Lecture Twenty Four - Evolution II Flashcards
What concept did Mayr come up with?
The biological species concept - species are being reproductively isolated from one another.
Defines a species as members of populations that actually or potentially interbreed in nature, not according to similarity of appearance.
Although appearance is helpful in identifying species, it does not define species.
Limited as it does not refer to asexual reproduction.
What is pre and post zygotic isolation?
Pre-zygotic isolation - impedes matin or fertilisation between different species.
Post-zygotic isolation - results in hybrids that are inviable or infertile.
How do reproductive barriers work with reproductive isolation?
Begins with strong gene flow between populations.
Then after some isolation, there is some gene flow, but it is weak.
Then reproductive isolation (but may be imperfect in ‘young’ species (that is, species who have just split recently)).
What genetic factors dictate whether or not speciation occurs?
How many genes are involved in isolation? (Are there on-locus ‘speciation’ genes, or must many genes diverge?)
Where in the genome are genes for reproductive isolation located? (In a few linkage groups, or dispersed thoughout the genome?)
What is the mode of action of these genes (what do they do)?
How can selection lead to the spread of an ‘incompatibility gene that causes reduction or total loss of fitness?
What are the different kinds of speciation?
Allopatric speciation - Biological populations of the same species become vicariant
- isolated from each other to an extent that prevents or interferes with genetic interchange.
This can be the result of population dispersalleading to emigration, or by geographical changes such as mountain formation, island formation, or large scale human activities (for example agricultural and civil engineering developments).
Parapartic speciation - The relationship betweenorganisms whose ranges do not significantly overlap but are immediately adjacent to each other; they only occur together in a narrow contact zone.
Sympatric speciation - The process through which new species evolve from a single ancestral species while inhabiting the same geographic region.
What is a ring species?
A connected series of neighbouring populations, each of which can interbreed with closely sited related populations, but for which there exist at least two “end” populations in the series, which are too distantly related to interbreed, though there is a potential gene flow between each “linked” population.
Such non-breeding, though genetically connected, “end” populations may co-exist in the same regionthus closing a “ring”.
What is polyploidy?
Polyploid cells and organisms are those containing more than two paired (homologous) sets ofchromosomes.
Most eukaryoticspecies are diploid, meaning they have two sets of chromosomes—one set inherited from each parent.
However, polyploidy is found in some organisms and is especially common in plants.
In addition, polyploidy also occurs in some tissues of animals that are otherwise diploid, such as human muscletissues. This is known asendopolyploidy.
