Unit 3 Flashcards
In 300 BC, it was thought that…
Life forms are permanent and unchanging
In the 1600’s, the date of creation was taken from…
the Bible (4004 BC).
In the 1800’s, it was discovered that…
Earth’s geological phenomena are due to gradual natural causes that we can still observe. Therefore Earth must be millions of years old. Current estimates > 4 billion.
Before Darwin, who suggested that species evolve?
Charles Lyell, Erasmus Darwin and Jean Baptiste Lamarck
What did Larmack propose?
an evolutionary mechanism: species adapt to their environment
- Traits change through use or disuse
- Acquired changes are passed on to offspring
*no evidence to support inheritance of acquired traits
Explain Darwin’s observations of the cacti on the Galapagos islands…
Cacti on the Galápagos Islands with tortoises were
taller than those on other islands because the tallest
cacti were less likely to be completely eaten, and
therefore left more descendants
Explain the three premisses of which the theory of evolution by natural selection rests…
Darwin realized natural selection is the mechanism by which populations adapt to their environment. The concept of natural selection rests on three premises:
1. Every species is capable of producing more offspring than can survive or reproduce
2. Individuals in a population have heritable variation in traits affecting their chances for survival or reproduction
3. Individuals with the most advantageous traits will
produce the most offspring
Define evolution…
- Cumulative change in the genetic characteristics of a population or species through time
- Change in allele or genotype frequency over time
Define natural selection…
The process by which the genotypes genetically best
suited to survive and reproduce in a particular
environment give rise to a disproportionate share of the offspring and so gradually increase the overall ability of the population to survive
Explain the premises by which evolution by artificial selection rests…
Darwin realized natural selection is the mechanism by which populations adapt to their environment. Artificial selection works in a similar way:
1. Species are capable of producing more offspring than humans choose for further breeding
2. Individuals in a population have heritable variation in traits affecting their chances of being chosen.
3. Humans ensure that individuals with the most
advantageous traits will produce the most offspring
Natural selection is ____ ______ ________ of evolution.
only one mechanism
*Natural selection ≠ Evolution
What forces lead to evolutionary change?
- Mutation
- Genetic drift
- Natural selection
- Non-random mating
- Migration
Define genotype frequency…
- Proportion of a population with a certain genotype
Define allele frequency…
- Proportion of gene copies of a certain type (allele) in the population
Define population…
All individuals of a certain species living in a particular area
Define polymorphic…
Multiple different alleles at a locus
Explain the process of predicting phenotypes and genotypes.
True breeding lines are crossed
(PP and pp) —>
All F1 have purple phenotype
(genotype is Pp) —>
Cross (or self) F1s
(Pp and Pp) —>
F2 show 3:1 purple:white phenotype
F2 show 1 PP : 2 Pp : 1 pp genotype
Define locus…
the position of a gene on a chromosome
Define allele…
any of the alternative forms of a given gene (P or p)
Define genotype…
the genetic constitution of an organism (PP, Pp, pp)
Define phenotype…
the observable trait (purple or white flower)
What is a mutation?
- Mutation is the ultimate source of all heritable variation in evolution
- Any change in the DNA of an organism
- Mutations occur randomly as a result of mistakes in
replication or during crossing over - Mutations can be induced by chemicals or radiation
- Only mutations that occur in reproductive cells are
heritable
Explain the types of mutation…
Substitution (cta –> cAa)
Insertion (cat –> caGt)
Deletion (cat –> c-t)
Explain the affects of mutation on phenotype…
- In plants and animals, most mutations have little or no effect on phenotype
- When there is a phenotypic effect, it is usually bad
- Occasionally, mutations have a good effect on
phenotype
Explain the relation between mutation and evolution…
- Mutation is the ultimate source of all heritable variation in evolution
- Point mutations at a site are rare: about 1 in a billion
- Therefore (on their own) new mutations do not change allele frequencies much
- When populations are extremely large: most possible mutations might occur somewhere
Define random genetic drift…
Random changes in allele frequency
*Chance events can lead to large changes in allele
or genotype frequency when populations are small
*this is NOT natural selection
Explain past genetic drift: the founder effect
- Colonization of new area by a small part of original population
- Causes reduced genetic variability
*Yellowish flowers (with R 1) could have survived just as well.. this is not natural selection
Define fitness…
The ability of an organism to… survive and transmit its alleles to the next generation
What are the components of fitness?
