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Introduces evolution as change in populations over generations and explains DNA, genes, alleles, and genomes as the genetic basis of heredity and variation.
this lecture is evolution part two
so evolution what is the definition of evolution um in general evolution is in the context of populations so what happens to the genetic makeup of um of organisms in a population throughout from one population to the next fromone generation to the next so the genetic makeup and the different genes frequencies or proportions if that changes from one population to the next from one generation to the next then we talk about evolution
so we can't while we won't go into details of chemistry we can't talk about the evolution without mentioning or at least highlighting the genetic material that i refer to because the definition of evolution was change in the geneticmakeup in the genetic material in the proportion of genes or alleles from one population to the next one generations so what is the unit of inheritance what is this genetic material i refer to so dna is the genetictemplate of an organism dna is um the large molecule responsible for heredity responsible for what an organism looks like how an organism behaves how it functions what are the different predispositions to illnesses so it's the genetic template sodna the nucleic acid in dna is responsible for this um heredity and dna or um the oxidable nucleic acid uh dna is the acronym for the dioxide ribonucleic acid um it's a large molecule it's uh in in biology
we refer to large molecules as macro so macro what i call and not only it's large but it's built from repeating sequences of the same type of building blocks or nucleic nucleotides excuse me and um it's also anorganic molecule so organic molecules are what build up and living organisms and they also are composed of uh carbon uh carbon atoms so an organic and molecule to be organic it has to have carbon in it and inaddition an other carbon or a hydrogen atom that the carbon um importance to but again in the chemistry details are not that important at this point the importance is that it's a large molecule it's an organic molecule andit's the molecule that's responsible for heredity of organisms um as you can see here we also refer to dna as a double helix because we see two large chains of the dna that align to each other spiraling as
a spiral staircase forming the characteristic um shape of this molecule which is the double helix so again the genetic code to make an organism
the organism unique is contained in the dnaso similarities and differences among organisms are due to their genetic material so if you break down the dna so we have here the double helix and it has sequences of nucleotides and specific sequence at the specific location denotesa gene so at the specific location and length of the dna molecule one of the strands um and then doubled up here so we have the gene which is the succulents responsible it's the unit of finality it's responsiblefor coding a protein a protein which is an other organic macromolecule of living organisms so there are many many genes um so lining up so each sequence that calls for a protein is a gene and the next sequencethat quotes for the protein is a different gene and a gene is responsible for coding for the protein um for the specific trait so for example eye color um that's a trait and then there are different variations of
forms of genes because um if we say a gene is responsible to code for a specific trait for example eye color but one variant of that gene could be brown eye and a slightly different one could be codingfor blue eyes or green eyes so there are different variants of a gene at a specific location for a specific trait um and those are these different forms of the gene are called alleles so we could talk abouta brown eye allele a blue eye allele a green eye allele if you think about one cell of an organism and all the dna all the genetic material in that cell is the genome and the genome is uniqueto an organism by every single cell of the organism is has the same genome talking about multicellular organisms of course there are only cellular or single cellular organisms which have just one sound like a bacteria but multicellular organisms
like humans or plants or animals or um they and they have many many billions of cells and we are saying in one organism every cell has the same genome unique to that organism
Defines populations and gene pools, then explains how evolution happens through natural selection, genetic drift, gene flow, and mutation. The section also distinguishes phenotype from genotype and shows how the environment influences traits.
