancestors.

Sexual Selection

Process where opposite sexes (males and females) mate in order to reproduce

Law of Use or Disuse (Lamarck)

Acquired Characteristics, if the environment changes then animals will change their phenotype in order to survive and it will be directly passed on to the offspring.

Charles Lyell

Uniformitarianism

Thomas Malthus

Resouces grow linearly, and populations grow exponentially (ecology population graphs)

Uniformitarianism

• The earth changes slowly over time

• The earth has always changed the same way

Charles Darwin Theory of Evolution by Natural Selection

• Descent with modification

• Natural selection is differential success in reproduction

• Natural selection occurs through interaction with the environment

• Product of natural selection is adaptations in populations

Origin of Life

• Panspermia

• Abiogenesis

Panspermia

“Seeds” of life spread across the universe to suitable planets

Abiogenesis

Life came from non-living substances that organized into the first cell

Spontaneous Generation created life (True / False)

• False

• Francesco Redi

• Louis Pasteur

Francesco Redi

• Redi used jars of meat to disprove spontaneous generation.

• He set up three jars: one open, one covered with gauze, and one sealed shut.

• Maggots only appeared in the open jar, proving that they came from flies, not spontaneously generated from the meat.

Louis Pasteur

• Louis Pasteur's experiment involved disproving spontaneous generation of microorganisms, which was the idea that microbes could arise from non-living matter.

• He used two flasks, one with a straight neck and one with a curved neck, both filled with nutrient broth. The straight-necked flask allowed dust and microbes to enter, while the curved-necked flask prevented them from reaching the broth.

• he broth in the straight-necked flask became cloudy with microbes, while the broth in the curved-necked flask remained clear, demonstrating that microorganisms did not arise spontaneously but came from outside sources.

Earth’s Geological History

1. AGE: 4.6 Billion

2. Moon

3. Zircon Crystal

4. Fossils

5. Rise in Oxygen %

6. First Cell

7. Animals Dinosaurs

Conditions of the Atmosphere

• Watch this video

• The early Earth was formed through violent collisions of rocks, metals, and ice.

• The first atmosphere was created from the release of water vapor and gases, which eventually thickened into a blanket of steam.

• The impact of a Mars-sized object coalesced with Earth and formed the moon.

• The first microbial organisms evolved and contributed to the oxygenation of the atmosphere.

• The rise of oxygen caused a reduction in greenhouse gases and led to mass glaciation on Earth.

RNA World Hypothesis

• The origin of life is still a mystery to science.

• DNA is a great information storage, but cells rely on other molecules to survive.

• RNA can store information and perform functions to keep cells alive.

• Scientists believe self-replicating RNA formed first in a primordial soup of molecules.

• RNA evolved into molecular machines and eventually some critical RNA mutated into DNA.

Miller Urey Experiment

• Created conditions of Oparin’s hypothesis in a lab setting

• Organic compounds including amino acids were formed.

• Simulated early Earth conditions

• Sparked with electricity

• Produced amino acids

• Showed organic molecules can form

• Key to understanding life's origins

Oldest Fossilized Cells

Cyanobacteria (3.6B YR) found in stromatolites

Atmosphere Fosters Life

Oxygen levels rise (2.4B YR)

Six Thresholds of Life

• Photosynthesis

• Eukaryotes

• Multi-cellular organisms

• Development of Brains

• Inhabit Land

• Mammals

Endosymbiosis

• Biological phenomenon where one organism lives inside another, forming a mutually beneficial relationship.

• Mitochondria have origins as proteobacteria

• Chloroplasts have origins as cyanobacteria

• Both were used in a eukaryotic cell for metabolic processes

Mass Extinction

Rapid extinction of 75% or more (90-99 % of all species have gone extinct)

Background Extinction

• Normal Rate: 1 to 5 Species / yr

• Due to anthropogenic causes

• Actual Rate: 1k to 10k

Human Extinction

Humans almost went extinct due to a volcano eruption

Cladogram (Phylogenetic Tree)

Diagram that depicts evolutionary relationships

Evidence for Evolution

• Biogeography

• Fossils

• Embryology

• Genetic Differences

Biogeography

The continental drift and plate tectonics of the past and present influence the distribution and formation of species.

Absolute vs Relative Dating

Relative dating determines the order of past events without giving an exact age, while absolute dating provides a precise age for geological materials (usually of rocks).

Carbon-14 Dating

Measures the decay of radioactive carbon atoms in once-living organisms to determine when they were last alive. Carbon-14 has a half-life of 5,730 years, limiting its use to dating items that lived on Earth within the last 50,000 years.

Cast

Imprint fills in with minerals from sediment and groundwater, it can harden to form a _____.

Actual version of the animal

Mold

An imprint of the cast.

Intact Remain

Physical remains of an organism that are preserved without any significant damage or alteration.

Index Fossil

Used to identify the age of rock layers and are typically abundant, widespread, and existed for a relatively short period of time.

Embryos

Different species classes share similar embryo features (gills, yolk sacs, notochords)

Genetic Differences

% of differences between genomes of species indicate evolutionary similarities

Molecular Clock

Research tool that uses mutation rate to approximate time which divergence (change) occurred

Homologous Structures

Related Species & Different Purpose (Form)

Ex. Limbs

Divergent Evolution

Selective pressures that favor different purposes, leads to homologous structures

Adaptive Radiation

The process by which a single species or a small group of species evolves over a relatively short time into several different forms that live in different ways

Ex. Galapagos Finches

Analogous Structures

Unrelated Species & Same Purpose (Form)

Convergent Evolution

Selective pressures that favor similar purposes, leads to analogous structures

Vestigial Structures

Morphological (relating) structures that have lost their function, but not their forms through evolution (Ex. ear muscles, wisdom teeth, body hair, male nipples)

Coevolution

• Two species evolve in response to each other’s changes over time

• Flowers & Pollinators

• Plants and Insects

• Parasites & Hosts

Reproductive Isolation & Speciation

Prezygotic Isolation vs. Postzygotic Isolation

Prezygotic Isolation

• (Geographic Barrier)

• Habitat Isolation

• Behavioral Isolation

• Temporal Isolation

• Mechanical Isolation

• Gametic Isolation

Postzygotic Isolation

• (Behavioral Barrier)

• Reduced Hybrid Viability

• Reduced Hybrid Fertility

Temporal Isolation

Timing of reproduction differs among species

Mechanical Isolation

Species genitalia are incompatible

Gametic Isolation

Gametes are incompatible (sperm and egg)

Reduced Hybrid Viability

Embryo dies, never develops into a fetus

Reduced Hybrid Fertility

Uneven number of chromosomes, offspring cannot reproduce

Ex.

• Horse + Donkey = mule

  • Mule + Mule = 💀

• Lion + Tiger = Ligers or Tigons

  • Liger + Liger = 💀

Forms of Speciation

Allopatric vs. Sympatric

Allopatric

Geographic barrier and founder effect (Ex. Adaptive Radiation)

Sympatric

Competition pressures within a population (Ex. African Cichlids and the second set of jaws (fish))

Rates of Speciation

Gradualism vs. Punctuated Equilibrium

Gradualism

Slow gradual accumulation of changes over time

Clear Easy Fossil Record, Common Ancestor

Punctuated Equilibrium

Short, Rapid change followed by periods without change

Does not have fossil evidence

Species

A group of living organisms that share common characteristics and can interbreed to produce fertile offspring.