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Evolution natural selection
Flashcards for BIO 1 class
List the properties of life
Cellular organization is composed of...
One or more cells
What is a cell formed out of?
Large molecules that contain carbon as a major component
What are the 2 cell types?
Prokaryotic and eukaryotic
When a cell obtains and uses energy
What are examples of work a cell does?
Moving of cell structures
Growing of cells
Production of new cells
Maintain stable internal conditions within and among cells
Produce offspring similar to parents, due to passing of genes from parent to offspring
Increase in size due to increase in number of cells and increase in size of each cell after it is formed
Posses genetic information in the form of DNA molecules
What is the theory of evolution?
Species arise from a series of ancestors, lead back to a common one
Characteristics of new species differ from its ancestors and other descendants
What is natural selection?
Process where individuals that have certain heritable characteristics survive and reproduce at higher rates
Can increase adaptation of the members of a population to their environment
What were Darwin's observations?
Individuals in a population differ in their traits, which are heritable
Members of a population produce more offspring than can survive in environment
Competition for limited resources occurs among members of population
Individuals w/traits best suited to local environment have higher probability to obtain resources
Successful competitors survive and reproduce at higher rate
Higher proportion of individuals in next generation will have their traits
Evolution occurs when?
At the unequal reproductive success of individuals
How do you know when natural selection has occurred?
When the population adapts to its environment
What is phenotypic variation
Plasticity of characteristics
What is an example of genetic shift being an evolutionary process?
Smaller fish pass through mesh of gill nets and survive to reproduce, pass on genes for smaller size to their offspring
Example of genetic shift
Herds of elephants have a high proportion of members lacking tusks. Due to poaching, absence of tusks probably due to specific allele and not plasticity in tusk presence/size
What is human harvesting
Brings about rapid change in population traits
What was observed in human harvested populations?
Population traits shifted at rapid rates resulting in younger age/small size of reproduction
Changes may be evolutionary in?
Changes may be non-evolutionary in?
Is the environment ever constant?
No, the rate of change varies over time and place
Members of a population may experience environment change due to?
Movement to new environment
Shifts within environment
What are some recent shifts within the environment?
Global warming, human harvesting
What are some past shifts within the environment?
Continental drift, cold climates of ice age
When the environment first changes, what happens to the members of the population?
May not be as well adapted
Only inheritable traits can pass from one generation to the next
Acquired characteristics aren't inherited
Most traits don't possess a natural selective value
The favorable/unfavorable value of a trait depends on environment in which it occurs
Adaptive value of trait can change if environment changes
How does evolution result from natural selection?
Populations w/distinctive traits arise from ancestral populations lacking those traits
Over time different and distinctive populations have come and gone
What are some direct observations of evolutionary change?
Humans drive natural selection and population evolution
Evolution in natural populations
Examples of humans driving natural selection and population evolution
Insects to pesticides
Bacteria to antibiotics
Examples of evolution in natural populations
Plant population adaptation to extreme soils (population adapts to a specific type of soil, produces endemics)
Animal population adaptation to extreme conditions
Species which is unique to a place
What are fossil records?
The preserved traces of extinct organisms
What can fossils be used for?
Trace the origin of a group of organisms and the examination of changes that occur over time
What kind of evidence is provided by fossil records?
Change of life on earth over history of life
Contain more complex structures
Distribution of fossil in the earth layers
Coincides w/expected evolutionary result of increase in complexity of living organisms over time
Characteristics shared by a group of organisms which had a common ancestor
Basic similarity present but modification in structure reflect altered functions in the various descendants
What does homology represent?
The theme of descent w/modification
What are the 2 types of homology?
Structural and molecular homology
What is structural homology?
Structure has been modified for a variety of functions
What is an example of structural homology?
The limbs of vertebrates, especially the forelimbs
Terrestrial vertebrates all have the same basic forelimb bones
What is molecular homology?
Shared molecular structures of genetic material
Where was the genetic code originated?
The common ancestor of all living organisms
Define genetic code
The triplet of nucleotide sequences in DNA which code for the amino acids in a protein
Some genes are universally shared, retain similar functional properties in all types of cells
Some genes have similar molecular structure but different functional properties in different types of organisms
Geographic distribution of species
What occurs in biogeography?
Organisms move due to their own actions and due to movements of the continents
The observed distributions of current and extinct species matched the expected distribution based on evolutionary theory
What is an example of biogeography?