so population we defined with the population was we said a group of organisms of the same species interacting with each other at the same place and time and um so but then we have all kind of populations withdifferent sizes are populations lower in the trophic pyramid um when we saw that there's more mass or more energy at the low at the producer level for example so a population of trees if you think of one speciesof course let's say maple trees and there would be more than uh fish or on the top of the food chain um predator so a population of wolves would constitute of a smaller population size or less individuals umso a population can be larger or smaller again if you think of predators organisms on the top of the food chain um their population size is less so they are smaller and producers are more um and when we
think about all the genetic makeup of all um the individuals in a population so all the genomes and because each individual has its genome if you add it all up in the population that is called the gene pooland the gene pool is important because if uh we further specify um the definition of evolution the genetic change throughout time from one generation to to the next from one population to the next and so if you notewhen we talk about the evolution we refer to what happens to populations what happens to the genetic makeup of a population over time so the genetic makeup of a population now we know it's called gene pool so wecould redefine uh evolution the definition of evolution as change in the genetic uh in a gene pool from generation to generation so if you look at this image from before the original population we see that there are some
darker beetles and there are lighter ones and in in between ten color ones and then the next generation the offspring population they can see for example the dark uh alleles the dark beetles are missing the genes or aliensresponsible for the dark color that are heritable they are not passed on to the next generation and then if we go to several generations into the future we can see that uh thanks to natural selection here um toavoid predation the gene pool has changed toward ten colored ambitions that blend in with the attend color background so this is what we we are saying that there is variation in the population uh in the external stress itselects natural selection occurs to this variation and the predator selects out those individuals that are visible in this case and the genetic makeup responsible on the genes responsible for the coloration of these beetles is heritable so it's passed
on to future generations and so these genes um alleles we can see that code for the color throughout the change in the color we can also understand that the genetic material responsible for the colors changes because we cansee the color is different in the future generation than it was in the original generation and it's because genes or alleles code for discoloration there must be a change in the genetic makeup of the organisms throughout populations generationsso evolution has occurred we can see it visually here so that was genes and genetics and and the definition of evolution now what is phenotype phenotype is the expression of the genes the genotype of organisms so the whatthe organism actually appears to be for example the different colors and shapes of the sea urchins we can see the the variation um in this population in the looks of these in this case the morphology is the physical
characteristics how the organisms look like differs so this these are phenotypes of the sea urchins um so the change the physical expression of genotype is phenotype and natural selection acts on this phenotype because we saw in the previousum slide what the bird was selecting on it was the colors of the beetles because the ones the bird could see selected out so natural selection was acting on the phenotype the physical appearance of those organizations so naturalselection is relevant to phenotype of individuals now phenotype therefore is the physical expression or morphology of organisms um which genes code for but also phenotype is behavior so how the organism acts um that's coded by the genes alsoor what is the physiology of an organism how an organism can react to its environment um whether an organism a plant is drought tolerant for example that's the physiology of the organism that's a phenotype as well or medical
traits what kind of illnesses somebody has or what kind of skills innate skills somebody has those are all manifestation of the genotype which is called this manifestation coded by the genes what appears of the organism that is thephenotype so the phenotype is coded by the genes so the genetic there is an underlying genetic constitution to make this um serotonin look the way it does or or have a plan resist a drought or have our bloodtypes be what it is or our innate abilities there is a genetic dna a code for that but also there are phenotypes with variant degrees of environmental influence perhaps easy to think about if there are identical twins whoin with humans who have the exact same genotype but one thing is uh spending a lot of time in the tropics and the other one spends more time in the tundra up in the north pole area then the
environment is very different the um twin that is exposed to a lot of sunlight you have a darker skin color the twin that is always in the cold without too much sunlight is lighter they have the same geneticmaterial but what they appear to be the phenotype is influenced by the environment as well so we have defined evolution we have established the the genetic material responsible for evolution and now let's talk about the different mechanisms ofevolution so we have talked about natural selection natural selection however is one of the mechanisms of evolution it's one example but there are many others several others and um they can interplay so one population can be influenced bynatural selection and genetic drift while mutation happens once in a while as well so these mechanisms can interplay um in the same population which evolutionary process is adaptive out of these five we are going to return to that
Describes assortative or non-random mating and genetic drift as non-adaptive mechanisms of evolution. It emphasizes how drift is strongest in small populations and can reduce variation or fix harmful alleles by chance.
