Evolution Exam Review 1 Define evolution and make sure you understand the definitions of the terms we used in that definition Evolution The process of descent with modification Change in gene frequencies over time Descent with modification The evolutionary process by which species change over time 2 What was Darwin s critical insight into the mode of operation of this natural selection idea In other words how did his conception of selection differ from the ideas about selection that were circulating in scientific circles before he proposed his idea Original World Views Differences in species were transient and irrelevant There was an essential species They did not change or have organic mutability Charles Lyell Change and shape of the earth environment Principles of Geology Extinctions varied with climate change species unfit to handle environment Presence for the Prolific Struggle for Existence highlighted the ideas of selection before Darwin s time Darwin Natural Selection The association between trait variation and fitness of offspring left behind With Darwin VARIATION became the key driver for selection 3 What do we mean when we speak of hidden genetic variation in the context of selection and evolution Genotypic variation that is hidden and displayed as similar phenotypes EX Gametic Disequilibrium caused through linkage Less individuals than possible genotypes allows for Gametic Disequilibrium to mask phenotypic variation Ad Mixture Results the same as linkage and G D Selection acts on phenotypic variation without any visible variation we cannot illustrate evolution With recombination evolution rates can increase without knowledge 4 How do entirely new genes appear to arise Think about this carefully you have to be clear about what we mean by a new gene a gene whose product has a different function than the function performed by its ancestor and what steps unfold to make a gene new Not Mutation Origin of new genes 1 Unequal Recom And gene duplication 2 Domain Shuffling mix and match domains on different genes creates homology among a Creates TRANSPOSABLE ELEMENTS can build a mutant gene through transposable 3 Alternative Splicing synonymous mutation splices a gene causes mutation not seen in protein coding however continues and becomes a DELETERIOUS GENE domains elements 4 Overlapping genes 5 What was the significance of Darwin s observing the differences among populations of many species or closely related species e g mockingbirds tortoises etc on different islands in the Galapagos in their morphological features Darwin was fascinated to see that each island had some of the same species but these species were unique to each island Galapagos was a collection of islands in the same area Darwin also noted that each variation of species was well suited for their environment 6 A critical observation about the fossil record even in the mid 19th Century was that the number of recognizable species in certain groups seemed to increase from the deeper layers on upward What is the significance of this observation With the idea of Stratigraphy fossil organized in respect with layers through time acting as markers like coal deposits animals that were closer to the surface were more recognizable and common with current life but the as the fossils were deeper we gained knowledge of the kind of species that existed during that time which were less common with the existing species Mammals close to the surface insects further down and uncommon marine animals the furthest down This also suggested climate change and species evolution 7 What did Darwin s critics mean when they criticized his concept of natural selection as one that was not likely to result in stable change When looking at chicken eggs chickens who were selected to make more eggs plateaued This questioned the stability and ability of traits to be selected and for evolution of these traits 8 Darwin s notion that selection worked on small differences among individuals was subjected to several strong criticisms What were these criticisms One of the criticisms was that there was a threshold for certain characteristics i e guppy size amount of eggs a chicken can lay that could not be broken after being selected for This was a time before genetics so there was also a notion of Blending Inheritance that these small variances were meaningless and unimportant 9 Another critical observation about the fossil record is its order from deeper to shallower layers that for example the first appearance of fossil mammals in an area is never below the first appearance of fish if there are fish or fossil amphibians or reptiles This is just one of many for example cases we could list many others at even finer levels of detail e g just within insects you could substitute two winged flies for mammals and dragonflies for fish What would Darwin offer as a hypothesis to explain these observations What alternative hypotheses can you describe Darwin s theory would be that the species that appeared later were descendants of the ones seen earlier In contrast Lyell believed that these newer species were a result of special creation 10 Why was Castle s selection experiments on hooded rats considered so decisive in supporting Darwin s idea of how natural selection would work Discovery of recombination change color distribution how to illustrate Gametic Disequilibrium Meaning there was no mutation just hidden phenotypic variation 11 What do we mean by hidden genetic variation and why was its discovery so significant for Darwin s hypothesis about natural selection More genotypic variation than you can see in the phenotypes Nonrandom assortment self fert Etc hides genetic variation Genotypic variance released by recombination and outcrossing via sexual reproduction causes gametic disequilibrium Coinheritance of alleles different loci Drosophila Bristle is an example of environmental influence on genetic variation 12 Mutation rates are sufficiently low per locus per gamete per generation that this is not a strong force in producing evolution Yet a close personal friend of yours claims that in fact mutants and therefore mutations are very common in natural populations and therefore mutation rates play a significant role in evolution Resolve this paradox Mutation rates may seem like a big player in evolution as genetic variance increases from the generational mutations However there is a certain proportion of lethal mutants that account for deleterious mutations