- Viability: Survivorship from fert. to repro.
- Fecundity: The # of offspring produced
- Viability and fecundity lead to # of alleles transmitted to the next generation
*More alleles contributed = Higher fitness - this leads to adaptation = the process by which a population changes phenotype to one that better fits the present environment
What was Mendel’s first law?
law of segregation: Two alleles at a locus segregate
into separate gametes: half carrying one allele and the other half the other
Explain directional selection…
Individuals with an extreme phenotype are… favored over individuals at the other extreme
Example: Weedy plants on islands
- Dispersal –> “drowning”
- Strong selection against dispersal
Explain stabilizing selection…
Stabilizing Selection: Favors individuals with… intermediate phenotypes
- Results in a narrowing of
phenotypic distribution
- Avg value remains
unchanged
Explain disruptive selection…
Disruptive Selection: Intermediate trait values are
disfavored, extremes favored
- Results in: Phenotypic divergence
Define outbreeding…
mating between distantly related parents
Define migration…
movement of individuals from one population
to another
Define gene flow…
movement of alleles from one population to
another through mating
Define hybridization…
movement of alleles from one species to another. Hybridization is not very common.
What happens when there is no gene flow?
Populations diverge until they are too different genetically, phenotypically or ecologically to mate: Speciation
Explain convergent evolution…
Adaptation to similar environments can cause unrelated species to evolve similar traits
Explain morphological species concept
Organisms are considered members of the same species if they are highly similar in morphology (appearance)
*early taxonomists
Explain the biological species concept
Species are groups of interbreeding natural populations that are reproductively isolated from other such groups
What are some problems with the biological species concept?
- Does not apply to asexual organisms, which include
many microbes and some plants - Difficult to apply or test
- Hybridization: many species (especially plants) can
interbreed at least a little with other species
*That is why scientists also use many other species
concepts
Define allopatric variation…
geographic isolation resulting in genetic divergence
Define sympatric variation…
genetic divergence without geographic isolation
Examples of geographic variation include…
- Formation of new islands
- Examples of geographic barriers
- Recession of glaciers
- Fragmentation of habitat
- Drying down of a water body
Explain polyploidy…
Polyploids contain more than 2 sets of chromosomes
- Found in some animals
- Very common in plants
- In some tissues e.g. liver cells of mammals, endosperm of plants
Most crops are ________.
polyploidy
Polyploid plants have _______ ______ and tend to be _______ plants.
larger cells; larger
Explain sympatric speciation via polyploidy…
Two distinct species produce a fertile hybrid with increased ploidy – it cannot mate with either parent species so a new species has formed
Define allopolyploidy…
two distinct species produce a fertile hybrid with increased ploidy
Define autopolyploidy…
Chromosome doubling within a species
Explain the process of allopolyploidy…
- Two species cross
- Pairing problems during meiosis in hybrid
- Chance chromosome doubling
- Every chromosome now has a partner
- Fertility is restored
*The allopolyploid has more chromosomes than parents, so crossing with parent species leads to sterile offspring (problems pairing in meiosis)
Explain the process of autopolyploidy…
- Nondisjunction in meiosis
- Diploid gametes fuse —> Tetraploid (4N)
*The tetraploid cannot exchange genes with the diploids because: Offspring will have odd number
of chromosomes so pairing in meiosis fails
What is allopatric speciation?
Allopatric speciation
* species diverge when separated by geographic
barriers
What falls under sympatric speciation?
Sympatric speciation
* Allopolyploidy
* Autopolyploidy
* Other mechanisms e.g. non-random mating,
ecological isolation, disruptive selection
Define taxonomy…
the branch of science concerned with classification, especially of organisms; systematics.
Explain how to write scientific names…
There is a correct way to write scientific names. It follows a ranked system developed by botanist, Carl Linnaeus in 1700s:
1. Every species has a unique name.
2. All names follow a two-word (binomial) convention.
- Generic name (noun)
- specific epithet (adjective)
–> Conveys info about the spp.
3. Names are in Latin. –> non-changing
Define phylogenetics…
the study of evolutionary relationships among species
Define morphology…
the physical structure of an organism
* Morphology is strongly affected by natural selection to fit the organism’s environment
DNA sequence is better for phylogenetics because…
- The discovery of protein and DNA sequences showed that some proteins and their genes changed extremely slowly.
- Their differences reflect degrees of relatedness.
