Ch 23 Ap Bio
gene flow
-can introduce new alleles into the population -transfer of alleles into or out of population due to the movement of fertile individuals or their gametes -reduce genetic difference
p+q=_____
1
stabilizing
acts against both extremes
bottleneck effect
caused by severe drop in pop size where by chance alone, certain alleles may be over/under represented or absent altogether
genetic drift
chance events can also cause allele frequency to fluctuate unpredictably from one generation to the next, especially in small populations
microevolution
change in allele frequencies in a population over generations. ex: sparrow bird's body size evolving
gene pool
consists of all the alleles for all the loci in all individuals of the population
what are three mechanisms by which sexual reproduction shuffles existing alleles
crossing over, independent assortment of chromosomes, fertilization
q2
equal to the frequency of the homozygous recessive in the population
macroevolution
evolution on the grand scale over history
disruptive
favor individuals at both extremes
directional
favors one extreme, when pop's environ. changes or when members migrate to new habitat
what does the hardy weinberg proncipal state
frequencies of alleles and genotypes in a population will remain constant from generation to generation, provides that only mendellan segregation and recombination of alleles are at work
2pq
frequency of all the heterozygotes
which factor tends to reduce the genetic differences between populations and make new populations more smilar
gene flow
which factor results in random, non adaptive changes in allelic frequencies
genetic drift
effects of genetic drift
genetic drift is significant in small pop can cause allele freq to change at random can lead to loss of genetic variation w/i pop can cause harmfu alleles to become fixed
population
group of individuals of the same species that live in the same area and interbreed, producing fertile offspring
what does it mean to say that an allele is fixed
if only one allele exists for a particular locus in a population
sexual dimorphism
marked differences between the 2 sexes in secondary sexual characteristics. which arent directly associated with reproduction or survival such as size and color
intersexual selection
mate choice, indiv. of one sex (usually female), are choosy in selecting their mates fron other sex
what is the ultimate source of new alleles
mutation
what mechanism is the only one that is adaptive, or improves the match between organisms and their environment
natural selection
which results in individuals that are better suited to their environment
natural selection
what are three main mechanisms that can cause changes in allele frequency
natural selection, genetic drift, gene flow
what are the conditions for a hardy weinberg experiment
no mutations random mating no natural selection extremely large population size no gene flow
deviation from the hardy weinberg conditions...
potential cause of evolution
natural selection
results in alleles being passed to the next generation in proportions different from their proportions in the present generations
four reasons why natural selectin cant produce perfect organism
selection can only act on existing variations, evolution is limited by historical constraints, adaptations are often compromises, chance +natural selction+ environment interact
intrasexual selection
selection within the same sex, competing for mates from other sex
relative fitness
the contribution an individual makes to the gene pool of the next generation, relative to the contributors of other individuals
in hardy weinberg equation, p2 is equal to
the frequency of the homozygous dominant in the population
founder effect
when a few individuals become isolated from a larger population. this smaller group establishes a new population by whose gene pool differs from source
what are two ways of measuring genetic variation in a population
whole gene level (gene variability) molecular level of DNA (nucleotide variability)