Mechanisms of Evolution Flashcards
What are mechanisms of evolution?
Mechanisms that change allele frequencies
In a species of fruit fly, Drosophila subobscura , DNA inversions common to high (northern) latitudes occur less frequently at low latitudes, and vice versa. In nearly all sites where the flies have recently been sampled (a span of three continents) the frequency of low-latitude inversions have crept upward. Flies in sites with a temperature increase of half a degree Celsius have the pattern of inversions that 30 years ago existed in flies 70 miles closer to the equator. What is this type of mech. of evolution?
Natural selection because a genetic feature confers an environmental advantage to some of the individuals, which are then most fit.
Researchers found that Tibetan mothers who are able to store more oxygen in their blood have more offspring that live to maturity. In the low-oxygen group, each woman had on average 2.5 children that died during childhood. In the high-oxygen group, that average was just 0.4. It was also determined that this trait was inherited in a way that suggested the difference was due to a single gene. What type of mech of evolution is this?
Natural selection. It suggests that a gene dictating the level of oxygen in the blood confers a reproductive advantage (the ones with this gene can more easily reproduce and spread the gene through the population).
Atherosclerosis is principally a disease of the modern age, one produced by modern diets and modern life-styles. There is a community in Italy near Milan whose residents don’t get atherosclerosis because of a fortunate mutation in one of their forebearers. This mutation is particularly interesting because the person who had the original mutation has been identified. What is this mechanism of evolution?
Mutation. It suggests that a new allele is responsible for a disease. However, this disease does not hinder reproduction for carrier individuals. Hence, there is no reproductive advantage and it can not be natural selection.
The US National Health and Nutrition Examination Survey, published by the National Center for Health Statistics (NCHS) on 27 October, 2004, presents trends in estimates of mean weight, height and body mass index of adults from 1960 to 2002.The main finding of the study is not contested. The weight of the average American is increasing alarmingly: the average for both men and women has increased by 11 kilograms over the past 40 years. But the NCHS also publicized a second conclusion: “Adult men and women are roughly an inch taller than they were in 1960.” What type of mechanism of evolution is that?
None. The increase in height can be due to air pollution, health, nutrition, etc. It is not something genetic, so it cannot be considered as evolution because there is no effect on allele frequencies.
Andrew McAdam, at the University of Alberta, Canada, and colleagues monitored four generations of squirrels in the Yukon, Canada, over 10 years. They found that female squirrels now give birth on average 18 days earlier in the year than their great-grandmothers. What type of mechanism of evolution is this?
Natural selection. We see that there is a reproductive advantage in here.
Polydactyly – extra fingers or sometimes toes – is one symptom of Ellis-van Creveld syndrome. The syndrome is commonly found among the Old Order Amish of Pennsylvania. In the Amish, in fact, Ellis-van Creveld syndrome has been traced back to one couple, Samuel King and his wife, who came to the area in 1744. The mutated gene that causes the syndrome was passed along from the Kings and their offspring, and today it is many times more common in the Amish population than in the American population at large. What type of mech. of evolution is this?
Genetic drift (due to the founder effect). The Amish population started as a small population in a new habitat. They carry a small sample random alleles from the original genetic pool. They are not representative of the whole population.
All of the cattle on Iceland are descended from a small group that were brought to the island more than one thousand years ago. The genetic make-up of the Icelandic cattle is now different from that of their cousins in Norway. What type of mechanism of evolution is this?
Natural selection or genetic drift. We talk about a small population being established in a new habitat (founder effect). There is also the fact that the environment in Iceland may be different and thus confer them a fit advantage.
The Panama Canal links the Rio Chagres and Rio Grande rivers. When the Panama canal opened, the once-isolated fish communities of the two rivers were given the chance to intermingle. The Rio Grande has gained five freshwater species that previously lived only in the the Rio Chagres, and three species have spread in the opposite direction. What type of mechanism of evolution is this?
None. We know that new species are created, but we have no clue whether the allele frequencies have changed within the populations.
Bacteria have been found that can metabolize short nylon oligomers, breaking the nylon linkages with a couple of related enzymes. Since the bonds involved aren’t found in natural products, the enzymes must have arisen since the time nylon was invented (around the 1940s). What type of mechanism of evolution is this?
Mutation. We talk about a new protein, so we think about new genes… and that comes from mutations!
Although phenotypes in the premodern world were more geographically bound than they are today, race is not geographical. What is meant is that people take their genes and their cultural preferences and tendencies with them. One portable tendency is to marry someone similar to ourselves. Sociologists call this tendency homogamy. It is through the practice of homogamy that similar phenotypic traits are replicated by cultural selection. What type of mechanism of evolution is this?
Non-random mating. (Although it is not a mechanism of evolution per se) It is suggested that the mates were chosen.
Is evolution always random?
Although most of the mechanisms are random, natural selection is not random (bc. there is a selection). So it is not always random.
Where does mutation need to occur if it is to be considered as a mechanism of evolution?
IN germ-line cells. If it is in somatic cells, mutations will not be transferred to other generations.
What is a source for new alleles and the base for genetic diversity?
Mutations. However, it is sometimes not significant in changing allele frequencies at the beginning when it is new.
What is gene flow?
It is the movement of alleles (of individuals) between distinct existing local populations.
Gene flow = gametes that move
Migration = Individuals that move
Random
