Unit 3 Test Review PDF

Unit 3 Test Review Mutations ​ RANDOM ​ A change that occurs in DNA of an individual will randomly introduce new alleles into a population ​ This will change allele frequencies and could potentially change the entire gene pool if mutation becomes prevalent ​ The more genet...

Unit 3 Test Review Mutations ​ RANDOM ​ A change that occurs in DNA of an individual will randomly introduce new alleles into a population ​ This will change allele frequencies and could potentially change the entire gene pool if mutation becomes prevalent ​ The more genetic variation there is in a population, the greater the chance of a selective advantage to some individuals in a changing environment ​ Mutation Example: Effect of warfarin on rats -​ Warfarin is a rat poison that was used to control rat populations -​ Before its use, a few rats had a mutation that made them resistant to the warfarin’s effects -​ When they began using it, these rats survived and passed on the resistance, increasing the population of warfarin-resistant rats Gene Flow ​ RANDOM ​ Begins with two different interbreeding populations that have different allele frequencies ​ Animals that migrate to a neighbouring group to mate will introduce new alleles to that population which can cause a change in allele frequencies in one or both of the populations ​ ​ Through gene flow, modeled here, genetic information is exchanged between individuals of different populations Genetic Drift ​ RANDOM ​ The change in allele frequencies by chance due to random events in a small breeding population ​ The smaller the population, the less likely it is that the parent gene pool will be reflected in the next generation ​ The failure of a few individuals to reproduce intensifies the effects of genetic drift ​ Conditions required for genetic drift: small populations. This will cause changes to appear drastic. ​ Larger populations appear stable ​ With small populations only a short period of time is required to have a significant effect on the gene pool The Bottleneck Effect ​ Change in gene distribution due to a sudden decline in population ​ Sometimes events (natural disasters, invasive species, overhunting) can greatly reduce a population (often to the point of extinction)  Unit 3 Test Review ​ Since there’s only a few survivors, only a fraction of the original gene pool is present, which causes a decrease in diversity (allele frequencies change) ​ ​ Example: Colour Vision Deficiency -​ A typhoon devastated a small island part of Micronesia. -​ Only 30 survived, one of which carried a genetic mutation that causes colour vision deficiency. -​ Today, 10% of the current population have the deficiency, while in the general population the condition is very rare. The Founder Effect ​ A few individuals occupy a new area & the population will have been started by a very limited number of members of a given species (occurs frequently on islands) ​ “Founders” may carry with them a genotype that is atypical of their species and it passes on to virtually all of the population ​ Allele frequencies change (compared to parent population) ​ ​ Example: Polydactylism, when a sixth finger or toe grows, is common in Amish populations where there is a lack of genetic diversity (founded by only a few families) Non-Random Mating ​ Involves mate selection, which is NOT random, based on preferred phenotypes or when in an inbreeding situation ​ Includes inbreeding and preferred phenotypes Non-Random Mating - Preferred Phenotypes ​ Choosing a mate based on physical attributes or behavioural traits. ​ Examples: -​ courtship displays (greater sage grouse strut display) -​ male-male competition (male caribou spar using their antlers), those that are successful more likely to reproduce Non-Random Mating - Inbreeding ​ When mating pairs are limited an organism is more likely to breed with an organism genetically  Unit 3 Test Review similar to themselves. ex. self-fertilization in flowers ​ This doesn’t affect distribution of alleles directly but it causes more homozygous genotypes which may cause more harmful alleles to be expressed, causing disease ​ Inbreeding individuals have higher rates of producing offspring with more deformities, health issues and genetic diseases Natural Selection and its Types ​ Genetic information leads to the expression of a specific physical trait that provides selective advantage ​ Over time that physical trait will increase in frequency, causing a change in allele frequencies which can lead to evolutionary change ​ Several types 1.​ Stabilizing Selection 2.​ Directional Selection 3.​ Disruptive Selection 4.