so number one the non-random or assortative meeting is non-adaptive evolutionary process it happens um when it is when there is a bias in who gets to reproduce so it's it's especially important um evolutionary mechanism in populations where thereis a dominance as to who gets to reproduce so for example this elephant seals here the large meal in the middle as it's haram has the right to mate with all these females and this alpha male is protectingthem chasing over other males and while occasionally there are some sneaker meals that get to reproduce with a female but it's very rare so what it means is that while in this population there are females and there areother males and all of them genetic material constitutes to the gene pool but if only this one male gets to reproduce with the females then only these males aliens will be introduced to the next generation so the other
males who may have unique alleles um if they don't get to reproduce they don't get to pass their genes to the next um generation therefore the genetic makeup of the next generation will not have those aliens so thegenetic makeup is going to change which is the definition of evolution so this is a non um adaptive evolutionary process the non-random mating number two genetic drift is an other type of an evolutionary process it's non-adaptive as wellit's a random it's about who gets lucky so we have a population did again looking at colors coded by genetic materials so we see there is green and gray and different shades of tan and then the next generationhas uh some of these colors and and maybe with different numbers different proportions but then we see that the third generation here for example doesn't have green individuals anymore so but when we talk about genetic drift which genes
are passed on is who is lucky who is unlucky there's no pattern to it there's no a comparison well the green is advantageous or no the green is disadvantageous so we are not selecting for that this no it'scompletely random which individuals which aliens get passed on to the next generation
genetic drift occurs in all populations but it occurs strongest it's most powerful in small populations um it's a random so who is lucky who is unlucky it's a random process there's no purpose to it it's um but randomforces work stronger in small populations that's why genetic drift occurs stronger in small populations and as a result of a genetic drift um some alias can get lost um which means that a genetic variation can get reduced umin populations where genetic drift is strong so small populations we already said are prone to extinction and small populations that are at high risk of extinction and this is one of the reasons that genetic drift works stronger insmall populations adding to genetic loss adding to uh losing variation in in simple and because what allele or what genes person is lucky or unlucky it could be by random chance that unfavorable aliens um get fixed or they
become the only fixed means hundred percent that's the only alias so that would mean that all uh these beetles are gray for example if that was the only alien possible that can happen uh with high frequency due togenetic drift and it can happen that the only one that gets fixed is actually a deleterious or unfavorable alien because it's a random process
Explains gene flow as movement between populations and mutation as the source of new alleles. The lecture then contrasts these with natural selection, which is adaptive and consistently favors traits suited to the local environment.
number three number third the third mechanism of um evolution gene flow it's also non-adaptive gene flow is associated with movement so if we talk about one population this is a group of organisms of the same species interacting andthere is an other one um and once in a while occasionally we see that one individual disperses from one population to the other now if this individual has a different gene a form um so-called allele in this casea brown color it gets introduced to to the destination population and if this organism reproduces that color gets passed on to the future generation so you can see that the gene pool is changed um because of this ummovement so this is one form of evolution again because as long as we see change in the genetic makeup from population to population then we talk about evolution
so due to gym flow populations can become similar so over time and more and more individuals could be brown and there could be a movement of green back to the population so we could see them kind of becomingsimilar number four mutation is the ultimate source of genetic variation it's also a mechanism of evolution it's also a non-adaptive evolution and it's the ultimate source mutation is the ultimate process how brand new alleles or variants of genesget created or introduced in their population so for example if all of a sudden and due to mutation we could have a purple eye gene for humans and that's something that has not existed before and it could occurdue to mutation mutations result from when the cells divide and replicate there can be errors and there can be exposure to chemicals to radiation um those are some of the most common reasons for mutations mutations occur randomly they
occur rarely um and most of the time the mutations that come about are deleterious but once in a while advantageous alleles also get created due to mutation and we are arriving to natural selection which is also an evolutionaryprocess and to answer our previous question natural selection is an adaptive evolutionary process because there is a consistency there is a direction a consistency based on environmental stress based on the local environment consistently due to natural selection thefavorable uh genes get selected and the ones which are not favorable are selected again so this is adaptive adapting to the local environment uh consistently so adaptive evolution is natural selection so natural selection is not random the thegenes and alias or traits that get selected are based on the environment so it's not random that the adaptation of the nami beetle to have this exquisite combination of adaptations to collect water evolved and that those traits got
selected throughout um generation no it's adaptive to given that environment given the environment consistently those um traits were favored that is adaptive evolution and the disadvantageous alias and um genes get selected against uh consistently given the environment ofthe organism so remember child darwin is not based on referring to this idea it once struck me that under these circumstances favorable variations tend to be preserved and unfavorable wants to be destroyed are different types of natural selections
Uses beetle examples to explain directional, stabilizing, and disruptive selection. It also stresses that natural selection acts on individuals but changes gene pools over time.
