Evolution Exam 2 Study Guide Questions And Answers

What is genetic variation? - ANS Traits that are inherited from the parents, genotype. i.e. skin tone was inherited by parents, eye color What is environmental variation? - ANS The environment dictates the expression of a trait. i.e. tanning in the sunlight. What is genotype-by-environment interaction? - ANS The results are due to differences in the genes that were inherited from their parents. i.e. one friend tans while the other burns Should you make your child eat broccoli? Why might people that cannot taste PTC eat more vegetables? - ANS Because broccoli is good for you. People that have the PAV/PAV allele on the TAS2R38 taste receptor are more likely to dislike broccoli and its relatives, because they taste more bitter and are more sensitive to the toxins, those than cannot taste PTC have the AVI/AVI allele are the least sensitive to the toxin that is produced by the broccoli and family. This mean vegetables taste better to them compared to those that can bind PTC strongly. PTC isn't found normally in food, but there is a correlation to the ability to taste it and how the tAS2R38 responds differently to other bitter flavors. What happens when Daphnia pudges smell phantom midges? - ANS When the water flea is exposed to the phantom midges kariomone the water fleas produce a nearly double the strength and thickness of its carapace and they grow ridges. This is called their "neck teeth". This is a response to the chemical change in its environment - defense mechanisms. Environmental variation. Does environmental variation lead to evolutionary change? - ANS No, environmental variation supplies no raw material for evolution, environmentally includes change in phenotype are not transmitted to future generations. Whether the water flea was born by clonal reproduction has neck teeth is determined not by the genes it inherits, but by the presents or absence of kairomones. Except the concept of epigenetics. Computing Consequences 5.1: Do epigenetic marks significantly contribute to long-term evolution? Why? - ANS Epigenetic marks serve at least three functions. 1. They silence transposons, integrated viruses and other genomic parasites. 2. They allow individuals to communicate with their offspring, and sometimes their grand-offspring, useful information about the state of the environment they are likely to encounter. 3. And in multicellular organisms, they facilitate and maintain cell differentiation. The latter 2 functions require that epigenetic marks be periodically reset. This may explain why many epigenetic marks induced by the environmental factors appear programmed at some point int he life cycle or to decay over several generations. Do not contribute to long-term evolution. How is sex determined in leopard geckos? Are temperature that induce change always the same in all leopard geckos? - ANS The individual's sex is determined largely by the temperature at which it incubates while developing in the egg. Geckos that incubate in cool or hot temperatures are females and those that are in an intermediate temp are males. No, they are not always the same. They will differ from gecko to gecko. The pattern of phenotypes an individual may develop upon exposure to different environments is called reaction norm. The reaction norms are based on the genes given to the offspring by fathers. This is an example of genotype-by-environment interaction. Define phenotypic plasticity. - ANS An organism that develops different phenotypes in different environments. Populations harbor genetic variation for environmental sensitivity, populations can evolve greater or lesser plasticity. How do you get black tobacco hornworm caterpillars to turn green? - ANS You expose the black caterpillars to high temperatures shortly before molting. After the heat shock they emerge from molting with a green coloration. Some were insensitive to the heat shock, still emerging black. The variation in sensitivity is an example of genotype-by-environment interaction. Where do new alleles come from? Briefly explain the different mechanisms. - ANS New alleles arise from alterations to existing alleles by mutations. Mutations creating new alleles can arise as a result of alterations to DNA that escape repair before or during replication, or because of errors that occur during replication itself and escape repair afterword. DNA alteration - if a C gets altered and turns into a T - then the replication will produce a compliment T-A on the mutated strand - changing that DNA base pair. DNA can become misaligned especially when there is multiple of the same base pair in a row, this results in the insertion or deletion of nucleotides. If it evades repair before the next replication, it will become permanent in one of the daughter cells. What are premutations, and are they common? - ANS DNA alterations that are still susceptible to repair, they are appallingly common. A typical mammalian cell suffers roughly 20,000 cases of spontaneous chemical decay in its genome daily. And 100,000 replication errors per division. DNA polymerase has effective repair mechanisms, so a majority of these mutations are not passed on. Why could a mutation that changes CAA to CAT lead to a silent mutation? - ANS CAA and CAT codons GUU and GUA code for the same amino acid, Valine. This leaves the encoded protein unaltered. Are all nonsense mutations in humans deleterious? - ANS Nonsense mutations arise when a mutation causes a premature stop codon. This often renders the encoded protein nonfunctional, but some happen late in the gene, causing not too big of an issue. A nonsense mutation does provide an advantage for endurance athletes. How is "immigration delay disease" manifest? - ANS There is a mutation at the splice site that can prevent introns from being spliced out before translation. This causes the introns (intervening sequences) from being excised from the exons (coding sequences). This results in added RNA this is translated into proteins. The splice-site mutation that causes adermatoglyphia - the absence of fingerprints. Where do now genes come from? What are the two most common mechanisms for gene duplication? - ANS Many mechanisms generate new genes - two mechanisms of gene duplication (existing genes) are thought to be among the most common sources of new genes. 1. The first is unequal crossing over, an error in the genetic recombination that happens during meiosis. In normal crossing over, homologous chromosomes (from mom and dad) align side by side during prophase of meiosis I and exchange stretches of DNA containing the same loci. In unequal crossing over, the homologous chromosomes align incorrectly. This happens in nucleotide repeat heavy regions in one place on the chromosomes. The consequence of misalignment is that the DNA segments exchanged are out of register, on chromosome ends up with a duplication and the other ends up with a deletion.