User:Shellynjeri/sandbox/Biology assessment

Lesson 8: Question 1: Differences in phenotypes that influence the probability of survival or reproduction (S) and differences in phenotypic traits that must be at least partially heritable. Natural selection is not the same as evolution. That is, you can have natural selection without having a population evolving if, h 2 = 0. It means that selection can be estimated independently of whether there is a response. For example, you might count up how many individuals in a population with a certain trait value die in this generation as one estimate of selection for or against that trait. The estimate of selection is called the selection differential, S, and it is the difference the trait means of individuals that successfully reproduce individuals versus the trait mean of the general population. In order to calculate natural selection only two variables are required, the heritability and the number of individuals selected for in a population. Question 2: Adaptedness shows how far a population is on its climb up to fitness. The closer the population is the more fit it is. The crossbill bird is a bird that feeds on cones. The crossbill birds are situated in different places, with different types of cones. Natural selection has made the traits of the birds to be different to suite the type of environment they are living in and the type of conifer trees. Each trait confers differently for the birds depending on the shape of the cone. Given a situation where by, ac cross bill bird is used to feeding on the Douglas Fir is moved to an environment where there are only Weston Hemlock conifers tree then the bird will start feeding on the WH. It is so because, as time goes by the birds will start getting traits that will help them adapt to the new source of food. This will cause changes to their beaks as they will evolve to help them become more adapted to the WH conifers. This enables the birds to be highly fit hence achieving peak fitness in the ecological niche. However, it is not the case for the WH birds. This is because the birds cannot be adapted to eating the conifers from the DH plant. It is so because, the birds have a beak depth of about 8.0 and a beak grove around 1.7. Any individual who varies from those means will be selected against. Thus, to get from WH to DF, the population would have to cross a “fitness valley” where trait combinations that are less fit somehow survive and reproduce. This is unlikely. Thus, the population is stuck on a local peak, and can’t get to the global peak. It won’t switch resources. This will Make the birds to be selected against and unfit making the DH birds more fit for survival and reproduction than the rest. Question 3: Immigration: Birds from DF adapted populations could introduce alleles that add phenotypes to the focal population that are favored to evolve to the DF peak. However, they’d have to “jump” to the DF mountain at a point where they have higher relative fitness than birds at the WH peak. It would be so likely to happen if the bird of WH were to mate with the birds of Dh. This would cause the next generation to acquire the traits of the DH causing them to be adapted to feeding on both the WH conifers and the DH conifers. Mutation: It is possible, though very unlikely, that one or several mutations could introduce the required phenotypes for adapting to DF. Mutation is a random process and can be triggered by the environment or other factors. Mutation will be beneficial as they will enable the WH birds to acquire traits that will make them more adapted to eating DH conifers. Small mutation on the WH birds would results in to them becoming more adapted to eating DH conifers. Environmental change: The figure above suggests that the landscape is static. However, in many cases, adaptive landscapes are dynamic. One could imagine that the above landscape is only for times of drought stress where cones are limited. In that scenario, it might be important to be efficient at seed extraction. However, during times of plenty, where cones are readily available, perhaps efficiency doesn’t matter. All birds are well fed, regardless of phenotype. In this scenario, there wouldn’t be a selective punishment for being a bird with intermediate phenotype. The “ruggedness” of the landscape reduces, and more phenotypic combinations have similar fitness. In this way, birds might be able to cross the fitness valley because the valley itself disappeared with environmental change. When drought returns, the population could find itself on the foothill of the DF peak, and in that way, evolve to use DF. When food is in plenty and all the birds are well fed, then the WH conifers will not require to adapt to new food. But when there is drought or les food the birds will have to adapt to new ways of feeding. This is to ensure that they increase their chances of survival and that they are not selected against by natural selection. Question 4: Evolutionary constraint. The answer is that the largescale fitness peaks and valleys formed early in the history of life, such that any lineage that tried exploring new biological modes would enter fitness valleys, and therefore been selected against. The Meganuera is a type of insect which resemble and related to the dragon fly. This insect, however are extinct. This is due to the fact that the insect had large bodies and it was difficult to transplant oxygen through out the entire body