Prelim 1 Flashcards
Evolution and Human Variation - lectures 1-9
Evolution
Change in a gene’s relative frequency in a population over time
Species
A population of individuals that interbreed and produce fertile offspring
Microevolution
Small changes within a species over time
Macroevolution
Major changes in a species’ form or behavior which categorize it as a new species
Natural selection
A mechanism through which small changes in a population accumulate into huge ones; increased frequency of traits that help individuals survive and reproduce
How does natural selection work?
- Limited resources -> competition to survive and reproduce
- Individuals in populations vary
- Inheritable traits that give an advantage will increase in relative frequency
Allopatric Speciation Model
Populations speciate after growing geographically isolated and being affected differently by natural selection
Character displacement
Populations sharing a geographic area adapt to different niches so they no longer compete
Types of reproductive barrier between species
Post-mating (offspring infertile or unhealthy) & pre-mating (form, lifestyle, mating activity too different to interbreed)
Biological Species Model
Species = population of individuals that interbreed and produce fertile offspring
Ring Species
Groups of neighboring pops. in which adjacent species can interbreed, but those at either “end” can’t
Hybrids
2 populations look and act totally different but can bear fertile offspring with unique “hybrid” traits
Evolutionary Species Concept
Use morphology to determine who is descended from whom
Phylogenetic Model
Examine groups to find a shared evolutionary history
What are the challenges to the Biological Species Model?
- Ring species
- Hybrids
- Paleobiology
How does speciation happen?
- A group within a population separates from the rest, usually geographically
- Natural selection decreases the prevalence of some traits and increases others
- Species can no longer interbreed with the original/divergent pops.
Nucleic Acids
Chains of nucleotide bases - DNA, RNA
Proteins
Chains of amino acids which perform varied functions
Which organisms have DNA?
- Viruses
- Prokaryotes
- Eukaryotes
DNA
Double-stranded macromolecule made of nucleotides which carries genetic information
Nucleotides
Organic molecules made up of a nucleotide base (A, T, C, G) and sugar
Gene
Section of DNA with instructions to make a protein
Chromosome
Large package of DNA stored in cell nuclei
Locus
Location of a gene on a chromosome which remains constant for whole species
Karyotype
Map of all your chromosomes
How is DNA turned into a protein?
- Transcription: one DNA strand is copied onto messenger RNA (mRNA)
- Translation: RNA is turned into amino acids (three nucleotides make up one AA)
- End result: chain of amino acids form a protein
What are the sources of variation in sexual reproduction?
- Crossing-over: every round of meiosis, a little bit of each chromosome may switch over
- Independent assortment: different pairs of alleles separate independently from each other
Alleles
Different versions of a gene that may vary at loci
Homozygous
Identical alleles for a trait
Heterozygous
Different alleles for a trait
Dominant allele
Will always create its protein
Recessive allele
Will be blocked from creating its protein by dominant allele (only produces if homozygous)
Codominant alleles
Two alleles that always produce their protein
Phenotype
Observable traits, e.g. eye color or blood type
Why isn’t all variation eliminated through generations?
Explanation: Traits are particulate - may “disappear” but reoccur in future generations, & combine but do not blend or change through genetics
Proof: plant experiments
Gene pool
Abstraction of all genes present in a population
Population
Group defined for a situation (usually a breeding population)
4 causes of evolution
- Mutation
- Migration/gene flow
- Genetic drift
- Natural selection
Mutation
Change in a gene’s actual chemical structure
Types of mutation
- Chromosomal aberrations -changes in structure/number of chromosomes which are very destructive and affect many genes
- Point mutations - changes in a single nucleotide in a DNA change
* May result in FRAME SHIFT - changes all proteins
Gene flow (migration)
Movement of individuals
Genetic drift (def & causes)
Chance changes in gene frequency, esp. in smaller populations, due to:
1. Random removal of alleles in meiosis
2. Founder Effect - small subset forms new group with higher frequency of certain genes
3. Inbreeding - reduces randomness, increases chance of rare recessive diseases
Fitness
Reproductive success - how many genes an organism passes on, or how many (grand)offspring it has relative to others
Subspecies
A genetically distinct population of a species which may or may not be speciating
What are the assumptions behind race-IQ claims?
- Human “races” = subspeciees
- Each human has general intelligence measurable by a #
- That number can be objectively measured with a test
Discordant variation
Variation that doesn’t match up - e.g. features used to determine “race” don’t map onto each other consistently
Heritability
Proportion of total phenotypic variation caused by genetic variation (WITHIN a group) vs environmental variation
H = ?
H = VG / (VG + VE)
Clines
Relatively regular change in a biological trait (aka allele frequency) over geography
How can we know if a trait is or was adaptive?
If clinal variation in the trait correlates strongly with variation in an environmental stressor
Why is dark skin advantageous near the equator?
Melanin protects against UV rays:
1. Decreased risk of skin cancer from high UV exposure
2. Overdose of vitamin D -> kidney failure
Why is pale skin advantageous near the poles?
Less melanin means absorbing more UV rays
1. Vitamin D needed for healthy bones and childbirth
Heterozygote Advantage
Individuals benefit from heterozygote alleles when multiple selective forces act
E.g.: malaria is less successful on sickle cells, but sickle cells are unhealthy -> benefit to having one healthy allele and one sickle allele
Adaptation
Degree to which an individual can utilize its environment as a result of natural selection on its ancestors
Acclimatization
How an individual responds to environmental changes within its lifetime
Developmental Acclimatization
Physiological changes from being born + growing up in certain extreme conditions
