Biology - Unit 3

Evolution

change in genetic traits over successive generations, include microevolution (Small scale) and macroevolution (Large-scale evolutionary changes, including the formation of new species)

Adaptation

a structure, behavior, or physiological process that helps an organism survive and reproduce in a particular environment

Variation

a visible or invisible difference among some members of a population.

How do adaptations develop? 

Adaptations are the result of a gradual change in the genetic traits. Traits(also called variations) that are beneficial may be passed on to the next generation.

Examples of types of adaptations

 

Structural adaptation	Fish gills
Behavioral adaptation	Hibernation Mating & courtship rituals Mudfish Dance
Physiological adaptation	Release of a toxin to protect themselves from predators

Causes of variations within a species

 

Event	How does it increase genetic variation?
Crossing over	The exchange of genetic material during meiosis increases genetic variation because it makes the offspring more different than their parents.
Sexual reproduction	When sperm and egg combine the offspring are genetically different than the parents
Mutations	When genes change in DNA the results can be harmful, neutral or beneficial.  If they are beneficial they may help an organism survive in its environment, which means that the organism is more likely to survive and reproduce.

Selective advantage

Heritable characteristic that improves an organism’s chance of survival in its environment such as Sickle Cell Anemia

Natural selection

 

	Artificial selection (selective breeding)	Natural selection
Definition	Humans select for desirable traits rather than leaving the species to evolve.	A process that favors heritable traits that increase the survival chances of an organism
Example	Dog breeding Mendel’s peas	industrial melanism in peppered moths  antibiotic resistance in bacteria

What is the impact of artificial selection on genetic diversity?

It creates less genetic diversity!

Selective pressure

external factors which affect an organism’s ability to survive in a given environment. Selective pressures can be negative (decreases the occurrence of a trait) or positive (increases the proportion of a trait) and may result in extirpation or extinction.

Examples of selective pressures

 

Resource availability	Not enough food, mate or habitat
Environmental conditions	Too cold or hot
Biological factors	Predators and pathogens (diseases)

Darwin vs Lamarck

Jean Baptiste Lamarck - Law of acquired characteristics - characteristics, such as large muscles, that were acquired during an organism’s lifetime could be passed on to its offspring. Law of use and disuse - use the trait or lose it.

Charles Darwin - Theory of Natural Selection. Father of Evolution.

Theory of Natural Selection

1. Variation - Among the offspring, there are different traits. Eg: goldfish have golden, orange and/or brownish scales

2. Competition - Survival of the fittest.  More offspring are born than ever survive to become adults (an idea by Thomas Malthus). Eg: Female fish can lay thousands of eggs, but only a few survive to become adults.

3. Adaptations -the best adaptations, determined by the environment, are passed on.

4. Selection - Survivors pass on their traits to the next generation.

   Over millions of years, such gradual changes lead to changes in the whole population and hence to the origin of an entirely new species.

   
   

Fossil record

remains or traces of past life preserved in sedimentary rock, which reveal the history of life on Earth

Fossil Records examples

 

Index fossils	Fossil species that are known to be common during a certain time. Eg trilobites
Radiometric dating	This method uses measurements of certain radioactive isotopes to calculate the absolute age in years of rocks and minerals. Eg: It takes 5730 years for Carbon-14 to decay into Nitrogen-14
Transitional fossils	Fossils that show intermediary links between groups of organisms. Eg: scientists have found fossilized whales that lived 36 to 55 million years ago. These fossils link present-day whales to terrestrial ancestors.

Biogeography

 the study of the past and present geographical distribution of species. Darwin and Wallace hypothesized that species evolve in one location and then spread out to other regions.

Eg: Lemurs are primates found only on the African island of Madagascar. Because of its geographic isolation, Madagascar is home to many animals found nowhere else on Earth.

Comparative anatomy

study of the body structures of different species of animals in order to understand evolution.

Comparative anatomy examples

 

Homologous structures	Physical features with the same evolutionary origin, but that may have different functions.  Eg: limbs of vertebrates
Analogous structures	Physical features that evolved separately but perform similar functions in different types of organisms.  Eg: bird wing vs. butterfly wing
Convergent evolution	tendency among species that are not closely related to develop similar body plans when living under the same conditions.  Eg: sharks and dolphins
Vestigial structures	anatomical features that no longer retain their function.  Eg: tailbone in humans

Comparative embryology

 the comparison of embryo development across species.

Molecular biology and genetics

Comparison of DNA and proteins from different species to support the idea of common ancestry and evolution through natural selection. Eg: humans and chimpanzees

What are two types of DNA analysis that scientists can use to determine the evolutionary relationship between two organisms?

1. DNA sequencing - to determine the genes that are similar

2. PCR - amplify DNA to make more to study it

Geologic time scale 

A system of chronological dating that classifies geological strata (stratigraphy) in time. It is used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events in geologic history.

Why are the Ediacaran and Cambrian periods so significant to animal evolution? 