unless oxygen was sufficient in the environment where they were. As time went by the insects tried to mutate or to adapt to the new environments which caused them to enter into a fitness landscape hence rendering them extinct. Question 5: Another adaptive hypothesis: Alleles that cause small size in juveniles are favored by natural selection because small size tends to be associated with cuteness, and may therefore trigger more parental care, increasing survival probability of the juvenile. It is also a way for them to win the love of older people hence they are taken care of and looked after in a special hence increasing their chances of survival. Adaptive hypothesis is not applicable in this case. It is so because it doesn’t make any sense for an individual to give rise to an offspring that is bigger than itself. This mainly applies to organisms that carry the juveniles inside of them. There is no way an individual can carry a being that is twice its size in its body. It would be at a high risk of bursting and dying, killing both itself and the unborn baby. It can’t be larger than you if you have to birth it. It also applies to the individuals that lay eggs to reproduce as they would have produced larger garments and feed those offspring’s a tone. Even if the juveniles would be born big, they would later on shrink and become small. This would cause them to age backwardly instead of growing bibber they end up getting smaller and smaller. In this case we argue with the facts and reality, it is unnecessary to bring in the adaptive hypothesis. However, this does not apply to all organism’s as tsetse flies and other blood sucking individuals lay eggs that are twice their weight. Question 6: Independent assortment and genetic recombination (crossing over) have the potential to change a focal allele’s genetic context during meiosis. That is, allelic combinations found in gametes might be different than allele combinations found in the parent. This can happen due to inversion, deletion of replication of a gene locus. This may cause some genes traits that are not present in the parents to be seen in their offspring’s. Sex has the potential to change a focal allele’s genetic context when egg and sperm fuse to make a new individual. That is, allelic combinations found in offspring might be different than allele combinations found in the parents. The phenotypic effects of genes whose alleles behave in a dominant/recessive way is context dependent, meaning that the effect of an allele might change depending on the other allele in the genotype. This applies when one of the alleles is most prominent in an individual. An example is when the blue and brown eyes individual. When one of the parent’s eyes are blue and the other is brown the offspring might have blue eyes or brown eyes. If the gene for blue eyes is more dominant then the offspring is more likely to have blue eyes. The phenotypic effects of genes whose alleles behave in an epistatic way is context dependent, meaning that the effect of an allele might change depending on alleles present at other loci. LESSON 9 Question 1: species are constantly evolving, sometimes resulting continuous distribution of population differentiation. It is very hard to name species as they are always changing from time to time. Each species diversifies and branches to small sub species. This species is not different from each other as they share the same genotype. If two lineages were to diverge what differentiating factors would be used to name both as different species. species are often defined in relation to research methods. Bacteriologists can’t use the BSC as bacterial groups exchange genes constantly but at a low level. They thus tend to use genetic clustering algorithms to define somewhat stable evolving units. Paleontologist can’t use the BSC because they can’t test if two fossil species can mate. They’d look for morphological clusters. A professor of mine once said: “Pick the species concept that works for your group and stick with it.” Both will use the method of which they used to research for the organisms to name the species. This is beneficial as it will help them remain with one class of species which will aid in their research. Question 2: A-2; B-4; C-1; D-5; E-3. Premating, ecological isolation is a form of reproduction barrier that reduces chances of interspecific mating. This is when individuals of the same species do not mate with each other hence has helped in completing speciation. A good example is when two species of gymnosperm tree release pollen at different times. It is a mechanism that they have developed to prevent the trees from mating and producing hybrids. This is a way of preventing diversification in a species. Postzygotic, intrinsic sterility is a mechanism that blocks reproduction after fertilization and zygote formation. It mainly occurs when members of the same species mate and produce a zygote. The hybrids are not productive hence the mating is often considered unsuccessful. A good example is when a horse and a donkey mate to produce hybrid offspring. The hybrid offspring cannot reproduce themselves. Premating, behavioral isolation is when individuals in a species make decision on who they are going to mate with. All organisms have their own way of expressing their urge to mate. The males have their own way of luring or calling the females to mate. A good example is how the mating dances of male birds of paradise