Study Guide Chapter 13 #3 Flashcards
struggle for existence
all living things are engaged in what charles darwin called a ……, involves phsyical traits
natural selection
may be sruvival of fittest but fitness is more than simply brute strengthes
fitness
relative contribution that an individual makes to gene pool of next generation
phenotype
exposed to envrionement NOT GENOTYPE
diploid
each individaul has two sets of chromosomes and two genes for each character
genetic variation
hidden alleles consititue a reserve of genetic varion, keeping gene pool from becoming too reform
balancing selection
possible for natrual selecction to maintain both alleles in gene pool,
heterozygous advnatage
main yellow allele in gene pool heterozygous red flowers coudl have some advantage over both homozygous red and yello forms - improved diseased resistance
frequency dependent selection
type of balancing selection, maintains two different phenotypic forms in population by selecting aginst either form if it become too common,
netural variation
much of genetic variation in population probably has little or no impact reproductive success
sexual dimophosim
natural selection often shapes differences in appearance
seconardy sexual characteristics
might be used in fighting over females
intrasexual selection
invovles mate choice, seconardy sexual characteristiics might be used to fight over females
males
display their bright plumage
females
do choosing
good genes hypothesis
a long tail, or loud mating call might reflect overall male health
natrual can act
three different ways in which natural selection can act on variation in a poplulation
characteristics
such as height vary continuously and can be describd by a bele shaped curve
stabilizing selection
kind fo natural selection, favors intermediate variants, not too tall and not too short
directional selecction
tyep of natural selection, might favor those individuals geneticaly programmed to grow deepest roots, most common during periods of envrionement change
diversing selection
occurs when two different sets of enviornmental conditions favor extreme phenotypes and act against interpedent types
natural selection
can only act on exisiting variations which depend on history and chance
adaptions
often compromises
examples of stabiliing selection
few very short platns in popuatiion and majority of plants of medium heights and few very tall plants, imagine our wildflowers gowing in cold windy environment and very tall plants might freeze before their seeds mature, shorter plants would stay warmer, but very short plants might have troulbe dispering their seeds ot favorable envrionment, STABILIZING SELECTION FAVORS INTERMEIDATE VARIANTS NOT TOO TALL NOT TOO SHORT
example of directional selection
environemnt is gradually becoming drier, DIRECTIONAL SELECTION MIGHT FAVOR THOSE INDIVIDUALS GENETICALLY PROGRAMMED TO GROW THE DEEPEST ROOTS
example of diviersing selection
(ample, plants with shallow, spreading roots might be an advtange in dry s=rocky soil where water tends to penetrate quicly and deep taproot system might be gavored in richer soul that hodls water longer, intermate root systems would be at disadtanvte in both enviornemtns)