Species of large flightless birds found in South America, Africa, Australia and New Zealand. These birds are closely related even if they were found on different continents
A group of individuals of the same species that live in an area and interbreed and produce fertile offspring
Evolution results from?
Changes within a population
Natural selection acts on?
Individuals in a population
How do populations evolve?
The differential survive and reproduction of its members produces changes in population
Change within a population/species from generation to generation
Change in allele gene frequencies in population
Adaptation to an environmental factor
Changes of sufficient magnitude to produce new species
Observable form of trait in an organism
Pair of alleles for specific gene present in an individual
Formed of pairs of alleles
One allele of the gene comes from?
A gene determines a trait
Alternate alleles of gene produce different forms of trait
Example of heredity:
Garden pea plant flower color
: codes for the trait of flower color
: (P) - purple color, (p) - white color
Define population genetics
Study of the properties of genes in populations
What happens in a non-evolving population?
Each allele of a gene occurs at a certain frequency in the population
Example of non-evolving population:
Mosquito population of Mumbai, India before introduction of DDT
These frequencies remained constant through many generations
Non-resistance allele is unable to detoxify DDT
Resistance allele can detoxify DDT
1 allele resent in the cell
2 alleles present in a cell
What is the Hardy-Weinberg Principle?
Allele frequencies in a population which isn't evolving are unchanging frequencies of alleles and genotypes remain constant from generation to generation
What does the Hard-Weinberg Principle require?
A large populations w/random mating
No input of new alleles
What does the Hardy-Weinberg Principle equation describe?
The frequencies of the 3 genotypes formed from a gene w/2 alternate alleles
When the allele frequencies are in equilibrium
What is the Hardy-Weinberg Principle equation?
+ 2pq + q
What does p
describe in the Hardy-Weinberg equation?
Frequency of individuals w/2 copies of the more common allele
What does 2pq describe in the Hardy-Weinberg equation?
Frequency of individuals w/1 copy of each allele
What does q
describe in the Hardy-Weinberg equation?
Frequency of individuals w/2 of the less common allele
What is wrong with the Hardy Weinberg hypothesis?
Predicts no difference in the frequencies being measured
No factors are acting on the population to change the frequencies of the alleles
Some factor(s) are acting on the population to change the frequencies of the alleles
When can the Hardy Weinberg null hypothesis be accepted?
If from generation to generation the genotype and allele frequencies math those predicted by Hardy-Weinberg and remain unchanged
When can the Hardy Weinberg null hypothesis be accepted?
If after one or several generation, genotype frequencies don't match those predicted by the Hardy Weinberg equation
The mosquito example
Pre-DDT frequencies remained constant for many generations
Presence of a DDT resistance gene was unknown because natural selection factor wasn't introduced to the population
If environmental conditions didn't change, allele frequencies remained constant
DDT was introduced when environment changed, natural selection acted on individuals of population
Fittest individuals survived and reproduced (those w/resistance gene)
Hardy-Weinberg equilibrium was broken, gene frequencies changed
Microevolution occurred in mosquito population
What are the factors affecting the Hardy-Weinberg equilibrium?
Variation is produced in the population (mutation and sexual reproduction)
Allele frequencies are altered (natural selection, genetic drift, gene flow)
What is a mutation?
It's a change in the nucleotide sequence of the DNA
In an existing allele, may produce a new type of allele of the gene
The change in the nucleotide sequence may alter the way the trait is formed from that new allele of the gene
What is the ultimate source of new alleles?
When must a mutation occur?
In the potential germ cells (egg/sperm) to be passed to offspring and into the population
What do most mutations produce?
Alleles that are neutral (not changing the phenotype)
Alleles that are slightly/severely negative (producing a harmful phenotype)
Can mutant alleles be beneficial?
Yes, on rare occasions. Its phenotype makes the bearer better suited to the environment and enhances reproductive success
Over time and in large populations, alleles can produce favorable traits in their bearers, these are ultimate sources of variation in a population
How many mutations occur in cells?
1 mutation in every 100,000 cell divisions
How many mutations occur in germ cells?
Very few mutations
What happens during sexual reproduction?
Produces unique combinations of alleles in each individual
Formation of egg and sperm shuffles alleles of each parent into a unique set in the gamete
Union of egg and sperm produces new combination of allele pairs
What does fertilization bring together?
