Gymnosperms and Angiosperms in Plant Evolution | Bio Sci 1A, Study notes of Biology

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Plant Evolution -plants were pioneers -1st green plants: 700 mya: green algae -1st land plants: evolved from green algae -one of the greatest adaptive events in the history of life Gymnosperms -naked-seed plants -gymno = naked; sperma = seed (Greek) -most are wind-pollinated -pine trees and conifers Angiosperms (flowering plants) -vessel seed plants -angio = vessel; sperma = seed (Greek) -vessel refers to carpel (includes stigma & ovary) -first appear in fossil record 125 mya -earliest were more dependent on moist habitat than later ones -evolutionary success revolves around flower -most angiosperms are animal-pollinated Plantae - Energy & Structure -root system -stem -vascular system -strength - cell walls -cuticle - waxy coating Plantae - Angiosperms -protected seeds -flowering plants -diversity in habitats -better spread: pollination, fruity seeds -coevolution Coevolution -species that mutually influence each other’s evolution -going on for more than 100 million years What animals do -birds, bees, ants, flies - visit flowers to get pollen or nectar -nectar is a saccharine secretion of plants to attract animals -result: carriers contribute to genetic diversity of plants Products of coevolution -can be quite specific -some yucca plants pollinated by only one kind of moth -but: most plant-pollinator interactions less specific Concepts -adaptation, advertising, strategy, beauty, deception, coevolution Remember -organisms - plants & animals (the latter excepting humans) - do not “plan” or “think about” or “design” to be deceptive or attractive or to “cheat” --------------------------------------------------------------------------------------------------------------------------------------------------------- SARS (severe acute respiratory syndrome) -appearance in southern China and coverup -spread to Hong Kong, then other countries -origins: Civet cat -importance of Asian customs, global travel, global cooperation, and global panic H1N1 -swine flu -originated in pig farm in Mexico -highly contagious -symptoms: chills, fever, sore throat, severe headache, coughing, lethargy, discomfort -at highest risk: people under age 24 -60 million Americans received vaccination -feared up to 90,000 Americans would die -55 million infected -250,000 hospitalized -11,000 people died -conclusion: a pandemic that didn’t happen Influenza in perspective: deaths -1918 Spanish Influenza: 50 million deaths -1980s - present AIDS: 30 million deaths -Black Death: 25 million deaths -SARS: 700 deaths Drugs to treat viruses -lag behind those developed for bacteria Why Darwin gets credits for theory -first with the idea -precedence in science/everywhere -elaboration & immense support After Darwin: what have we learned? -examples of natural selection working -change is genetic -population genetics firms up Darwin’s insights -species selection? -changes not constant through time Microevolution: changes in the genetic structure of populations -microevolution: small evolutionary changes, those that result in allele & genotype frequencies in a population Four causes of changes in genetic structure of populations -natural selection -mutation -gene flow -random genetic drift Natural selection: ex1 -have change in proportion of alleles for brown & blue eyes in the gene pool Mutations -change in an organism’s DNA -new alleles on which natural selection will work -occurs when cells make mistake in replication -they occur randomly -most are bad or detrimental Significance of mutations -original source of genetic variation that serves as raw material for natural selection Mutations from x-rays -may get in overexposure -from too much ultraviolet radiation - producing cancers -won’t be passed on to offsprings Gene flow -migration between populations common -metapopulation: a population divided into subpopulations, among which there are occasional exchanges of individuals Random genetic drift -chance events that alter gene frequencies -greatest effect in small populations -law of probabilities and large numbers -effect on rare genotypes -alleles become fixed Genetic drift: point to remember -because it is a random process, different results from generation to generation Population bottleneck -large populations can have allele frequencies changed -can come about through natural or human disaster -most genotypes may not appear --------------------------------------------------------------------------------------------------------------------------------------------------------- Founder effect -genetic drift in which rare alleles are occurring