As we know, chromosomes
alterations in human being have usually negative effects, causing diseases,
sterile individuals or even death.
However, many species not only survive with these alterations but they
can evolve from them. These alterations are a type of mutation, which is source
of changes in the genome, leading to genome evolution (Reece et al., 2011). I
going to explain how some types of chromosome alterations contribute to the
evolution: Polyploidy (widely common in plants and rare in animals) and alterations
of chromosome structure.
Duplication
of entire chromosome sets is result of accidents in meiosis that produce
diploid gametes. According to Freeman and Herron (2004), if an individual self-fertilize
its produced male and female diploid gametes, it will originate a polyploid organism.
If this organism can self-fertilize or mate with another poplyploid, it is established
a tetraploid population. This event is
important in evolution because if the tetraploid population mates with their parental
diploid population, they will originate triploid organisms, which are sterile due
to the odd number of chromosome set. Therefore, this leads to branching off of
a new species. Also, the extra sets can accumulate mutations that promote new
functions of the extra genes, maintained by natural selection (Freeman and
Herron, 2004). These events change the individual phenotype and the new
population diverges further from their parental population.
Another
contribution to evolution is observed in alterations of chromosome structure. Researchers
have noticed chromosome rearrangements comparing a species to another. For
example, ancestral chimp chromosomes 12 and 13 seem to have fused end to end,
forming the chromosome 2 of a human ancestor. Comparing some species,
scientists find many duplications and inversions of large portions of
chromosomes, as result of DNA breaks and incorrect rejoining during meiotic
recombination. These events might have accelerated about 100 million years ago,
contributing to the generation of new species (Reece et al., 2011).
REFERENCE LIST:
Freeman, S. & Herron, J.C. (2004) Evolutionary Analysis. 3th ed. Pearson Prentice Hall. United States
of America. p 124.
Reece, J. B.; Urry, L. A.; Cain, M. L.; Wasserman, S. A.;
Minorsky, P. V.; Jackson, R. N.(2011) Campbell
Biology. 9th ed. Pearson Australia Group. p 446.
Chromosomal alterations are very interesting. Can you provide an example of an organism that is polyploidy? Do humans show any alterations in chromosome structure within the species, as well as between humans and primates? These two topics are great areas for future research as there are so many unanswered questions.
ReplyDeleteYes. Nearly hald of all angiosperm species are polyploid. One example is the plant species Hibiscus rosa-sinensis.
ReplyDeleteThere is chromossome alterations in humans usually causing diseases or even cancers. An example is the syndrome Cri du Chat (Cry of the Cat), a deletion in chromosome 5. As I said at the last paragraph, it is seen some evidences of chromosome structure during evolution from primates to humans.
I may talk more about the effects of these alterations on phenotype later.