so if we go back to our beetle example here visual variation and for natural selection darwin's rule number one was that variation has to exist in a population for natural selection to occur so we have light color darkcolor and most in this distribution we can see this phenotype distribution most of the individuals are tan colored so this is the different coloration along the x-axis and we can see the frequency the number of individuals most ofthem are tanned um so this orange is the original population and then this shape this distribution can change um if the the genetic material is changing therefore the phenome that changes evolves that's the blue so then we talkabout let's talk about directional selection first so um if for example the tree became and there's an example for this that when there is a lot of pollution and factories amid soot and that darkens the trees for example
then all of a sudden the dark color one of these extremes of the phenotype would be more advantageous because dark tree dark beetle that it gets the camouflage blend into the background the burst on sea so there couldbe a shift you can see a shift from the original orange and to the right which is the new uh phenotypic distribution and denoted by the blue to over the extreme toward the dark color or it could bethat the trees become lighter and then the advantage straight is the other extreme so the shift could be to the other extreme to over the light color okay so when there is a shift to one extreme or tothe other to the dark or to the light or to the bigger to the smaller is the shift in one way that is called direction or selection when the evolution tends to select against the extremes where selection is
more for the intermediateso what was happening in our example over the um tanned colors so less and less dark beetles are around lesser less and less light beetles and the ones that survive are concentrated in the middle part of this phenotypicdistribution almost all of them are tan colored that is called the stabilizing or balancing selection and then the third form which is the least common is the so-called disruptive in this case we see this binomial distribution we seethat and the selection was favoring the extremes so we have a lot of light beetles a lot a lot of dark ones and not many times so the selection is squishing toward these extremes that's the disruptive selection
so natural selection rule one is that variation is required why because um natural selection in order to be able to match the individuals to the environment it needs to have a material to select one select from and thisthis process may not be perfect because it's based on what is available if if there's no availability if all the beetles were dark then the bird would eat all of them and the population would go extinct and therehas to be favorable variation given the environment for natural selection to act on these phenotypes so having very and this is why it's incredibly important to have variation in the genetic material in a population and we keep returningto the disease if there is a disease um for example the potato blight in ireland um where there was just one variety of the potato that millions of people were relying on and there was one disease that attacked
these potatoes all of them had the same genes all of them spoiled and many many a million people get affected and several million people get affected so if there were if there was a variation in the gene pooland some individuals had a resistant gene then they would have survived so variation is extremely important because natural selection is an editing process it's not a creating process editing meaning or what is available that's what we added butnatural selection won't create the perfect gene or allele it can't it selects from what's available so natural selection happens to individuals the phenol types of individuals the bird was selecting based on what each individual looked like the phenotypeof each individual as opposed to evolution occurs to gene pools it occurs to what happens from one population is doing pool to the next generation's uh gene pool so there is a difference between them also remember natural selection
is just one type of evolution the other adaptive type but it's only one type we talked about different additional types of evolution for example mutation genetic drifting for a non-random
Shifts to macroevolution by defining species and explaining how speciation occurs through reproductive isolation. It also covers adaptive radiation, where one lineage rapidly diversifies into many species across different niches.
