BIOL Chapter 24 - The Origin of Species
gen bio 155 sem I
Terms in this set (45)
mystery of mysteries
speciation to Darwin
the process by which one species splits into two or more species. results in diversity and similarity.
changes over time in allele frequencies in a population
the broad pattern of evolution above the species level
Latin for "kind" or "appearance"
biological species concept
a species is a group of populations whose members have the potential to interbreed in nature and produce viable fertile offspring with members of other such groups, but do not. Absence of gene flow.
the existence of biological factors (barriers) that impede members of two species from interbreeding and producing viable fertile offspring. blocks gene flow and prevents hybrids.
offspring that result from an interspecific mating
impede mating or hinders fertilization if mating does occur
what are the 3 ways prezygotic barriers act?
1. impede members of different species from attempting to mate
2. preventing an attempted mating from being completely successful
3. hindering fertilization if mating is complete successfully
what are the prezygotic barriers?
two species that occupy different habitats within the same area may encounter each other rarely, if at all, even though they are not isolated by obvious physical barriers, such as mountain ranges
ex. terrestrial, aquatic
species that breed during different times of the day, season, years, etc and cannot mix their gametes
ex. certain flowers pollinate in fall, others in spring
courtship rituals that attract mates and other behaviors unique to a species are effective reproductive barriers, even between closely related species. such behavioral rituals enable mate recognition
ex. females like the showiness and colors of a male peacock's feathers more than another male
a way to identify potential mates of the same species
mating is attempted but morphological differences prevent its successful completion
ex. genital openings are not aligned in two species of snails
sperm of one species may not be able to fertilize the eggs of another species, sperm gets lost in reproductive tract of females, other spring prevent sperm from penetrating the membrane surrounding the other species' egg
ex. when urchins release sperm and eggs into surrounding water, they do not always fuse and form a zygote because of the openness of the mating area
prevent a hybrid zygote from developing into a viable fertile adult
what are the postzygotic barriers?
-reduced hybrid viability
-reduced hybrid fertility
reduced hybrid viability
the genes of different parent species may interact in ways that impair the hybrid's development or survival in its environment
ex. hybrid's do not complete development and can be weak and frail
reduced hybrid fertility
hybrids that are strong but are sterile because the chromosomes of the two parent species differ in number or structure, meiosis in the hybrids fail to produce normal gametes. when infertile hybrids mate they cannot produce offspring and genes cannot flow freely between species
ex. donkey + horse = sterile mule
some first generation hybrids are viable and fertile, but when they mate with on another or with either parent species, offspring of the next generation are weak or sterile
ex. strain of cultivated hybrid rice that accumulates mutant recessive alleles
morphological species concept
characterizes a species by body shape and other structural features, applies to sexual, and asexual and useful with or without information of gene flow. subjective and used the most.
ecological species concept
views a species in terms of its ecological niche, the sum of how members of the species interact with nonliving and living parts of their environment, accommodates sexual and asexual, emphasizes role of disruptive n.s. as organisms adapt to different environment conditions
phylogenetic species concept
defines a species as the smallest group of individuals that shares common ancestor, forming one branch on the tree of life
what are 2 ways speciation can occur?
gene flow is interrupted when a population is divided into geographically isolated subpopulations, can occur without geologic remodeling. repoductive barriers formed in isolated population can prevent interbreeding even if rejoined with parent population.
speciation occurs in populations that live in the same geographic area. descendants can become isolated from parents in a remote area. can occur when gene flow is blocked from isolated population.
sympatric speciation occurs by gene flow being reduced by what 3 factors?
2. habitat differentiation
3. sexual selection
species may originate from an accident during cell division that results in an extra set of chromosomes. occurs occasionally in animals, most prevalent in plants. very rare, but many crops are this way.
an individual that has more than two chromosome sets that are all derived from a single species
fertile polyploid when mating with each other but can't interbreed with either parent species, this occurs when two different species interbreed and produce sterile hybrid offspring. most are sterile because the set of chromosome can't pair during meiosis with the set of the other one it is trying to pair with.
sympatric speciation can also occur when genetic factors enables a subpopulation to exploit a habitat or resource not used by the parent population
sympatric speciation can also be driven by mate choice of female based on male breeding characteristics. male coloration is main reproductive barrier that normally keeps the gene pool of these two species separate
Incomplete reproductive barriers come in contact. region in which members of different species meet, and mate, producing at least some offspring of mized ancestry
formation of hybrid zone
1. Populations connected by gene flow.
2. Barrier to gene flow formed.
3. Population diverges from others
4. Gene flow re-established in a hybrid zone.
what are 3 possible outcomes for hybrid zones over time?
1. reinforcement barriers
2. fusion of species
process involving reinforcing reproductive barriers, strengthens the reproductive barriers and reproductive isolation, usually stronger in sympatric populations. hydrids gradually cease.
fusion of species
so much gene flow occurs that reproductive barriers weaken and gene pools of the two species in hybrid zone become increasingly alike that lead to the two hybridizing species to fuse into a single species
hybrids continue to be produces occurs because hybrids survive or reproduce better than members of either parent species at least in certain habitats or years and the narrowness of hybrid zone because members of both parent species migrate into the zone from the parent populations located outside the zone and keep on creating hybrids
describes periods of apparent stasis punctuated by sudden change. speciation occurs rapidly.
total time between speciation?
Time that elapses before populations of new species start to diverge + time it takes for speciation to complete.Varies considerably.
1. On average it takes millions years for new species to form
2. Only begins after gene flow is interuppted.
3. Once interuppted populations must diverge to become reproductivley
isolated before gene flow can resume.
Genes required to influence evolution?
Few or many
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