12.1 Study Guide Flashcards
(9 cards)
Define natural selection. Explain why natural selection is not completely random.
Natural selection is the gradual change and alteration of a population’s overall phenotypes based on external, environmental factors. While some may think that natural selection and, as an extension, evolution, is completely random, the only part of the process that is random is the production of new traits through random mutation. Beyond this, natural selection is a passive but specific process that decreases the frequency of traits that produce disadvantageous phenotypes while increasing the frequency of traits that produce advantageous phenotypes. This occurs due to the increased likelihood of an organism with a disadvantageous phenotype dying before reproduction and not passing on its disadvantageous gene(s).
Define genetic drift. How is it different from natural selection?
While natural selection is mainly a non-random process, genetic drift is essentially entirely random. Genetic drift is the gradual change and alteration of a population’s overall phenotypes based on random chance. This randomness is produced by the random independent assortment of alleles during reproduction. Genetic drift occurs when one generation of a population randomly produces offspring with a much higher frequency of one trait compared to an equally advantageous trait, which may then produce future generations with higher and higher frequencies of the first trait until the second trait is basically removed from the gene pool.
Define biological fitness, variation, and adaptation. How are these three terms related in terms of evolution and natural selection?
Biological fitness is a measure of an organism’s ability to survive in its environment and is usually based on the organism’s traits/phenotype. Biological variation is the difference between the phenotypes of multiple members of the same population and is produced through recombination and mutation. Biological adaptation is the natural selection of a population’s genotypes and phenotypes due to newly introduced or encountered environmental factors that were not present before. Variation produced by recombination and mutation allows for adaptation, as new traits are able to be produced that are selected over others. Similarly, adaptation produced by variation and natural selection improves fitness, as advantageous traits that are selected over others inherently improve an organism’s and a population’s survival chances.
Explain differential reproduction. How is it connected to biological fitness?
Differential reproduction is a factor in natural selection and is the increased reproduction of members of a population with advantageous traits relative to those with disadvantageous traits. This produces more offspring with the advantageous traits than the disadvantageous traits each generation and gradually removes the disadvantageous traits from a population. By doing so, it grants the population and its members greater survival chances and, thus, increases their overall biological fitness.
State at least three of the five fingers of evolution. Explain how at least two affect a population’s gene pool.
Five fingers of evolution: 1. Population Shrinkage | 2. Selective Mating | 3. Mutations | 4. Gene Flow (immigration and emigration) | 5. Natural selection.
1. Population shrinkage is the spontaneous removal (usually death) of a large percentage of a population. By doing this, it can potentially massively change a population’s gene pool and affect how they will continue to evolve.
2. Selective mating is the tendency of members of a population to only mate with other members who have specific traits/phenotypes. This makes it difficult for certain traits to be passed on through the generations and can eventually remove them from the population.
3. Mutations are errors in DNA replication that can potentially produce new traits if they still produce cohesive genes. These new traits emerge slowly but can greatly alter a population’s genes and gene pool over time.
(I don’t really have space for the other two, sorry)
In a population, a dominant allele (G) of a specific autosomal gene gives members a survival advantage while a recessive allele (g) of the gene gives members a survival disadvantage. If the ratio of G : g begins at 1 : 1, explain how the frequencies of each gene will change over several generations and why. Will the recessive allele completely disappear?
As the generations pass, the frequency of the G allele will gradually increase, while the frequency of the g allele will gradually decrease. This is because offspring that happen to be born with two versions of the g allele will experience a survival disadvantage and will be less likely to eventually pass on the allele than offspring without the allele’s phenotype. This will slowly remove the allele from the population and make individuals with its phenotype much rarer. However, it is possible that the allele may not completely disappear, as it can be carried by some offspring but not expressed, and thus passed on silently throughout many generations.
In a population, a dominant allele (P) of a specific autosomal gene gives members a survival disadvantage while a recessive allele (p) of the gene gives members a survival advantage. If the ratio of P : p begins at 1 : 1, explain how the frequencies of each gene will change over several generations, what could happen to the population, and why.
Conversely to the previous example, as the generations pass, the frequency of the P allele will sharply decrease while the frequency of the p allele will sharply increase. This is because, as a dominant allele, the G allele will likely be expressed in the majority of the population, granting the majority of the population a survival disadvantage and causing them to die before reproducing and passing on the allele. If essentially every member of the population with the G allele dies before reproduction while essentially every member with two versions of the g allele reproduces and passes it on, the G allele will quickly disappear completely from the population and only the small number of g-expressing individuals will remain, sharply reducing the population’s size.
How might the effects of genetic drift differ between a smaller and a larger population?
Smaller populations are affected much more by genetic drift because, due to their small numbers, any difference in frequency between two genes/alleles will be quite high and will produce a speedy increase in one and decrease in the other. In larger populations, however, inherently large differences must exist to produce as quick of a result, and smaller, more common ‘drifts’ take very long spans of time to truly affect an entire population.
Explain how the causes and effects of natural selection are similar to and different from those of genetic drift.
The effects of natural selection and genetic drift are somewhat similar: One or several traits gradually increase in frequency within a population while their ‘partner’ traits gradually decrease, often until the increasing trait(s) are present in the entire population and the decreasing trait(s) are removed entirely. The primary difference between the two processes is how they occur/originate. Natural selection often requires random mutations to begin, but the process itself requires specific disparities in survival chances between members of a population based on differing traits, and it increases or decreases the frequencies of those traits accordingly. Genetic drift, however, does not require this disparity necessarily and is generally produced by random events that happen to cause one trait to increase and increase while another decreases and decreaes.
