LEC 2 & 3 NOTES
LEC 2 & 3 NOTES ANT 160
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This 10 page Bundle was uploaded by Alexis Fulton on Wednesday February 3, 2016. The Bundle belongs to ANT 160 at University of Kentucky taught by Renee Bonzani in Winter 2016. Since its upload, it has received 71 views. For similar materials see Cultural Diversity in the Modern World in anthropology, evolution, sphr at University of Kentucky.
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Date Created: 02/03/16
Dr. Renée Bonzani Lecture Outlines for ANT 160: Cultural Diversity in the Modern World From Genetic Diversity to Human Variation •Why as humans are we so diverse? •Biological or Genetic Diversity •Mechanisms The basic strands or codes of life •The human body is made up of cells. Each cell has a nucleus. Within the nucleus are strands of what is known as DNA. •DNA = deoxyribonucleic acid. A double helix formation that contains the codes for the formation. •Nucleotides = the building blocks of DNA. There are four kinds of building blocks. Two of the bases are adenine and guanine and the other two are cytosine and thymine. These are arranged in a sequence with cytosine bonding only to guanine and thymine bonding only to adenine. •Figure. The separation and replication of DNA •From Figure 15.6 pg. 631. Keeton, William T. 1976. Biological Science. 3rd Edition. W. W. Norton & Company, New York. •Chromosomes = strands of DNA found in the nucleus. This structure is where the genetic information or genes are located. A human cell contains 23 pairs of chromosomes. Pairs of chromosomes that line up together are called homologous chromosomes . •Gene= basic unit of genetic information or inheritance. A portion of a DNA molecule that codes for some product, like a protein. •Figure. Human Chromosome Pairs •From Figure 13.5, pg. 561. Keeton, William T. 1976. Biological Science. 3rd Edition. W. W. Norton & Company, New York. •Alleles = different forms of a gene, when a gene exists in more than one form. Represented as a letter. Capital letter indicates dominance, small letter indicates recessive traits. On homologous chromosomes one may have the same alleles on each chromosome or different alleles on each chromosome •Homozygous = cells with the same alleles, either dominant, TT, or recessive, tt. •Heterozygous = cells with different alleles, Tt. •Genotype = the genetic composition, TT, tt, Tt. •Phenotype = the appearance represented by the genetic composition, TT and Tt (same appearance). 1 Combination and recombination •How genetic information is passed on in cells and from parents to offspring. •Mitosis = the division of cells. Nuclear division is first the complete replication of all of the chromosomes in a cell. Second, the distribution of a complete set of chromosomes to each daughter cell. Each daughter cell thus has 23 pairs of chromosomes (or 46 chromosomes) in humans or it is said to be diploid. •Diploid = having 2 sets of the same chromosomes. •Figure. Mitosis and cytokinesis in an animal cell. •From Figure 13.7, pg. 564. Keeton, William T. 1976. Biological Science. 3rd Edition. W. W. Norton & Company, New York. •Meiosis = the sexual division of cells. Each cell only contains half of the typical number of chromosomes. Chromosomes are not duplicated but homologous pairs are separated into different gamete cells. This separation occurs twice and results in four haploid cells. Each gamete cell has 23 chromosomes in humans. •Haploid = having 1 set of chromosomes. •Figure. Meiosis in an animal cell. •From Figure 13.18, pg. 572. Keeton, William T. 1976. Biological Science. 3rd Edition. W. W. Norton & Company, New York. •Gamete cells = sperm and egg cells. Sexual reproduction results in the recombination of the 23 chromosomes in the egg cell with the 23 homologous chromosomes in the sperm cell resulting in 46 chromosomes or 23 chromosome pairs in humans. The offspring has one set of the 23 chromosomes from the mother and one set of the chromosomes from the father. •Cloning = the replication of the chromosomes without the recombination of haploid gamete cells. Known to occur in asexual reproduction through mitosis. The result is that the offspring has the exact genetic makeup as the parent. Population Diversity, Migration, and Environmental Diversity From genetic diversity to human variation. •Evolution: change in the genetic makeup of populations How do genetic changes get passed from one individual (parent) to another (offspring)? •Mendelian genetics = Gregor Mendel was an Austrian monk who during the years of 1856-1868 performed experiments of ordinary garden peas. Results published in 1866 2 •He found that if he crossed a red flowered pea with a white flowered pea, the first generation was all red (F1 generation 100 % red). But in the second generation (F2 generation 75 % red 25 % white) the next generation had 3 red offspring and 1 white offspring. •Figure. Mendel’s experiments with peas. •From Figure 14.1, pg. 584. Keeton, William T. 1976. Biological Sciences. 