Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Ch. 17 Part 4 • • • • Darwin-Wallace Theory of Evolution 1856 Charles Darwin and Alfred Wallace Natural Selection believed to be mechanism by which evolution occurred No knowledge of genetics, alleles, or inheritance Theory based on observations and deductions Observation Organisms produce more offspring than are needed to replace parents • Deduction • There is competition for survival “struggle” for existence Natural Populations tend to remain stable in size over long periods of time There is variation among the individuals of a given species • Best adapted variants will be selected for by natural conditions operating at the time (natural selection) • Best variants have selective advantage • “Survival of Fittest” Natural Selection can act on variation within a population to bring about changes in allele frequencies Species and Speciation • Species: • A group of organisms with similar morphological, physiological, biochemical, and behavioral features • Can interbreed to produce FERTILE offspring • Reproductively isolated from other species • Morphological features structural features • Physiological features features regarding how the body works • Biochemical features include sequences of bases in DNA molecules AND sequences of amino acids • Speciation is getting one group of species to split into new, different groups • This large group MUST become separated or ISOLATED in some way so they can NO longer interbreed… How to Determine if organisms are the same or different species…. • Species need to be tested to find out if they can interbreed successfully & produce fertile offspring • Problems: • • • • • • • Organisms dead (fossils/museum animals) Same sex Little access to facilities to test No time to test Organisms will not breed in captivity Reproduce asexually Immature (not at reproductive age) Key determination if two organisms belong to the same species or not: inability to interbreed with each other successfully….in order to for one group of organisms to produce another group of organisms that cannot interbreed successfully, the two groups must under go REPRODUCTIVE ISOLATION…. How to MAINTAIN Reproductive Isolation • Isolating Mechanisms • Review: What is a ZYGOTE??? • Pre-zygotic isolating mechanisms (before a zygote is even made) • Ways to PREVENT fertilization 1. 2. 3. 4. Behavioral isolation Mechanical isolation Gametic isolation Incompatibility of pollen and stigma in plants • Post-zygotic isolating mechanisms (after zygote is made) • Ways to prevent the formation of FERTILE offspring 5. 6. 7. Hybrid inviability Hybrid sterility Hybrid breakdown Pre-zygotic isolating mechanisms (before a zygote is even made) 1. Behavioral isolation 2. Mechanical isolation 3. Gametic isolation 4. Incompatibility of pollen and stigma with plants • Species A doesn’t recognize species B’s mating ritual • Species and mates/flowers at different time or season than species B (temporal isolation) • Reproductive parts are incompatible • Animals physically unable to mate • Male gametes do not survive in the environment of the female gamete • Female gametes do not recognize male gametes • Gametes cannot fuse with each other 5. 6. 7. Post-zygotic isolating mechanisms (after zygote is made) Hybrid inviability • Failure of cell division in zygote • Zygote fails to develop properly Non-viable offspring • Offspring dies soon after birth Hybrid sterility and breakdown • Hybrid becomes functional adult but they are reproductively sterile • Eggs or sperm are non-existent or dysfunctional • Viable but sterile offspring • Hybrids produced actually DO produce offspring but their offspring have reduced viability or fertility • Species: group of individuals capable of interbreeding and producing viable offspring • Speciation: formation of a new species 2 MAJOR processes of speciation: 1.Allopatric Speciation 2.Sympatric Speciation Allopatric speciation • speciation occurred in different regions • Key: geographical separation • Geographical isolation Sympatric speciation • one population of one species became two species while in the same geographic region with no physical separation • (temporal isolation, reproductive isolation, behavioral isolation) 1. Allopatric Speciation • Geographical Isolation • Geographic barrier prevents interbreeding between members of the population • Barrier leads to reproductive isolation • Allele frequencies change (due to natural selection, genetic drift, or mutation • If gene pool changes too much, interbreeding between populations will no longer be possible= NEW SPECIES Allopatric = different places • Selection pressures in one area very different from original area • Results in different alleles being selected for • Over time morphological, physiological, behavioral features in new area population become so different from original population • Two populations can no longer mate • new species has evolved 2. Sympatric Speciation • New species formed WITHOUT geographic barrier • Due to: • Reproductive isolation • Behavioral isolation • Temporal isolation • How Sympatric Speciation Can Occur: • Polyploidy • Polyploid organism: organism that contains MORE than 2 complete sets of chromosomes in its cells • Cause: • Meiosis gone wrong • Results: • One or more gametes end up with 2 sets of chromosomes instead of 1 • If fertilization occurs between two of these gametes: 2N + 2N = 4 N TETRAPLOID • If fertilization occurs with another normal gamete, you get 1N + 2N = 3N TRIPLOID Some Common Polyploids…. Tetraploids • When two messed up gametes fuse • instead of 1N + 1N = 2N…you get 2N + 2N = 4N • STERILE (most of the time) • Cannot produce gametes • 4 of each chromosome • All 4 try and pair up during meiosis 1 = big mess • Difficult for cell to divide and produce gametes with equal number of chromosomes • Tetraploid can grow and develop into multicellular organism that reproduces ASEXUALLY • Uses mitosis to grow and develop and reproduce • No pairing up of chromosomes required in mitosis (no tetrads) • Occurs often in plants (NOT animals b/c animals cannot reproduce asexually) Tetraploid Plants • Some manage to produce gametes • Diploid gametes • (NOT haploid 4N 2N) • If diploid gamete 2N fuses with a normal plant gamete 1N you will get an organism that is 3N (TRIPLOID) • Grows and develops normally through mitosis • Sterile cannot go