Flashcards in Topic 1 - Species Deck (23):
Explain the phylogenic species concept
Defines a species as a group of organisms that are descended from a common ancestor and that all possess defining characteristics which distinguish them from other such groups.
The evolutionary process whereby new species arise. Speciation causes one evolutionary lineage to split into two or more lineages.
Define the biological species concept.
Defines a species as a group of actually or potentially interbreeding populations, which are reproductively isolated from other such groups.
Define reproductive isolation.
Occurs when reproductive barriers prevent or strongly limit successful reproduction between populations with the result that there is little or no gene exchange between them.
Explain gene flow
The transfer or incorporation of genes into the gene pool of one population from one or more other populations. Gene flow occurs only if reproduction follows the dispersal of an individual or gamete to a new population.
The existence within a population of two or more discrete phenotypes within a population. In the simplest case each phenotype results from different alleles of a single gene. In more complex cases the phenotype results from interactions between many different genes and the environment.
List some problems with the biological species concept
Hybrids can result from species considered separate. The term 'potentially interbreeding' is problematic. Some natural populations experience hybrid zones. It can't be applied to asexual organisms.
Define 'hybrid zone'
A geographic zone where genetically distinct natural populations come into contact and hybridise. Many hybrid populations exhibit a continuum of variation, spanning the gap between parental populations.
Conceptual representation of the history of evolutionary relationships between given organisms, usually depicted as some form of tree-like diagram showing the sequence (and sometimes absolute dates) of branching events between divergent descendants.
Explain the difficulty with the phylogenic species concept.
Morphology is highly subjective and can change over time. For example the alterations as a triceratops matures meant that juveniles were once considered a separate species.
What are the most widely accepted species concepts?
Biological species concept and phylogenic species concept.
Explain the key step in the evolution of new species
when populations become reproductively isolated from one another by barriers that prevent the exchange of alleles between them.
Explain geographical isolating barriers
mountain ranges, rivers or any other feature of the environment, which are extrinsic to the organism and keep populations apart by physically preventing them from mixing and interbreeding.
Explain reproductive isolating barriers
intrinsic features of the organisms themselves and which minimise the chance of interbreeding between individuals of different populations.
Define allopatric speciation.
Speciation in which the evolution of reproductive isolating barriers occurs during physical separation of the populations.
Explain reinforcement in terms of speciation.
The evolution of reproductive isolating barriers as a result of natural selection against maladaptive hybridisation between two diverging populations that have been geographically isolated from each other for some time and then come back into contact again (also known as secondary contact)
Define sympatric speciation.
Speciation in which the evolution of reproductive isolating mechanisms occurs when populations inhabit the same geographic locality.
Explain hybrid incompatibility.
A postzygotic form of reproductive isolation in which hybrids between species are inviable or sterile.
Explain hybrid break down
A postzygotic form of reproductive isolation in which an interspecific hybrid is viable or fertile, but subsequent generations are not.
Populations of a species that show geographic variation in morphology and that may differ genetically but that can interbreed.
What are speciation genes?
Genes that are involved in maintaining reproductive isolation between species or contribute to the cessation of gene flow between populations.
A horse has 64 chromosomes while a donkey has 62. How many chromosomes would a mule and a hinny have and how many of these would be inherited from each parent?
Mules and hinnies both have 63 chromosomes. Mules inherit 31 chromosomes from the male donkey and 32 from the female horse; hinnies inherit 32 chromosomes from the male horse and 31 from the female donkey.