Chapter 23 Flashcards
Natural selection acts on ________
individuals
_______ evolves
populations
this is a change in allele frequencies in a population over generations
microevolution
what two processes produce variation in gene pools that contribute to differences among individuals
mutation and sexual reproduction
these are the changes in the nucleotide sequence of DNA
mutations
where must mutations occur in order for them to be passed to offspring
in cells that produce gametes
this a change in one base in a gene and may or may not cause a mutation
point mutation
what types of chromosomal mutations are often harmful
those that delete, disrupt, or rearrange many loci are typically harmful
mutation rates are low in what kind of organisms
those with long life cycles
mutation rates are higher in what
organisms with short life cycles such as viruses
this is a localized group of individuals capable of interbreeding and producing fertile offspring
a population
this consists of all the alleles for all loci in a population
gene pool
what is required for a locus to be fixed
all individuals in a population must be homozygous for the same allele
what are the five conditions for nonevolving populations
no mutations, random mating, no natural selection, extremely large population, no gene flow
what are the three major factors that alter allele frequencies and bring about most evolutionary change
natural selection, genetic drift, and gene flow
this describes how allele frequencies fluctuate from one generation to the next, and often reduce genetic variation
genetic drift
this occurs when a few individuals become isolated from a larger population
founder effect
this is a sudden reduction in population size due to a change in the environment, such as a natural disaster
bottleneck effect
this consists of the movement of alleles among populations
gene flow
how does gene flow influence populations
reduces the differences between populations, more likely than mutation to alter allele frequencies directly
this is the only process that consistently results in adaptive evolution
natural selection
this is the contribution an individual makes to the gene pool of the next generation, relative to the contributions of other individuals
relative fitness
natural selection favors certain ______ by acting on the _______ of certain organisms
genotypes, phenotypes
what are the three modes of natural selection
directional selection, disruptive selection, and stabilizing selection
this type of natural selection favors individuals at one end of the phenotypic range
directional selectionth
is type of natural selection favors individuals at both extremes of the phenotypic range
disruptive selection
this type of natural selection favors intermediate variants and act against extreme phenotypes
stabilizing selection
this increases the match between an organism and its environment
adaptive evolution
why do genetic drift and gene flow not consistently lead to adaptive evolution
they are random, so they both increase and decrease the match between an organism and its environment
this is natural selection for mating success
sexual selection
this is marked differences between the sexes in secondary sexual characteristics
sexual dimorphism
this is selection within the same sex, individuals of the same sex compete directly for mates of the opposite sex
intrasexual selection
this is also called mate choice, individuals of one sex choose their mate from the opposite sex. It is usually based on showiness, or the male’s appearance or behavior
intersexual selection
in this, the fitness of a phenotype declines if it becomes too common in the population
frequency-dependent selection
this is when heterozygotes have a higher fitness than do both homozygotes
heterozygote advantage
this is genetic variation that appears to confer no selective advantage or disadvantage
neutral variation
examples of neutral variation
variation in noncoding regions of DNA, variation in proteins that have little effect on protein function or reproductive fitness
why can natural selection cannot fashion perfect organisms
selection can act only on existing variations, evolution is limited by historical constraints, adaptations are often compromises, chance, natural selection, and the environment interact