mutation up to now i talked about genetics um around evolution micro evolution because we talked about what was happening to the genetic material the genes under the microscopes from um generation to generation but there is also a macroevolution there are also macro evolutionary processes these are large long-term processes large-scale um processes such as speciation adaptive radiation which is an extreme kind of speciation and mass extinctionso speciation and adaptive radiation and related concepts and large-scale macroevolutionary processes um and there are processes where from one species and one species splits into two or more species um and what is the species returning to the speciesbiological species concept by ernest meyer it's a group of actually or potentially interbreeding organisms capable of producing fertile offspring so the ability to reproduce and create fertile offspring is key to the biological species concept so when we talk
about speciation we talk about um a species splitting into several species so the ancestral finch species here on the different islands of um darwin's islands the galapagos are islands a new species evolved with different features based on theirgiven environment on each island what food source was mainly available and over time they became species each of them different species because they are no longer able to reproduce um to create fertile or spring so now we talkabout different species that's speciation now the more extreme version of speciation is we talk about adaptive radiation when relatively in a short period of time a large number of species evolve so he here we see a whole bunchof finches relative to their food source so eating fruits or
feeding on mangrove trees or eating smaller seeds or larger seeds or hardest three seeds or eating cactus so based on diversity and habitat based on diversity and food sources as we introduced this whole topic talking about the beetlediversification and the diversification it was a a result of diversity and habitat and food niches of habitat and food here we can see that they can specialize into different niches and based on their based on that and morphologychanges and over time new species evolve so is speciation is a macroevolution process but it's still a result of microevolution it's still a result of what happens to the genetics the gene pool over time so here we havethe original parental um species and this ancestral or parent population is the individuals that are reproducing which with each other we have the dream pool and what happens to the genetic material we say if over time the genetic
material changes if there's evolution there is change in the genetic makeup in the gene pool over time then we can see eventually there is a differentiation in the genetic material genetic difference and we may end up with daughterspecies when we reach reproductive isolation which is at the heart of the biological species concept right reproduction is very important the key step in speciation occurs when a population accumulates so many genetic differences that they cannot produce viablefertile offspring if they meet with the parental species so there's no longer a possibility of interbreeding there's no longer possibility of producing viable offspring which was at the heart of the biological species concept so we reach reproductive isolationthat's when we talk about a brand new species being born
speciation most commonly occurs and a barrier prevents gene flow between two or more populations of a species and barriers can be geographical or ecological the populations then diverge genetically over time so we have the parental and so weare comparing noun is genetic differentiation more visually so we have the original parent of population there is often a physical geographic um division and barriers for example a river flows through and the um remember voters that noted thatdifferent pieces of um sloth monkeys were found on different banks of the amazon river so the amazon river is meandering and changing course and it could cut through a population and with time um due to mutation a newgene alien can evolve and it's starting to change this um how these populations look like begins to change and if what they look like the phenotype changes then that underline of the my genetic change so is the genetic
change that over time that this change is so much that um if the change is due to well if the color is different it may not be a problem although they are organisms that selling their mates based onsound or how they look or how they act um what it could be but the key is that the change is big enough that they cannot anymore reproduce that's when we talk about new species
Introduces mass extinction as a macroevolutionary process and reviews major extinction events in Earth’s history. It explains how catastrophic change can eliminate many species while opening ecological niches for new adaptive radiations.