3rd Edition. W. W. Norton & Company. New York. •This is how genes are passed on and the basis for genetic diversity in organisms. Possible Beginning of Lecture 3 How and why are genetic changes expressed in a population •Three factors to be covered herein that make individuals and populations different biologically: •Mutation= random change to DNA structure or genetic code •Natural Selection= the survival of the fittest. Acts on traits that benefit the adaptation of the species to their environment. •Genetic drift= changes in the gene pool purely as a result of chance, and not as a result of selection, mutation, or migration Sexual Selection may be discussed as well. See article by Frost (2014) •Mutations= One mechanism for genetic diversity to occur. Mutations are usually deleterious and do not get passed on to the next generation because offspring die before reaching the age of reproduction. However some diseases do not occur until after the reproductive age and can get passed to offspring. •Another example from Cavalli-Sforza, Luigi Lucas and Francesco Cavalli-Sforza. 1996. The Great Human Diaspora: The History of Diversity and Evolution. Perseus Publishing, Cambridge, Massachusetts. Question: why do recessive deleterious alleles that often result in lethal diseases remain in a population? •Example: •N = normal; T= mutation that causes the anemia: 3 N T N NN NT T NT TT •75 % normal (1 homozygous, 2 heterozygous) •25 % diseased (1 homozygous) •The heterozygous individuals have an advantage when affected by malaria. •Natural Selection •The Theory of Evolution by Natural Selection formulated by Charles Darwin and A. R. Wallace. Charles Darwin published The Origins of Species in 1859. •See information on Charles Darwin in Strickberger, Monroe W. 1990. Evolution. Jones and Bartlett Publishers, Boston. •Darwin and Wallace recognized the heritable variation as characters passed on by the parents. However, they did not know of Mendel’s work in which it was recognized that the unit of selection was the gene that behaves in a predictable manner. •They observed the persistence of characters that benefited the adaptation of the species to their environment. •Wallace and Darwin recognized the gradualism of environmental changes. •Evolution by means of natural selection was for Darwin and Wallace just the differential reproductive success of the species and adaptation to changing environments where adaptive characters are perpetuated and non-adaptive ones are eliminated •Darwin and Wallace did not know how the characters were produced. Only when genetics was developed was it possible to understand this. •Darwin and Wallace’s evolutionary process •Every species on this planet arose through the same process. •This process defines why a species looks and behaves a certain way. This process affects their morphology, physiology, and behavior. •Humans are subject to the same evolutionary process. 4 •Postulates •1- the ability of a population to expand is infinite, while the resources available to sustain the population are finite. This dynamic causes a struggle for existence among individuals as they compete for resources •2- organisms vary in their physical qualities; these variations allow some members to survive and reproduce more successfully than others (producing more offspring) in the same environment •3- these variations are inherited by offspring from their parents. Thus traits that confer advantage in survival and reproduction are retained in the population, and traits that are disadvantageous disappear •Natural selection preserves the status quo when the most common type is the best adapted. •Natural selection operates even over short time periods. •Natural selection operates even over short time periods. • Figure. Ear of maize (A), and pistillate spikes of Tripsacum (B) and Florida teosinte (C). From Figure 5.10, pg. 65. Mangelsdorf, Paul C. 1974. Corn: Its Origins, Evolution, and Improvement. The Belknap Press of Harvard University Press, Cambridge. Example: Changes from the probable ancestor of maize, teosinte (Zea mays ssp. parviglumis) to maize (Zea mays ssp. mays) may have only occurred over a few generations. • Figure. Archaeological evidence of corn’s evolution. (A) Three cobs or possible fragments of cobs found in the lowest levels of the excavations at Bat Cave, dated to ca. 2300 B.C. (B) A series of Chapalote-type cobs, the shortest being from the lower levels of Bat Cave at 48-60 cm with the longest cobs from the 12-24 inch levels. •From Figure 14.1, pg. 150. Photo from Mangelsdorf, Paul C. 1974. Corn: Its Origins, Evolution, and Improvement. The Belknap Press of Harvard University Press, Cambridge. •Genotypic and phenotypic changes from the earliest recovered small corn cobs (ca. 2 cm) to corn cobs over 12 cm in length may have taken less than 6,000 years. Example Bat Cave, New Mexico (earliest cobs date ca. 2300 B.C.)(Dick 1965; Manglesdorf et al. 1967). Where does selection operate? •Adaptation operates at the level of individuals who compete for resources and reproductive success. This is also important when we look at individual decision-making in terms of cultural adaptation. •Selection produces adaptations that favor individuals, not populations or species. •Adaptation favors the “fitness” of the individual. 