Bio Quiz 5/4

natural/artificial selection, evolution, speciation

Evolution

The process of change over time

* Change in the __frequency of a gene or allele__ in a population’s gene pool over time

Darwin’s Theory of Natural Selection Steps

1. Overproduction
2. Variation
3. Competition
4. Selection

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Overproduction

Each species produces more offspring then can survive

Variation

Each individual has a unique combination of inherited traits

Adaptation

an inherited trait that increases an organisms chances of survival

Why is Variation Important?

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* More variation __within__ a species = increased survival
* Ex: if everyone is the same, they are all vulnerable to the same environmental changes or diseases. 

Competition

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* individuals compete for limited resources
* Food, water, mates
* Natural selection occurs through “Survival of the Fittest


* Not all individuals survive to adulthood.

Fitness

the ability to reproduce

Selection

* The individuals with the best traits/adaptations will survive and have the opportunity to pass its traits to offsprin__g__. 
* Individuals with traits that are not well suited to their environment either die or leave few offspring


* Evolution occurs when __good traits build up in a population__ over many generations and __bad traits are eliminated by the death of individuals.__ 

Natural Selection acts on

phenotype frequencies (changes the frequency of the allele in the population)

Non-random mating/Sexual selection

organisms chose a mate based on desired traits

Immigration or Emmigration

individuals enter the population and produce new genes

Mutations

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* produce new alleles that result in a new phenotype. May provide an advantage. 

Genetic Drit

changes due to random events

Population

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a group of individuals of the same specifies that mate and produce offspring

Gene Pools

all genes and the alleles for those genes present in a populations

Allele Frequency

the number of times an allele occurs in a gene compared to the total number of alleles in that pool for the same gene

Genetic Bottleneck

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* A change in allele frequency following a dramatic reduction in the size of a population
* Could result from disease, rapid climate, or environmental change.
* Can reduce a population’s genetic diversity. 

Founder Effect

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* When allele frequencies change as a result of the migration of a small subgroup of a population. 
* Creates a new gene pool that could be different from the parent population.

Descent with Modification

Each living species has descended, with changes, from other species over time

Common descent

all living organisms are related to each other. 

Evidence of Evolution

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* Fossil records
* Homologous body structure 
* Vestigial organs
* Embryology
* Biochemical evidence
* Direct Observation

Fossils

a record of the history of life on Earth

Homologous Body Structures

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* similar anatomy structures in different types of animals because of a common ancestor 
* Differences:
* Function

Vestigial Organs

“leftover” traces of evolution that serve no purpose 

* ex: wings on flightless burds, pelvin bone of a snake

Embryolgy

 embryos of all vertebrates are very similar early on

Biochemistry

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* When comparing the DNA of one species to another, more similarities are found in species that are more closely related
* Ex: Humans and chimpanzees share more than 98% of identical DNA sequences

Direct Observation

* Direct observation: species change


1. Bacteria become resistant to antibiotics
2. Wolves were bred over many generations to become dogs (artificial selection) 

Species

A population whose members can interbreed & produce viable, fertile offspring 

Distinct Species

songs & behaviors are different enough to prevent interbreeding 

How and why do new species originate?

New species are formed by a series of evolutionary processes which cause reproductive isolation 

Reproductive Isolating Mechanisms

* Prezygotic Barriers: before reproduction
* Postzygotic Barriers: after reproduction

Prezygotic Barriers

An obstacle to meeting or to fertilization if mating occurs 

* Geographic isolation  
* Ecological isolation 
* Temporal isolation 
* Behavioral isolation 
* Mechanical isolation  
* Gametic isolation 

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Geographic Isolation

New species occur in different areas

Ecological Isolation

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Species occur in the same region but occupy different habitats so they __rarely__ encounter each other 

Temporal Isolation

Species breed during different times of day, different seasons, or different years and cannot mix gametes 

Behavioral Isolation

Unique behavioral patterns & rituals isolate species 

* Identifies members of species 
* Attract mates of the same species (courtship rituals, mating calls)

Mechanical Isolation

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Morphological differences can prevent successful mating

Gametic Isolation

* The sperm of one species may not be able to fertilize eggs of other species 


* Biochemical barrier: sperm cannot penetrate egg 
* Chemical Incompatibility: sperm cannot survive in female reproductive tract  

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Postzygotic Barriers

* Prevent __hybrid offspring__ from developing into a viable, fertile adult  
* Reduced hybrid viability 

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* Genes of different parent species may interact & impair the hybrid's development 

Reduced Hybrid Fertility

* Even if hybrids are vigorous they may be sterile 


* Chromosomes of parents may differ in number or structure & meiosis\\hybrids may __fail to produce normal gametes__  

Hybrid Breakdown

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Hybrids may be fertile & viable in the first generation, but when they mate offspring are feeble or sterile  

Allopatric Speciation

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* A physical barrier arises and prevents gene flow between populations. 
* Reproductive isolating mechanisms evolve in the genetically diverging populations
* Speciation occurs when the members of the divergent populations can no longer interbreed

Sympatric Speciation

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* New species form within the same home range of an existing species __(no physical barrier)__
* May be:
* Temporal
* Mechanical
* Behavioral

Parapatric Speciation

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* Daughter species form a small proportion of individuals along a common border between 2 populations
* The hybrid zone is formed