through mitosis to split chromosomes evenly between daughter cells • Original tetraploid plant and diploid plant that produced this TRIPLOID offspring cannot successfully interbreed • New triploid offspring is considered a NEW SPEICIES in just one generation Types of Tetraploids: Autopolyploid vs. Allopolyploid Types of Tetraploids: Autopolyploid vs. Allopolyploid • Autopolyploid • Polyploid that contains four sets of chromosomes all from the same species • Meiosis not likely to occur b/c all 4 chromosomes try to pair up with each other • If self-fertilization occurs tetraploid Allopolyploidy • Polyploid that contains 2 sets of chromosomes from one species and 2 sets of chromosomes from another species • Meiosis can occur more easily in these plants b/c chromosomes are not identical • 2 chromosomes from one species pair up with 2 chromosomes from the other species • Meiosis can reach a successful conclusion (producing gametes that are 2N…still not N but they can lead to new triploid species) • Considered Fertile • Cannot interbreed with individuals with parent species (it is a new species) • Ex. Cord grass Spartina anglica Speciation through Allopolyploidy: Spartina anglica • Spartina anglica • Vigorous grass in salt marshes • Before 1830 • Spartina maritima • 1829 S. alterniflora imported from America • S. maritimia and S. alterniflora interbred hybrid created S. townsendii • Diploid (2N) • One set of chromosomes from S. maritimia • One set of chromsomes from S. alterniflora • B/c of different sets, they CANNOT pair up during meiosis = unsuccessful meiosis • S. townsendii CANNOT interbreed with its parent species = NEW SPECIES • Sterile BUT can reproduce ASEXUALLY • Produce rhizomes (long, underground stems that propagate new plants) 1892 MAJOR Event • S. townsendii produced cells with DOUBLE the number of chromosomes (due to faulty cell division) • Fusion of 2 abnormal gametes of S. townsendii produce TETRAPLOID plant that is an ALLOTETRAPLOID • 2 sets of chromosomes from S. maritima • 2 sets of chromosomes from S. alterniflora • Chromosomes CAN pair up during meiosis = FERTILE plant • S. anglica • More vigorous than other 3 species Comparing Amino Acids Between Species • Reveals similarities between species • Number of differences between the amino acid sequence of a particular protein between 2 different species gives a measure of how closely related the species are • Cytochrome C protein in ETC • Humans, rats, and mice • All three molecules of cytochrome c had 104 aa • Sequences of mouse and rat cytochrome c proteins were identical • 9 aa in human cytochrome c are different from mice or rat sequence • Most of substitutions in human cytochrome c are of amino acids with the same R group • substitutions change codon but still produce same amino acid • Mice and rats closely related…common ancestor • Humans distantly related, common ancestor with mice and rats is LESS recent Comparing Nucleotide Sequences of mitochondrial DNA • Human mitochondrial DNA inherited through the female line • Zygote contains mitochondrial DNA from the OVUM • Mitochondrial DNA (mtDNA) • Circular DNA • Does not undergo crossing over • Changes to sequence of nucleotides in mtDNA can only occur because of mutation • Mutates faster than nuclear DNA • mtDNA does not contain histones (which protect nuclear DNA) • Oxidative phosphorylation in mitochondria produce forms of free radicals (oxygen) that act as mutagens to mtDNA Homo Sapiens and mtDNA • Different human populations = differences in mtDNA sequences • Evidence for origin of H. sapiens in Africa and later species • All modern humans are descendants of “Mitochondrial Eve” • Woman who lived in Africa between 150 000 and 200 000 years ago • Derived from molecular clock hypothesis: • assumes constant rate of mutation over time • Assumes the greater the number of differences in the sequence of nucleotides, the longer ago the individuals shared a common ancestor • Clock is calibrated by comparing nucleotide sequences of species whose date of speciation can be estimated from fossil evidence Anole lizards and mtDNA • mtDNA analysis of anole lizards in Caribbean and adjacent mainland show ALLOPATRIC SPECIATION occurred • Each island species of lizard is found on one island or a small group of islands • Three species of Anole lizards are more closely related to A. porcatus than to each other • A. brunneus • A. smaragdinus • A. carolinensis • Suggests that species have EACH originated from separate events in which a few individuals of A. porcatus spread from Cuba to three different places Extinctions • When a species disappears from Earth forever • International Union for Conservation of Nature (IUCN) • Annual Red List threatened species world wide • 2013 21,286 species are threatened • 2015 more than 22,000 species threatened CLICK HERE • Mass Extinctions • When a huge number of species becomes extinct at one time • Many times natural asteroid colliding with Earth Human Impact on Extinction • On the bring of another mass extinction • Due to habitat destruction • Species are adapted to specific habitats with a range of environmental conditions • Human activity destroying habitats: • Climate change • Competition • Habitat Loss due to: • Draining wetlands • Deforestation (rainforests) • Pollution (air, soil, water) • Hunting (sport and/or food) High vs. Low Profile Endangered Species • High Profile Endanger Species • Mammalian species • Panda, rhinos, tigers • Tigers in China • Global population: 5000 • Human population in tiger habitats (China and India) add pressure to remaining population • Tiger products sought after by humans hunting/poaching • African Southern White Rhino • Global population: 100 • Green plants • Low Profile Endanger Species • Invertebrates • Kerry slug • Unknown threatened species • Protoctists • Prokaryotes Extinctions • Africa • Western Black Rhinos • Northern White Rhino • Extinctions due to: • Lack of political support for conservation • Increasing demand for rhino horn • Internationally organized criminal groups targeting rhinos How to Address Extinctions • Stop concentration on high-profile species • Too difficult or too costly to preserve • Focus conservation efforts on other species that will yield a greater degree of success • Plants and animals that CAN be saved • Focus on conservation of ENTIRE ecosystems rather than single species