 

Time period	Description	Significance
Ediacaran Period (635 to 542 mya)	Many of the animal groups living today first appeared in the fossil record. Not many fossils from this period because animals were soft-bodied.  Mistaken Point Ecological Reserve -  earliest fossils ever recorded.	First evidence of multicellular complex life forms
Cambrian explosion (530 mya)	The basic body plans (i.e. skeletons, shells, brittle coatings) of the major animal phyla are established ~ 10 million years	All the major animal phyla that exist today evolve during this time.

How can species become reproductively isolated?

 

Geographic isolation	features such as mountain that physically separates populations and so prevents them from interbreeding
Biological isolation	features of different populations that keep them reproductively isolated, even when they exist in the same geographic area

Prezygotic Barriers

prevent organisms from different species mating or prevent successful fertilization of the eggs of one species by the sperm of the other.

Examples of Prezygotic Barriers

 

Behavioral isolation	species-specific signals or behaviors prevent interbreeding with closely related species. Eg: bird calls
Ecological/habitat isolation	different species live in the same general area, but they use different habitats so they encounter each other rarely, if at all. Eg: water snake and land snake
Temporal isolation	two species may occupy the same habitat but mate or flower at different times of the day, in different seasons, or years. Eg: wood frog and leopard frog
Mechanical isolation	species that are closely related have incompatible reproductive structures.
Gametic isolation	If egg and sperm from different species do meet the gametes will rarely fuse to form a zygote. DNA does not match.

What is a Hybrid?

An offspring from two different species. The hybrid offspring are infertile or not viable

Ex: horses and donkeys can mate and produce offspring called a mule which is infertile. 

Postzygotic barriers 

Prevent hybrid zygotes from developing into viable, fertile adults.

Examples of Postzygotic barriers 

 

Hybrid inviability	a genetic incompatibility of interbred species that stops development of the hybrid zygote during its development. Eg: hybrid embryos between sheep and goats leads to a miscarriage or stillborn birth
Hybrid sterility	Two species can mate, but the offspring is sterile (cannot reproduce). Eg:  horse and donkey can make a mule, but the mule is sterile
Hybrid breakdown	The first-generation hybrids of crossed species are viable and fertile. However, when these first-generation hybrids mate they produce offspring that are sterile or weak

How do new species form? 

 

Speciation	The evolutionary process by which populations evolve to become distinct species.
Transformation	One species changes into another species
Divergence (adaptive radiation)	Diversification of a common ancestral species into a variety of differently adapted species

Coevolution

a change in the genetic composition of one species (or group) in response to a genetic change in another.  Eg: flowers and bees

How can rising temperatures on Earth effect how polar bears evolve?

1^st – variation within the species (ex: small, medium & large bears)

2^nd – those with the “best” adaptations were more fit (ex: small, thin bears can swim farther to hunt food)

3^rd – competition - they survived in the environment 

4^th - selection - passed on their traits to offspring

What is the difference between gradualism and punctuated evolution models? 

 

Gradualism evolution model	Punctuated evolution model
model that describes evolution as slow, steady, and linear, with many small changes producing large changes	model that describes evolution as consisting of long periods of stasis, interrupted by periods of rapid change

Population genetics

the study of genetic variation in populations

gene pool

sum of all alleles for all the genes in a population

genotype frequency

proportion of a population with a particular genotype, usually expressed as a decimal

phenotype frequency

proportion of a population with a particular phenotype, expressed as a decimal or percent

allele frequency

rate of occurrence of a particular allele in a population with respect to a particular gene.

Five conditions upon which the Hardy-Weinberg principle is based:

1. The population is large enough that chance events will not alter allele frequencies. 

2. Mates are chosen on a random basis. 

3. There are no net mutations. 

4. There is no migration. 

5. There is no natural selection against any of the phenotypes

What is the difference between founder effect and bottleneck effect?

 

Founder effect	Bottleneck effect
gene pool change that occurs when a few individuals start a new, isolated population	gene pool change that results from a rapid decrease in population size

Causes of Gene Pool Change

 

Small population	net movement of alleles from one population to another due to the migration of individuals
Non-random mating  (sexual selection, inbreeding)	mating among individuals that prevents those with particular phenotypes from breeding, as in mate selection or inbreeding
Mutations	Changes to DNA
Gene flow  (Genetic drift)	change in allele frequencies in a small breeding population due to chance events
Natural selection	The environment selects the best traits. This is the only process that leads directly to evolutionary adaptation.

What is the difference between stabilizing, directional, and disruptive selection?

  

Stabilizing selection	a form of natural selection that favors an intermediate phenotype and acts against extreme versions of the phenotype
Directional selection	a form of natural selection that favors the phenotype at one extreme over the other
disruptive selection	a form of natural selection that favors the extremes of a range of phenotypes over intermediate phenotypes, and may eliminate intermediate phenotypes from the population