at a higher frequency in the general population -Amish example: small population and considerable inbreeding, allele for dwarfism and polydactylism Factors that facilitate evolution -two processes allow natural selection to speed up -sexual reproduction & nonrandom mating (assortative) Sexual reproduction -recombination of genes - more or less random -result: endless variety of genotypes -result: differential possibilities now available for natural selection to work on Nonrandom mating -also known as assortative mating -tall individuals mate with tall individuals, those in sororities mate with those in fraternities, rich marry rich Result of sexual recombination & nonrandom mating -remember: they open up possibilities for change in gene pool in subsequent generations Social darwinism & eugenics -Herbert Spencer -crude idea of “survival of the fittest” -eugenics movement in U.S. 1919-1950 -Nazism and Aryan nation brotherhood Eugenics -the active promotion by humans of particular traits in a human population -underlying belief: those selected are better adapted Eugenics & social darwinism -better adapated in what sense? -do better in a capitalist society -commit fewer crimes -have fewer genetic defects -are more intelligent -what else thought desirable? -suppression of “inferior” genes -- IQ tests -suppression of certain “races” and ethnic groups -those who wanted to intermarry -how done? -social policies, institutionalization, sterilization -who determines? -the rich & powerful, those who control social institutions -program promoted by: -state’s civic leaders -planned parenthood founder Margaret Sanger -L.A. Times publisher, Harry Chandler -Caltech head: Robert Millikan Eugenics and California -what California did -the third of 30 states in nation to legalize sterilization of insane and feeble-minded -promote programs that resulted in 20,000 people being sterilized -who was targeted? -men & women equally -foreign born more than natives -African-Americans more than Caucasians -those with mental illnesses or large families Normalizing selection -also known as “stabilizing selection” -reduces variation around mean or average -does NOT change the mean or average -characteristic of most populations Directional selection -Selection for “extreme” individuals -may occur in either direction -when changing environment -stabilizing selection may set in -direction of directional selection may change Disruptive selection Tigons and ligers -tigons: African lions and Asian tigers are obviously geographically separated, but they do mate in zoos -when the father is a tiger, the hybrid is called a “tigon” and hybrids are fertile Temporal isolation -occurs when the mating period of two species does not overlap -characteristic of most plants -different times of days, different seasons -note example of frogs Mechanical isolation -size and shape of reproductive organs may be crucial -insects: great diversity in, particularly among males -flowering plant morphology: small differences can prevent bees from transferring pollen from another plant Gametic isolation -remember: gamete = haploid reproductive cell -sperm of one species is not attracted to eggs of another species -appropriate chemicals not released to allow sperm to penetrate egg -sperm might function poorly in reproductive tract of another species Behavioral isolation -lack of sexual attraction between sexes -unwelcome or “unattractive” courtship rituals -could be based on chemical signals -pheromones in humans, for example Types of postzygotic mechanisms -those that operate after mating has occurred -hybrid zygote abnormality Hybrid zygote abnormality -zygotes fail to mature normally -abnormalities may develop that prevent successful mating -may die during development -- lethal genes Hybrid infertility -hybrids may mature normally, but be infertile when they attempt to mate -recall example of mule: offspring of a female horse and a male donkey -mules are vigorous but sterile: produce no offspring Low hybrid viability -offspring have tougher time surviving -may do well first generation but not well beyond that Incomplete reproductive isolation -contact is reestablished before genetic differences accumulate -gene pools can quickly combine and no new species is formed Geographical hybrid zones -zone where species interbreed only when in contact in one area -example of warblers -townsend warblers and hermit warblers hybridize -both breed in conifer forests and no boundaries at hybrid zone -hybrid zone shifting southward -- townsend warblers replacing hermit warblers -- why? -TWs: more aggressive -TWs: better at attracting mates -TWs: ability to maintain territory Evidence for evolution -comparative anatomy -embryology -biogeography -molecular biology -all are complementary Evidence from comparative anatomy -homologous structures: similarities that stem from having a common ancestor -can be homologous even though functions are different Types of homologous structures -anatomical: as noted -behavioral: e.g., bird songs, sexual posturing -molecular: nucleotide sequences in DNA Appearances can be deceiving -wing bones of bats and birds seem to be homologous -ancestral organism: amniote -wings NOT homologous -bird wings -- dinosaurs; bat wings -- mammalian ancestor Convergent evolution -recall example of wings that are not homologous -thus analogous structures: same function, but do not share a common ancestor -evolved to do same thing, but with different origins -cacti and spurges -similar appearance -both spiny flowering plants -cacti -- evolved in America -spurges -- evolved in tropical Africa --------------------------------------------------------------------------------------------------------------------------------------------------------- Evidence from embryology -organisms contain evidence of their evolutionary history -vestigial structures, embryological development -evidence in embryos not apparent in adult organisms -ex: all vertebrates have pharyngeal pouches in throat region in some stage of development Evidence from molecular biology -plants and animals all share common characteristics at molecular level -genetic code passed on through tree of life -can compare DNA and protein patterns to determine degree of relatedness Fossils - what are they? -hard shells, bones, and teeth that have been preserved in sedimentary rock -generally found in anaerobic (w/o oxygen) environments -most organisms die elsewhere -most not actual remnants Other fossils -species preserved in amber -species preserved in ice, tracks, eggs, dung -fossil record very incomplete, but some lineages well represented: horses Traditional fossils (link different taxa) -fish and land vertebrates -dinosaurs and birds -land mammals and whales What the fossil record reveals -great regularity -particular types in rocks of specific ages -new organisms in younger rocks -relative age only until radiocarbon dating -extinction the fate of all species Fossils - how many? -estimated 300,000 described -estimated 200,000 marine animals with hard skeletons -very selective record -how many exist? Radiometric dating Large eras -Precambrian Era (4.6 bya - 550 mya) -life exclusively uni-cellular for most of Earth’s history -02 virtually absent from oceans & atmosphere for 2 billion years after life -Paleozoic Era (550 - 245 mya) -origin of animals (land animals, plants fungi) -diversification of fish, amphibians, insects -Carboniferous Period - origin of seed plants and reptiles -rapid increase in animal diversity in fossil record -what caused Cambrian explosion? -emergence of predator-prey relationship -enough oxygen to support greater metabolic activity -emergence of particular genes (Hox genes) -Paleozoic 3 major extinctions -all experienced a drop in sea level -Permian extinction had most severe drop -ends with Permian extinction: loss of almost all multi-cellular life forms -90% extinction rate of species -climate warms -Antarctica forested -super-continent Pangaea formed -Mesozoic Era (245 - 65 mya) -mostly hot, humid -radiation of reptiles, origin and radiation of dinosaurs -origin of flowering plants, birds, mammals -Cenozoic Era (65 mya - present) -cooler, drier -radiation of birds, mammals, angiosperms, insects -origin of primates (30 mya) -Pleistocene, ice age (1.8 mya) -Earth cools, life shifts to equator -hominids appear & extinctions of large mammals and birds in America & Australia Pangea -250 mya, continents fused together -drop in sea level, change of ocean currents Role of extinction in history of life -mass extinction = account for only small proportion of all extinctions -large impact on radiation of taxa -background extinctions = occur during normal times -life expectancy of species varies among taxa -extensive volcanism and large bolldes(?) often implicated -how occur? -dust/ash “winter” followed by depletion of ozone layer and greenhouse effect Multiple factors account for extinctions -movement of Earth’s continents -tectonic changes, volcanism, meteorites -oceanic changes -climatic changes K/T extinction -50% + marine life -dinosaurs -impact hypothesis: iridium an element common in meteorites -continental drift How Earth changes over time -unidirectional change -1. rate of continental movement declined -2. free oxygen has increased -periodic change -sea level -volcanism -distribution of organisms -climate change: hot, cold, humid, dry