so now we change course and we talk about um mass extinction which is another example of macro evolution
the extinction is nothing new on earth by most estimates more than 99 of all species that ever lived on the planet have gone extinct based on a critical analysis of the fossil record scientists agreed that there have beenfive mass extinction events when species have gone extinct at much greater rates than during intervening times um each event leading to the loss of 75 percent or or more of the species present on earth um mass extinction occurswe talk about mass extinction when relatively in a short period of time we are talking geologically so relative in a short period of time a large proportion they are talking about 75 or more percent of species um goextinct
so we have talked about five extinctions during earth is history um earth is earth's past mass extinctions were due to catastrophic events or physical changes to the atmosphere or oceans which alters the environment faster than species ability toadapt right so this is key and species can adopt they can evolve given there is genetic variation but how fast they can adapt it's also a question so if changes in the environment are large enough fast enough andspecies may not be able to adopt which is key to keep in mind when we think about climate change though most species loss um wasn't overnight taking from hundreds to millions of years to unfold these kinds of eventseventually led to the emergence of new species as surviving populations adapted to the available niches um a process that took millions of years cycles of extinction and evolution ultimately gave rise to the diversity of life you see on
earth today um estimates range to how many species we have the estimates range widely between three to 100 million species the most infamous of the mass extinction events was the kt boundary mass extinction which occurred at the transitionfrom the cretaceous to the tertiary period 65 million years ago so right about here so we if we see there were previous um extinction events for example the premium a permian extinction which was the largest extinction um previousextinction on on recorded 90 to 95 of all marine species were lost but the most famous one perhaps um that we for us is the cretaceous or the katy extinction when the dinosaurs disappeared um it was about 65million years ago most scientists agree that the skate extinction event was um set off by an asteroid impact in the gulf of mexico 76 of all living species including the dinosaurs were wiped out and um talking about mass
extinction sometimes leading to species radiation that we just talked about where um relatively short period of time a lot of new species evolved that's adaptive radiation so a adaptive radiation often occurs when there's an opportunity for a newniches of the sun and available so after all terrestrial dinosaurs went extinct at the gate extinction that um provided the opportunity for mammalian adaptive radiation there were some mammals at this time mainly small ones the biggest as bigas the cat but after the dinosaurs and extinct the terrestrial and dinosaurs meant extinct all these niches became available and then that gave rise to the mammals that gave the opportunity for mammals to radiate into these different nichesand the diversification and occurrence of many many mammal species
Discusses background extinction rates versus the accelerated extinction happening today. The lecture concludes by linking the current sixth mass extinction to human activity and the loss of habitats, resources, and genetic diversity.
throughout most of earth's history the background rate of extinction so it's important to think about the background rate background rate of extinction um and i will go to the next slide for a second and we go back andforth so in the background rate of extinction here we see is dotted line okay so throughout most of earth is history the background rate of extinction the average rate of extinction that that occurs between mass extinction events orum between the older vcn extinction which was a relatively short period of time a large amount of species and extinct and the next one the devonian extinction in between there are still a speciation and extinction occurring right butnot at accentuated rate so it's called the background rate of extinction the average rate of extinction that is low or slow the fossil record um
the total collection of fossils so the fossil record found on earth tells us that on average one or two species out of every million species who is extinct each year in a world with three million species this wouldbe three to six pieces per year if earth is home to 100 million species because the estimate of how many species we have it's between three to 100 million so if you go with a higher estimate of hundredmillion species that would be hundred two hundred species per year more scientists agree that the accelerated extinction so i accelerated rate of extinction that's when we talk about mass extinction so most scientists agree when the exile and thatthe accelerated extinction we are witnessing today so we are talking about today witnessing um today can be considered a sixth major extinction event and that is largely driven by human actions so we are saying that today we are
seeing this mass extinction the largest so compared to these five previous ones what is happening today is a higher rate of extinction the largest mass extinction where hundred two thousand times higher than the background extinction rates happening now
why as our use of resources increase driven by population growth and affluence so population growth and per capita resource use affluence our impact is becoming much more devastating for other species than previous mass extinction events we remove theresources they need to survive minimize their habit at ranges introduce new predators invasive species competition and strip them of their genetic diversity all of which slowly eliminate them okay so genetic diversity also essentialgoing back to this slide going forward here we talk about the rate of extinction is accelerating so this is a graph from 1500 it shows compared to the background humming rate of extinction so the back background extinction ratethat we talked about that is characteristic between mass extinction events you can see that since 1500 and the rate and these are all vertebrate species mammals birds fish and reptiles all of them together we can see that especially
after the 1900s this and the extinction rate is way it's it's it's it changes course becomes steep and it goes way beyond the background rate so with this with macroevolution i'm going to finish the topic of evolution andour second lecture part 1 on evolution