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chapter 17 pop. genetics and evolution (population genetics (gene pool …
chapter 17 pop. genetics and evolution
population genetics
population concept of species
character, ranging of values, Adult height: 1 m to 2.5 m skin color: white, brown, black, yellow, ect., blood type A, B, AB, O. similar ranges of variation occur in all species, and it's just as true of plants as it is of us.
type concept of species
biologists and others thought in terms of one single ideal specimen-- the type--that would represent a species. the concept had several foundations
gene pool
founder individual
all offspring greatly resemble the first
founder
the initial gene pool is extremely small; if just one seed is the founder, the original gene pool consistes of its two sets of alleles
genetic drift
convergent evolution
if two distinct, unrelated species occupy the same or similar habitats, natural selection may favor the same phenotypes in each. as a consequence, the two may evolve to the point that they resemble each other strongly
although the population is small, it is more subject to accidents, and thus, the gene pool can change rapidly and erratically
total number of alleles in all the sex cells of all individuals of a population
artificial selection
natural selection
purpose, intention, planning
or voluntary decision making
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natural selection does not include these
speciation
divergent speciation
reproductively isolated
gene flow does not keep the species homogeneous throughout its entire range, divergent speciation may occur; if alleles that arise in one part of the range do not reach individuals in another part
abiological reproductive barrier
allopatric
the original species In species is physically divided into two or more populations that cannot interbreed; if speciation results
or geographic speciation
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any physical, nonliving feature that prevents two populations form exchanging genes
biological reproductive barrier
sympatric speciation
when two groups become reproductively isolated even though they grow together
prezygotic isolation mechanisms
prevent pollen form moving from one plant to another, and thus, neither pollination nor fertilization occurs
postzygotic internal isolation barriers
hybird sterility
two populations occasionally interbreed or are artificially cross-pollinated and produce viable seeds, but the seed grows into a sterile plant
hybrid inviability
if cross-pollination occurs, alleles form one parent may code for proteins incompatible with those coded by alleles form the other, and not even a sterile hybrid can result; instead, the zygote or embryo dies early in development
separate two subpopulations that are considered separate species
any biological phenomenon that prevents successful gene flow
adaptive radiation
millions of years are often required for a species to evolve into a new one
phyletic speciation
gene flow
occurs in many ways, such as by pollen transfer, seed dispersal, and vegetative propagation
which one species gradually becomes so changed that it must be considered a new species
natural selection has caused a new species to evolve
the most significant factor causing gene pool changes, is usually described as survival of the fittest
the process in which humans purposefully change the allele frequency of a gene pool
deals with the abundance of different alleles within a population and the manner in which the abundance of a particular allele increases, decreases, or remains the same with time
chemosynthesis
second atmosphere
because hydrogen is such a light gas, most of this first atmosphere was lost into space
reducing atmosphere
all of these are found in vocanic gases and in meterorites that still strike earth. molecular oxygen was absent; it had already combined with other elements, resulting in compounds such as water and silicates
oxidizing atmosphere
only after all of the free iron in eath's oceans had oxidized did oxygen finally begin to accumulate in the atmosphere. the atmosphere present today was derived from the early second atmosphere by this addition of oxygen from photosynthesis
the most seriously considered hypothesis about the origin of life on earth; basically, the chemosynthetic hypothesis attempts to model the origin of using only known chemical and physical processes, rejecting all traces of divine intervention