Question

A large range of molecular markers can be used to assess population genetics. Why is it suggested that multi-loci and/or codominant loci are preferred over single loci? And why is mitochondrial DNA usually preferred over nuclear? How do the use of MHC data sets correlate?

How has phylogeographic analysis shown to be a useful tool in the investigation of whether populations are native or have been recently introduced into an area? Give two specific examples to help support the response.

Answer 1

Multiloci Markers are the Markers that represent various loci along the genome. e.g. RAPD (Random Amplification of Polymorphic DNA).

Single Loci Marker is a variation of alleles in one locus. Eg: RFLP (Restriction Fragment Length Polymorphism) marker is the single locus marker.

Multi-loci are preferred over single loci :

- RFLP is slow and tedious process and it also requires substantially larger sample sizes.

-RAPD technology provides a quick and efficient screen for DNA sequence based polymorphism at a very large number of loci.

- The main advantage of RAPD is that, it does not require pre-sequencing of DNA.

- RAPD has technical simplicity and it doesn't need any prior DNA sequence information.

- Mitochondrial DNA is an extra-chromosomal genome in the mitochondria of cell that is present outside of the nucleus, and is inherited from mother without paternal contribution.

-It has higher evolutionary rate than the nuclear genome, so this is used in studying phylogenies and knowing evolutionary history, and is therefore good for comparison inside species.

-MHC: ( Major Histocompatability complex) diversity has been observed as a possible indicator for conservation, because large, stable populations tend to display higher MHC diversity, than smaller, isolated populations.

Phylogeography : It is the study of the early processes that may be lead to geographic distributions of species. This is done by considering the geographic distribution of individuals according to genetics, more specifically population genetics.

Events taken into considerations are:

-population expansion

-population bottlenecks (massive decrease in the size of a population due to events such as famines, earthquakes, floods, fires, disease, and droughts or human interference)

-migration

Example :

-glaciation cycles of the past 2.4 million years, has restricted many species into disjunct refugia. These restricted ranges resulted in population bottlenecks that reduce genetic variation. Once a reversal in climate change allows for rapid migration these species will spread rapidly into new favorable available habitat.

-Also, imperiled cave crayfish in the Appalachian Mountains of eastern North America showed this phylogeographic effect.