organic evolution exam 2 Questions & Amswers

For allele frequencies to change there has to be: - ANSWERSvariation (there have to be different alleles) Variation in a population comes from : - ANSWERSMutation Gene Flow Once genetic variation has been established, what causes the allele frequencies in a population over generations? - ANSWERSNatural selection Genetic drift More Gene Flow Only natural selection causes : - ANSWERSadaptive evolution Evolution by natural selection involves both ___ and _____ - ANSWERSchance and "sorting" New genetic variations arise by chance Beneficial alleles are "sorted" and favored by natural selection Natural Selection acts on the _______ not the _______ - ANSWERSPhenotype, Genotype phenotypic diversity is affected by : - ANSWERS1. Multiple Genes (=Quantitative traits) 2. Interactions between different genes 3. Trade-offs example of multiple genes: - ANSWERSwheat color: Three separate genes (A, B and C) Independently assorting i.e., on separate chromosomes Alleles show incomplete dominance (heterozygote is intermediate between the homozygotes) Dominate alleles contribute additively to pigmentation because of independent assortment and the additive effect of the dominant alleles, some colors are more common than others Quantitative Trait - ANSWERSWhen many genes, each behaving individually, contribute to a phenotypic feature in a cumulative way, the feature is called a Quantitative Trait More genes involved in the trait, the more ______ exists - ANSWERSvariation Patterns of Natural Selection in Quantitative Characters - ANSWERSDirectional Stabilizing Disruptive (=diversifying) In any species and at any point in time, all three types of selection may be acting. Directional Selection - ANSWERSPhenotypes at one extreme die off or fail to reproduce and those at the other extreme leave a higher number of offspring. This shifts the average frequency distribution towards the favored extreme. ex.Biston betularia- moths White phenotype Dark phenotype Originally, the vast majority of peppered moths had light coloration. Widespread pollution - esp. soot - covered the trees and the white moths became more obvious to predators. Dark-colored moths flourished because of their ability to hide on the darkened trees. They left more offspring Stabilizing Selection - ANSWERSIndividuals with extreme phenotypes die or fail to reproduce resulting in populations of individuals with intermediate phenotypes. Most common in stable, unchanging environments where selection has remained the same for years. disruptive selection - ANSWERSextreme phenotypes become more frequent from generation to generation because they survive to reproduce while individuals with intermediate phenotypes die or fail to reproduce.Diversifying selection results in polymorphism (two or more different forms are common). ex.)taurus scarab beetles-one shows head spines the other does not Males with elaborate horns or antlers may attract more mates but die younger because they are costly to grow, make the animal clumsy and more obvious to predators. Males without elaborate horns or antlers attract fewer mates but live longer. Example of Tracking Natural Selection Affecting Quantitative Traits - ANSWERSUse survivorship or number of offspring as an approximate measure ex) beak of finch- Step 1: Capture weigh, measure, and identify hundreds of the birds and record their diets of seeds Step 2: For the seeds the finches eat, measure seed size and seed hardness Step 3: Identify and count the seeds present on a representative plot Step 4: Correlate the information with climate data (wet or dry) Conclusions Bill size changes incrementally as the environment changes Quantitative traits allow organisms to respond more precisely to environmental change Epistasis - ANSWERSgenes can mask each other's presence or combine to produce an entirely new trait. The genes involved in a specific epistatic interaction may still show independent assortment at the _______level but the ______ ratios may appear to deviate from those expected with independent assortment. - ANSWERSgenotypic, phenotypic The Law of Independent Assortment - ANSWERSOriginated by Gregor Mendel When two or more characteristics are inherited, individual alleles assort independently during gamete production, Gives different traits an equal opportunity of occurring together. Regulatory genes may affect more than one feature Example heat shock gene Hsp90 (encodes a heat shock protein which helps organisms cope with stress) - ANSWERS trade off: - ANSWERSChanging one feature for the better might change another for the worse. Pleiotropy: - ANSWERSOne gene Can affect multiple traits E.g. White cats with blue eyes are usually deaf A single gene controls pigmentation pigmentation plays a role in maintaining fluid in ear canals Antagonistic Pleiotropy: - ANSWERSSelection may act positively for one trait and negatively for another in humans, the p53 gene directs damaged cells to stop reproducing, thereby resulting in cell death. This gene helps avert cancer by preventing cells with DNA damage from dividing, but it also suppresses the division of stem cells, which allow the body to renew and replace deteriorating tissues during aging. This situation is therefore an example of antagonistic pleiotropy, in which the expression of a single gene causes competing effects, some of which are beneficial and some of which are detrimental to the fitness of an organism. Cline - ANSWERSThe pattern of genotypes and phenotypes over a geographical range. -Step Cline - ANSWERS- each geographical subarea has its own unique adaptations and dominate phenotypes. the rat snake, differs markedly in color and pattern over its range. -Smooth Cline - ANSWERS- the variable phenotypes are not distinct from each other so that over the geographic range the adaptations blend into each other. Wild lion populations have genetic differences that result in different manes and that vary gradually with local climate differences. Combination of Environment and Quantitative Traits - ANSWERSBy absorbing ultraviolet (UV) radiation from the sun, melanin controls the amount that penetrates the skin. UV radiation is needed to make vitamin D, but excess UV can damage health and destroy vitamin B (folate). It is surprisingly difficult to define a "species" in a way that applies to all naturally occurring organisms, and the debate among biologists about how to define "species" and how to identify actual species is called the - ANSWERSspecies problem. Biological Species Concept - ANSWERSA species is a group of actually or potentially interbreeding natural populations which are unable to successfully mate or reproduce with other such groups. Biological Species Concept: criticisms - ANSWERS-Not useful for asexual organisms -How can you recognize interbreeding ability? It is not always possible to observe! Especially in fossil organisms! How much interbreeding is needed? Hybrids - ANSWERSare the offspring of crosses between different species hybrid zone - ANSWERSa region in which members of different species mate and produce hybrids. Hybrid zones are caused by - ANSWERSmigration, habitat disturbance, invasive species, etc. Widespread Range - Ring Species - ANSWERSSometimes the extreme ranges of the species will loop back and overlap with each other. In the zone of overlap there may be no mating and significant morphological differentiation. This special type of geographic variability is often called a ring species What Do Scientists Want In a Concept? - ANSWERSUniversality: It must be possible to apply the species definition to as many different types of organisms as possible. Applicability: It should be applicable in all circumstances. E.g., Physicists would be upset if their concept of "element" applied only to metals. Theoretically Significant: It must describe a real event and further our understanding of that event. Biological species concept - ANSWERSnot universality, not applicability, just theoretically significant Morphological Species Concept - ANSWERSA species is a set of individuals with morphological features in common Individuals of a species are similar to one another, yet morphologically distinct from individuals from other species