Gametes of individuals w/different genetic backgrounds
What provides a great genetic variation?
Mixing of alleles into new combinations in the individuals of a population
What does mutation and sexual reproduction both produce?
Genetic and phenotypic variation in the individuals of a population
Natural selection acts on the individuals of a population so that...?
Those individuals whose traits are best suited to the environment leave a higher proportion of offspring in the next generation
What does the environment determine?
Which types of individuals are fittest, these are the individuals "selected"
What does a gene flow do?
Transfers alleles into/out of a population
What is the result of a gene flow?
Change in allele frequencies of the population
What might a gene flow result from?
Migrations of individuals between populations
Movement of gametes
What happens when allele frequencies of a source population differ from a population to which the individual moves?
Frequencies of the receiving population may be changed
Example of gene flow in the mosquito,
: organophosphate (not DDT) was used for 30 years
In Europe, a mutation producing a resistance allele occurred in mosquitoes
The resistance allele spread rapidly due to long distance migration of mosquitoes (wind)
Each area became resistance, mosquitoes w/allele kept being blown to new areas
Much of the world's mosquitoes became resistance after introduction of resistance allele
Define genetic drift
Random change in allele frequencies in a population
What is the cause of genetic drift?
Where does genetic drift occur most often?
In small populations where events affecting a few individuals may have a large effect on the population
Example of genetic drift: founder effect
Few individuals are isolated from a larger population and establish a new population
Type and frequency of alleles in new population are a subset of the source population, may differ depending on allele combination occurring in the founders
Rare alleles and combinations of alleles may be present in new population
What are species?
A group of populations whose members are capable of interbreeding
Offspring are vigorous and fertile (healthy surviving offspring)
Reproductively isolated, can't produce fertile offspring w/individuals from different types of population (one kind of species can't reproduce w/another group)
All populations of the species are united by what?
Gene flow, this maintains their gene pool (individuals move from one population to another)
Explain the gene pool populations of a species
Consists of all the alleles for genes in all individuals of the population
The frequency of any combination of alleles depends on the frequency of each allele in the population
What happens if only one allele exists for a particular gene?
That allele is fixed in the gene pool, all individuals have 2 copies of that allele
What happens if two or more alleles exist for a particular gene?
Each individual may have any possible combination of these alleles
What is the biological species concept?
An effective way of understanding the existence of different types of species population in nature
What are some problems with the biological species concept?
Successful interbreeding can exist between different types of populations
Difficult to apply to populations which don't occur together
Many types of organisms are asexual, reproductive isolation doesn't apply
Why is it difficult to establish criteria for defining species?
There isn't a definite set of factors that maintain the identity of species in nature
What factors promote reproductive isolation?
Reproductive isolating mechanisms
Prezygotic isolating mechanisms
Separated in space, fertile at different times, incompatible behaviors, structural differences (doesn't get to zygote stage)
Postzygotic isolating mechanisms
Genetic incompatibility of the gene sets of the parents
Hybrids developing to some extent, but die as embyros/juveniles (no further development than zygote)
Hybrid adults are weak, vigorous, and sterile
What are prezygotic isolating mechanisms?
Factors preventing mating and fertilization (zygote --> fertilized egg, single cell, individual)
What are postzygotic isolating mechanisms?
Factors interfering w/proper development and reproduction of the offspring
What is speciation?
The formation of new species
2 populations of a single species diverge
Reproductive isolation forms w/each of the 2 new species
Population gene flow is altered and slowed, interrupted
What is allopatric speciation?
Populations become geographically isolated
Gene flow is restricted (cut off one species in population)
Gene pool of each population receives new alleles from mutation events
Genetic drift is small, isolated population may alter gene frequencies
What happens as the separated populations evolve?
Similarities decrease and reproductive barriers form
Where does speciation occur in sympatric speciation?
In populations that live in the same geographic area
What happens during sympatric speciation?
Gene flow is reduced between separating populations while their members remain in contact
Reproductive barrier develops and separates the 2 populations
What is an event that promotes sympatric speciation?
What happens in polyploidy?
Accidents in gamete formation in offspring w/increased number of sets of chromosomes (2+ sets of chromosomes)
Such offspring may be reproductively isolated from parental population
Where is it most common to find polyploidy to occur?
In plants, and sometimes animals
What is habitat differentiation?
A subpopulation is enabled to utilize a resource or habitat not used by the parental population