Transcript populations
G. RANDOM CHANGE IN A POPULATION Evolution happens with populations, not individuals We say that a population has evolved when it is different from the original population in its allele frequency or genetic make-up This difference in genetic make-up results from specific alleles being passed on to the next generation in a nonrandom pattern 1. Genetic Drift in small populations, alleles can be lost at random from the population eg. if there are two populations each with a rare allele at a frequency of 1% in one population of 50,000 [500 have it] and in another population of 500 [5 have it] if some random event kills 20 % of the population it may kill the 5 who have it, but is unlikely to kill all of the 500 in the larger population 1b. Bottleneck Effect this is a large, usually temporary, reduction in the population that usually results in a significant genetic drift eg. there were once 100,000 elephant seals but we hunted them by the 1890’s there were only 200 elephant seals now there are 30,000 elephant seals and all are descended from the 200 so much genetic diversity was lost eg. cheetahs were once captured by Romans to use as hunting pets they killed so many cheetahs capturing them, that the population went through a bottleneck now if we do skin transplants among these cheetahs, all East Africa cheetahs accept foreign tissue which implies limited diversity with South African cheetahs, we see lots of rejection implying diversity 1c. The Founder Effect this results when a small population colonizes a new area, again causing a limited number of alleles to be present which is a form of genetic drift eg. in the 1971 five adult pairs of lizards were moved to a new island in the Mediterranean Italian wall lizard the old island had sparse vegetation and many insect species to eat the new island has dense vegetation and many fruits species to eat the lizards have been on the island for only 36 years but now they have larger heads with bigger chewing muscles also an enlarged pouch in their intestine for bacteria that break down cellulose 2. Gene Flow often animals live in isolated colonies however, once a year, males are driven out of the home colony and move to a new colony [eg lions] depending on the species, females may be driven out instead [eg bees] in either case, these individuals bring their alleles with them and will likely alter the genetic balance in the new colony Published online: 28 April 2007; Climate change alters genes on the fly Global warming is influencing the genetics of fruitfly populations. The 'S' version of Adh seems to encourage survival in hot, dry conditions. Hoffman's team sampled the flies in 2006, and found that the distribution of AdhS had shifted some 400 kilometres south from where it was two decades earlier. Therefore we can see that global climate change can directly affect the alleles in a population. 3. Mutation the random process of making changes in alleles themselves most mutations appear to be neutral [no visible change] or harmful, but a very few will be beneficial Mutation is not random! Genes that contains the sequence TATA in its promoter are more likely to have evolved than that of a genes that do not have TATA in its promoter. 3b. Gene Duplication a segment of a chromosome or a single gene is accidentally duplicated during DNA replication this duplication has no immediate effect, positive or negative Possible benefits of gene duplication the organism now has a spare copy of a gene so that when a change is made, in the duplicate a working copy remains if the change produces a less useful protein, the organism still has the original and so does not suffer if the change produces a more useful protein, then organism directly benefits On to selection Choanoflagellates are single-celled zooplankton that diverged from animals 500 milions years ago. They have five immunoglobulin domains, though they have no immune system; They have collagen, integrin and cadherin domains, though they have no skeleton or matrix binding cells together; and proteins called tyrosine kinases that are a key part of signaling between cells, even though Monosiga is not known to communicate, or at least does not form colonies.