How sympatric, allopatric speciation and nonrandom mating differs?

Speciation Two ways in which speciation can occur. Allopatric speciation occurs when a gene pool is geographically divided into two Sympatric speciation occurs without geographic separation of the populations.. Allopatric speciation Occurs when a population is divided by a barrier. Can occur because a barrier develops or because some members of population disperse to a new area. Once separated, the gene pools diverge as each population adapts to its local environment. Over time isolating mechanisms are likely to develop. If after many generations members of the allopatric populations are brought back together they may or may not be able to produce fertile offspring. Even if they can do so, those offspring may have intermediate characteristics which suit them to neither of the parental environments and thus they will be selected against. Allopatric speciation If intermediates are selected against, we would expect isolating mechanisms (barriers to reproduction) to be strongly favored by selection. Ultimately the two populations would become different enough to be unable to interbreed successfully and so become new species. Allopatric speciation Examples. Two species of closely related antelope squirrels live on opposite sides of the Grand Canyon. The canyon is a barrier to their dispersal. In contrast, birds and other species that disperse well have not undergone speciation on opposite sides of the canyon Different Galapagos Islands contain different species of finches, which have evolved in the approximately 2 million years since the islands were first colonized from the South American mainland. Allopatric speciation Diane Dodd investigated development of reproductive barriers in fruit flies. Raised populations for several generations on either starch or maltose medium. Fly populations diverged each becoming better at digesting its food source. Allopatric speciation When flies from “starch populations“ and from “maltose populations“ brought together they were significantly more likely to mate with flies of their own population. Sympatric Speciation Indicates that reproductive barriers between species can begin to form quickly. In sympatric speciation, speciation takes place in geographically overlapping populations. Mechanisms of sympatric speciation include polyploidy and nonrandom mating that reduces gene flow. Polyploidy is common in plants and many species have resulted from accidents in cell division that produce extra sets of chromosomes. For example a diploid plant (2n chromosomes) may become a tetraploid (4n). The tetraploid cannot produce fertile young with diploid plants because young will be triploid (3n chromosomes), but can self-pollinate or mate with other tetraploids. Sympatric Speciation Polyploidy can thus result in speciation in just one generation. Polyploidy can also occur when two different species produce a hybrid. The offspring are often sterile because chromosomes cannot pair up during meiosis. However, the plant can often reproduce asexually. Subsequently, various mechanisms can convert a sterile hybrid into a fertile polyploid called an allopolyploid. The allopolyploids are fertile with each other, but not other species and so are a new species. Many important crops are polyploids. For example, the wheat used for bread is an allohexaploid (six sets of chromosomes, with two sets from each of three different species). Sympatric Speciation Non-random mating. Reproductive isolation can occur when genetic factors enable a subpopulation to exploit a resource not used by the parental population. Sympatric Speciation Example: North American apple maggot fly. Original breeding habitat was hawthorn fruits on hawthorn trees, but about 200 years ago some populations colonized apple trees. Apples mature faster than haws (hawthorn fruit) so apple-feeding flies have been selected for rapid development. Sympatric speciation in apple-maggot flies Natural selection favors divergence because hawthorn fruits ripen 3-4 weeks after apples. As a result, hawthorn fly larvae experience cool temperatures before pupating whereas apple fly larvae experience warmer temperatures. Hawthorn flies and apple flies thus depend on different temperature signals to time their pupation and emergence the next spring and have different developmental timetables. Apple-feeding flies now temporally isolated (isolated in time) from hawthorn-feeding flies. Speciation appears well underway. A protein electrophoresis study by Feder et al. (1988,1990) showed that the two populations are genetically distinct. Sympatric Speciation Lake Victoria cichlids. Lake Victoria about 12,000 years old but home to more than 500 species of cichlids (fish). #Cancer #ExplainEverything #gene #explain #geneExpression #GeneticsLecture #everything #GeneticExamQuestionsSolutions #geneticCode #chromosome #GeneticsExamQuestionsSolutions #genetics #genotype #Iherb #DNA #GeneticTesting #molecularBiology #gene