differ between species such that females cannot recognize interspecific males. If behaviors have diverged between species, they might not recognize each other as possible mates. Postzygotic, extrinsic, ecological in viability is when the offspring of reproduction are either infertile, weak, or very weak to survive. An example is the hybrid Darwin’s finch that have reduced survival and reproduction because their beaks are misshaped for the seed resources. It will be hard for the birds to survive as their beaks are not well adapted to feeding hence, they will be selected against by natural selection. Question 3: 1-A, 2-C; 3-D; 4-B; 5-E. Coyne and Orr (1997) compiled data on reproductive isolation between species of Drosophila fruit flies. They were investigating the possibility of prezygotic isolation and postzygotic isolation, which would evolve fast among the fruit flies. Open circles are a comparison between species that live in a different place. They belong to the same ancestry which have evolved into different species due to geographical separation. The open circles are used to present the comparison between the allopatric species while the dark triangles are used to compare the sympatric species pair. Sympatric species are populations of the same ancestry that evolve into different species without any geographical separation. The Y-axis panel A is a measure of the frequency of mattings during free choice trials. It was a measure of how willing individuals were to mate with other individuals of the same or different species. It was done by putting individuals in an enclosed space and measuring how often individuals were mating. It was mainly used to measure prezygotic isolation between individuals. It was used to investigate how the behaviors of the individuals would be a barrier to mating. while the X-axis Panel B is a measure of the viability of offspring from forced laboratory crosses. It was done by artificial insemination where females were inseminated with sperms of males of the same species and those of different species. It was used to measure the viability and survival of the hybrid offspring against the other offspring. I was a way of measuring postzygotic isolation. Question 4: Prezygotic isolation evolves faster than postzygotic but only in sympatry. For the allopatric species both postzygotic and prezygotic isolation evolve steadily. If you were to draw a line through all the circles, you would notice that the line is straight showing that postzygotic and prezygotic isolation evolve steadily. However, this is not the case for the sympatric group of species. Prezygotic isolation evolves faster, most occurring immediately after divergence. This implies that natural selection must favor the evolution of prezygotic mechanisms when two species are interacting because only when species were in contact did prezygotic mechanisms evolve. The sympatric species have been in the same geographic area; hence this may cause them to develop a mechanism to prevent matin between them. This is to ensure that gene flow in the species is maintained. Question 5: In a situation where there is a homogenous species. They might end up being separated by geographical features such as a river, mountains or even lakes. This brings a bout allotropy in a species. In the event that the two species were to meet, then there would be mating between the two different species. This cause slight evolution of prezygotic or postzygotic isolation due to allotropy. Mating with individuals of the different species may be caused by the fact that some individuals do not recognize the different mating dances or the time for mating is slightly off. The individuals who will mate will end up producing hybrids who are weak. Th hybrids have a low chance of survival and reproduction hence at a high risk of becoming extinct. Mos hybrids are weak and cannot survive in the environments hence are selected against by natural selection. The unfit are removed leaving the individuals that are fit to reproduce. Prezygotic isolation is more rampant in sympatric individuals. This are individuals of the same ancestry who are from the same geographical area. Prezygotic isolation in sympatric individuals is advantageous as it will prevent them from mating with individuals from the other species. This will ensure that they reproduce within their own species which allows gene flow and the offspring produced are string. This make the sympatric individuals to be selected for as they are most fit to survive and reproduce. Unlike the hybrids who are weak and are unable to reproduce themselves. Question 6: UY will only be slightly differentiated from the population to its east. Slightly more differentiated from XN. Slightly more differentiated from LN. Slightly more from KL, and so on. Until it’s different enough from TL that they no longer mate. Isolation by distance builds up gradually, as selection in each location causes differentiation more than migration/gene flow can cause homogenization. As the geographical distance increases, so does the difference in interest and mating cultures. This will cause isolation due to behavioral factors as the birds may choose not to mate with the other species. This doesn’t imply that the birds are not of the same species. There are many instances when individuals from the same species did no t mate not because they are geologically different but because of the geographical difference between them.