48 terms

H Bio Rossi- Everything you need to know about Ch. 13- How Populations Evolve

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theory of evolution
- created by Darwin
- theory that earth's species are descendants of ancestral species
- Wrote On the Origins of Species by Means of Natural Selection
- Descent with modification
Jean Babtiste Lamarck
- proposed that if a species doesn't use a body part, and individual may lose it and therefore change
- "change" can be passed onto offspring
adaptions
diverse modifications based on changes in the environment
natural selection
"survival of the fittest"
artificial selection
modification of a species by selecting and breeding individuals with specific traits
How many observations and Inferences are there that support natural selection?
2 observations
2 inferences
Observation #1
members of a population often vary in their inherited traits
Observation #2
all species are capable of producing more offspring than the environment can support
Inference #1
Individuals whose inherited traits give them a higher probaility of surviving and reproducing in a given environment tend to leave more offspring (stronger traits are passed onto offspring)
Inference #2
this unequal production of offspring will lead to an accumulation of favorable traits in a population across generations
Pete and Rosemary Grant
- Compared the beak sizes of Finches
- Observed that large beaks thrived in the dry season where there were larger seeds to eat and small beaks thrived in the wet season when there were smaller seeds to eat
Fossils
- not the actual remains but instead a "mold" of the organism
fossil record
- sequence in which fossils appear in layers of sedimentary rock
- forms strata (layers)
4 Supporting Reasons for Evolution
1. biogeography
2. comparative anatomy
3. comparative embryology
4. molecular biology
biogeography as a support for evolution
- biographic distribution of species
- migration from one place to another (new species arise or form but resemble species in other locations)
comparative anatomy as support for evolution
- anatomical similarities between species
- homology
- homologous
- vestigal structures
homology as comparative anatomy
similar characteristic that result from common ancestry
homologous as comparative anatomy
features that have different functions but similar structure
Ex: human arm, bat wing, fin, cat leg
vestigal structures as comparative anatomy
"left over" features that served an important function in the organism's past
Ex: appendix, tail bone
comparative embryology as support for evolution
comparison of the early stages of development
Ex: vertebrates
molecular biology
- compare DNA of organisms
- homologous genes with similar sequences
population
- a group of individual of the same species that live in the same area and interbreed
- look for evolution via changes in traits of a certain species
gene pool
total collection of genes in a population at any one time (all of the alleles)
mutations
- a change fo the normal nucleotide sequence of DNA
- usually not a good thing
- Rare: for mutant allele to improve the genome
sexual reproduction in terms of genetic variation
where most genetic variation occurs from the combination of alleles in the offspring
3 Random components of sexual reproduction:
1. Crossing over
2. Independent assortment of chromosomes
3. Random fertilization
Hardy- Weinberg Principle
- the genotype frequencies in a population will remain constant from generation to generation
*Review the homework worksheet for this
5 requirements for Hardy Weinberg to be true
1. Very large population
2. No gene flow between populations
3. No mutations
4. Random mating
5. No natural selection
* Basically, this is impossible to achieve
microevolution
- random/rare events
- 3 Main methods of microevolution
1. Natural selection
2. Genetic Drift
3. Gene flow
Natural selection
- for Hardy Weinburg to be true, all individuals would have an equal change to reproduce
- never happens in nature
Genetic Drift
- smaller the sample, more of a deviation from ideal result
- large populatiions, more reliable/consistent
In Genetic Drift chance events cause allele frequencies to fluctuate unpredictably from 1 generation to another. Smaller the population, larger the effect on genetic drift. Name the 2 types of events that can cause the frequencies to fluctuate
Bottleneck Effect
Founder effect
Bottleneck Effect
- drastic reduction in population
- Earthquake, flood, fire
- genetic drift may continue for many generations until the population builds back up
Founder Effect
- genetic drift that occurs when a small set of individuals found a new habitat
- smaller the group, the less likely to represent the larger population
E.G.: Blind colony
Gene Flow
- individuals leave or enter with different genetic makeups
Balance of Variation (4 Types)
1. polymorphic
2. balancing selection
3. heterozygote advantage
4. frequency dependent selection
polymorphic
population where there are 2 or more forms of a characteristic
balancing selection
occurs when natural selection amintains stable frequencies of 2 or more phenotypes
heterozygote advantage
possible explanation for balanced polymorphism
heterozygous reproduction is more common
frequency dependent selection
the survival and reproduction of any 1 form declines if the phenotype becomes too common
Stabilizing selection
favors intermediate
Directional Selection
favors 1 phenotypic extreme
common during periods of environmental change
Disruptive selection
"middle falls"
favors both ends of a phenotypic range
Sexual selection
form of natural selection in which individuals with certain traits are more likely to obtain mates
sexual dimorphism
- distinctions in appearance
- height
- peacocking
- more common in males
intrasexual selection
- when individuals compete directly with members of the same sex
e.g.: physical combat
intersexual selection
- individuals of one sex are choosy in selecting mates
- usually females
- male attracts
- these displays of affection can put the couple at risk
4 Reasons why Natural Selection cannot make the perfect organism
1. Selection can only act on existing variations
2. Evolution is limited by historical constraints (new anatomical features come from existing features)
3. Adaptions are often compromises
4. Chance and natural selection interact (genetic drift and environmental changes)