Natural Selection Flashcards
When does discontinuous variation in a trait occur?
when the phenotype is controlled by one or only a few genes, there are only a few possible phenotypes that fall into distinct classes
When does continuous variation in a trait occur?
when phenotypes do not fall into distinct classes, a continuous distribution of phenotypes (ex. eye colour)
What is a more common term for continuous variation?
quantitative variation, trait that has a quantitative value (ex. height, iq)
What are multifactorial traits? Example?
traits that are the result of the interactions between one or more environmental factors and two or more genes
ex. height is related to multiple different genes but it can be stunted by malnutrition
What type of phenotypic variation is subject to evolutionary change? Why?
genetically based phenotypic variation
it depends on differences in heritable traits
What is acclimatization?
adjusting to stress through behaviour or physiology
Does acclimatization occur to individuals or a population? Is it evolution? Why or why not?
happens to individuals
no it isn’t
b/c its a short-term, reversible process that happens to individuals
What is adaption?
any heritable trait that increases the fitness of an individual with that trait in a particular environment compared to others without that trait
Does adaption occur to individuals or a population? Is it evolution? Why or why not?
populations
yes
b/c its a long-term, genetic response of a population caused by natural selection
How are traits usually quantified?
measurement
What does the mean describe in terms of a characteristic in a population?
the average value of that characteristic in a population
What does variance measure?
the variability from the average or mean
What are the types of natural selection?
disruptive, directional, stabilizing, balancing
What is directional selection?
when natural selection move in one direction, changes the average value of a trait
What can directional selection lead to?
fixation of advantageous alleles and the loss of harmful alleles
What is stabilizing selection?
reduces the extremes of the population, no change in the average value of the trait being selected
What can stabilizing selection lead to?
decrease in genetic variation and a reduction in genetic diversity
What is disruptive selection?
favours the extremes of the population, opposite of stabilizing selection
What can disruptive selection lead to?
maintains genetic variation, average phenotype is eliminated, can lead to formation of new species
What is the difference between directional and disruptive selection?
directional moves towards one extreme in one direction (can be either extreme/direction)
disruptive moves towards both extremes in both directions
What is balancing selection? Example?
when multiple alleles are maintained in a population, genetic variation is maintained
heterozygote advantage
What is frequency dependent selection? Example?
form of balancing selection, where fitness is dependent upon the frequency of a phenotype/genotype in a population
negative frequency dependent selection: rare phenotypes hae higher fitness because they are eaten less
Will natural selection eventually lead to perfection?
no
Are adaptions universally good? Why or why not?
no, it increases their fitness in a particular environment so it isn’t universally good (environments can change)
What are fitness trade offs? Why does this happen?
compromises between traits in terms of the performance of these traits in a particular environment
selection acts on many traits at once, every adaptation represents a compromise between different selection pressures
What are some examples of fitness trade offs?
size of eggs/seeds and the number of offspring, rapid growth and long lifespan, bright colouration and attracting predators
Can natural selection eliminate all deleterious traits?
No, because heterozygotes and homozygous dominant organisms have the same phenotype and therefore the same fitness so the recessive deleterious allele will still be passed down