​ Sexual Selection Stabilizing Selection ​ Selective pressure that favours intermediate phenotypes and selects against extremes ​ Distribution narrows ​ The population before natural selection (top) and after (bottom). The brown area shows the general population. ​ Example: Human Birth ​ Directional Selection ​ Selective pressure favours phenotypes that occupy ONE extreme but not another ​ Distribution shifts (peak shift) Disruptive Selection ​ Extremes of phenotypes are selected for while intermediate phenotypes are selected against ​ Twin peak distribution  Unit 3 Test Review ​ Sexual Selection ​ Selection of a trait that increases the mating success of the individual ​ Often involves competition between males through combat or through visual displays ​ Such selection can lead to sexual dimorphisms (striking differences in the physical appearance of males and females) ​ Also involves the choice females make for mates ​ ex. physical traits like colour, song, strength... What is Speciation? ​ Also called macroevolution ​ The formation of new species from existing species. ​ Two populations become reproductively isolated over time (i.e. become two different species). -​ Some members of a population change so much that they are no longer able to reproduce viable, fertile offspring with members of the original population. ​ With little or no gene flow between them, the populations become reproductively isolated from each other Reproductive Isolation Mechanisms ​ Keeping species distinct ​ Include geographical barriers and biological barriers to reproduction Pre-Zygotic Isolating Mechanisms (5) ​ mechanisms will not allow a zygote to form since they can -​ prevent mating between different species -​ prevent the eggs from being fertilized if different species attempt to mate. 1.​ Behavioural Isolation ​ Any special signals or behaviours that are species-specific will prevent interbreeding with closely related species. ​ Ex. bird songs differ for a specific species, courtship rituals of elk, pheromones (chemical signals) of insects 2.​ Temporal Isolation ​ Two species may occupy the same habitat but have timing barriers. ​ Ex. Different reproductive cycles for flowering of plants or animal mating occur at different  Unit 3 Test Review times. 3.​ Habitat Isolation ​ Two species may live in the same general region but in different habitats, so they may rarely encounter each other ​ Ex. Ground squirrel species woodchucks live in fields at lower elevations while marmots live in alpine meadows in high elevations 4.​ Mechanical Isolation ​ Two closely related species may attempt to mate but are unsuccessful because their anatomy is incompatible ​ Ex: structural differences in reproductive organs → Insects - genitalia have very specific shapes that act as a lock and key. Even something that looks similar will not work 5.​ Gametic Isolation ​ Gametes from two different species may meet but do not fuse to form a zygote ​ Ex. Sperm of male may not survive female reproductive tract ​ Ex. Giant clams release sperm & eggs into water and they will recognize each other by molecular markers Post-Zygotic Isolating Mechanisms (3) ​ In a few cases, animals of different species can overcome pre-zygotic barriers and will produce a hybrid offspring ​ 3 types of post-zygotic isolating mechanisms prevent hybrids from developing into viable, fertile individuals 1.​ Hybrid Inviability ​ Zygote dies shortly after fertilization due to genetic incompatibility ​ Normal mitosis is prevented from occuring after the zygote is formed ​ Ex: a zygote will form between a sheep and a goat but it never comes to term 2.​ Hybrid Sterility ​ Two species mate and produce hybrid offspring but it is sterile and thus cannot reproduce ​ Meiosis fails to produce normal gametes in the hybrid because the chromosome number or structure of the parent species differ ​ Ex. Sterile mules result from mating female horse with a male donkey 3.​ Hybrid Breakdown ​ The first generation of living hybrids CAN undergo meiosis properly to produce normal gametes but THEIR offspring cannot ​ The second generation offspring will die. They are too weak to live long or they are sterile  Unit 3 Test Review What is Speciation? ​ The evolutionary process by which a new species arises ​ Once an isolating mechanism has prevented gene flow, populations must remain genetically isolated from each other for speciation to occur Modes of Speciation 1.​ Sympatric Speciation ​ Occurs when populations that live in the same habitat diverge genetically and become reproductively isolated. ​ More common in plants than animals ​ Chromosomal changes in plants or non-random mating in animals alters gene flow ​ The result is reproductive incompatibility without geographical isolation 2.​Allopatric Speciation ​ More common ​ Occurs when populations are separated by a geographical barrier and diverge genetically. ​ A type of speciation whereby two or more groups within a population are geographically isolated ​ Over time, the lack of gene flow and accumulation of mutations leads to genetically distinct populations ​ The original populations can no longer interbreed Divergent Evolution ​ Pattern of evolution where two species become distinct as they change in response to environmental conditions ​ Share many homologous structures ​ Ex. limbs of vertebrates ​ Forelimb of 4 different mammals. They are similar structures, which were present in the common ancestor. They persist in the diverged organisms although they have different functions Convergent Evolution ​ Pattern of evolution where similar traits arise in two species independently in response to similar conditions, not because they share a common ancestor ​ Share many analogous structures ​ Ex. Wings in bats, birds and bugs → Bones arranged differently but independently achieve the same function, flying ​ Different internal bone structures of wings in  Unit 3 Test Review 1.​ Reptiles 2.​ Mammalian bats 3.​ Birds Speed of Evolutionary Change ​ Gradualism: change occurs slow and steady (big changes occur by accumulation of many small changes). ​ Punctuated Equilibrium: long periods of stasis (nothing happening, equilibrium) interrupted by bursts of divergence (big changes). ​ BOTH MODELS ARE AT WORK ​