Ch22 and Ch23 Flashcards
adaptations
inherited characteristics of that enhance their survival and reproduction in specific environments
natural selection
a process in which individuals that have certain inherited traits tend to survive and reproduce at higher than other individuals because of those traits
artificial selection
human selection of organisms
Darwin’s observations and inferences
- members of a population vary
- all species can produce more offspring than their environment can support and many die
- better suited individuals produce more offspring
- this leads to an accumulation of favorable traits
homology
similarity resulting from common ancestry
homologous structures
similar structures due to common ancestry
vestigial structures
remnants of features that served a function in the organisms ancestors
convergent evolution
the independent evolution of similar features in different lineages
analogous features
shared features due to convergent evolution
endemic
found nowhere else in the world
microevolution
evolutionary change in populations, smallest scale of evolution, change in allele frequency over generation
genetic variation
differences among individuals in the composition of their genes or other DNA segments
discrete character
either -or trait;normally single gene locus
quantitative character
trait that varies along a continuum; normally two or more genes
average heterozygosity
the average percentage of loci that are heterozygous: quantification of gene variability
geographic variation
differences in the genetic composition of separate poppulations
cline
graded change in a character along a geographic axis
poppulation
a group of individuals of the same species that live in the same area and reproduce
gene pool
all copies of all alleles in a poppulation
Hardy-Weinberg principle
the frequencies of alleles and genotypes in a population will remain constant from generation to generation, provided that only Mendelian Segregation and recombination of alleles are at work: the resulting gene pool is a Hardy-Weinberg equilibrium
conditions for Hardy-Weinberg
- no mutations
- random mating
- no natural selection
- extremely large population size
- no gene flow
genetic drift
chance events that cause alleles to fluctuate unpredictably, especially in small populations
founder effect
a new population separate and different from the original population
bottleneck effect
severe drop in population that causes certain alleles to survive by chance
genetic drift key points
- significant in small populations
- can cause allele frequencies to change at random
- leads to a loss of genetic variation
- can cause harmful alleles to become fixed
gene flow
the transfer of alleles into or out of a population
relative fitness
the contribution an individual makes to the gene pool of the next generation relative to the contributions of others
directional selection
conditions favor one extreme; directional shift; mice getting darker
disruptive selection
favor individuals at both extremes; white and black mice
stabilizing selection
favors intermediate variants;all brown mice
sexual selections
traits passed on by acquiring mates
sexual dimorphism
gender difference
intrasexual selection
selection within a gender (normally male)
intersexual selection
select from other gender (normally female)
neutral variation
differences that do not give advantage or disadvantage
balancing selection
when selection maintains two or more forms
heterozygote advantage
when being heterozygous is advantageous
frequency-dependent selection
when fitness is dependent on commonality
4 reasons perfect organisms are not formed
- selection can only act on existing variations
- evolution is limited by historical constraints
- adaptations are often compromises
- chance,natural selection, and the environment interact.