5 What is Fitness? •Fitness: reproductive success of an individual. In other words, it is the number of offspring that an individual has •Fitness is different and should not be confused with fecundity which is the ability to produce offspring. •It is the accumulation and random selection of traits that produce adaptive changes and the evolution of species. This is called continuous variation. •Adaptation and fitness operate at the level of individuals. Summary •Natural selection, acting over time, can work only if each small change along the way is itself adaptive. •Evolution of species is a product of adaptation to changing conditions by a process of natural selection. •Natural selection can be summarized as the process of differential reproductive success of individuals. •Darwin’s explanation of variation can easily incorporate the genetic view that evolution typically results from changes in gene frequencies. The Importance of Migration and Adaptation in Genetic Diversity Mutations and the Environment: Why are they sometimes maintained in low frequency and not eliminated by natural selection? •The maintenance of different genotypes through heterozygote superiority of selection is called balanced polymorphism. •First example was thalassemia or Mediterranean anemia affecting the red blood cells (NN, NT, TT) where the heterozygote form (NT) has an adaptive advantage. •What is another example related to this? •Another Example: •Just as directional selection can reduce variety it can also maintain genetic variety by favoring a situation in which the frequency of certain alleles remain constant between generations. •Hemoglobin in Africa •Hb and Hb are two alleles for a gene that largely determines hemoglobin production in humans. 6 A •Homozygous Hb produces: normal hemoglobin •Homozygous Hb produces: lethal hemoglobin •Heterozygosity for this gene produces: sick S •It was discovered in certain populations in Africa, India, and the Mediterranean that that Hb allele existed at surprisingly high frequencies. •This is largely explained by the fact that the populations noted : Hb /Hb homozygote, normal red blood cells Hb /Hb heterozygote, deleterious non-lethal sickle cell syndrome S S Hb /Hb homozygote, lethal sickle cell anemia Person has 1 child, gets malaria and dies. Person has 1 child, gets malaria, recovers and has 3 more children. Person dies before having children. •This is an example of how the environment that these populations live in will affect their phenotype and genotype. •Further examples of how the environment affects genotypes and phenotypes of populations will follow. Effects of Migration and Adaptation on Genetic Diversity •Genetic Drift •Genetic drift= changes in the gene pool purely as a result of chance, and not as a result of selection, mutation, or migration. •Example = the genetic composition of the island of Pitcairn in the Pacific which was founded by 6 British sailors and a similar number of Melanesian or Polynesian women. The offspring were of all following generations were limited to the genetic composition of these founders. 7 •Founders’ Effect •Founders' effect = when only a few founders populate an area and their genetic composition is different from that of earlier peoples. A rare genetic disease in the general population may be quite common in these isolated groups •Another example = most Native Americans have O as their blood group. •see http://bloodcenter.stanford.edu/about_blood/blood_types.html New World blood types prior to A.D. 1492 Type O ca. 100% US Blood Types present day Type O 44 % Type A 42 % Type B 10 % Type AB 4 % 120% 100% 80% 60% Series 1 Series 2 40% 20% 0% Type O Type A Type B Type AB Graph illustrating the influence of gene flow and migration on blood types. Blue (Series 1) indicates approximate percentage of persons with blood types in the New World prior to A.D. 1492; red (Series 2) indicates percentage of persons with different blood types in the United States currently. •With migration into an area, new genetic material is introduced and one sees more continuous variation in traits and a modulation around the most adaptive traits. •Gene flow. •Gene flow occurs through interbreeding the transmission of genetic material from one population to another 8 •Gene flow inhibits: speciation, the form of new species •Speciation can be defined as the inability of different populations to interbreed. •Gene frequencies = the percentage of a population that has a particular allelic composition of a gene for a trait. Gene frequencies show continuous variation within a population. •Natural Selection acts on genetic variation in an environment only when it is expressed as phenotypic variation. In different environments, different genetic makeups are more adaptive to the population (those individuals with the greatest fitness) and will get passed on to offspring. Possible Beginning to Lecture 4 Natural Selection: Human Variation and Environment •More Examples of Human Variation and the Environment •All humans have the same basic genetic code (i.e. 46 chromosomes or 23 pairs of chromosomes). •Frequencies of the alleles they have for genes are different. •Natural selection works on the phenotype and therefore these differences are what we can see. •Example: Body Size •Body size and temperature. In colder climates it is better to be large to limit the amount of heat lost through the body. In warmer climates it is better to be smaller. When body volume increases, the ratio of surface to volume diminishes and heat generated by the body is lost more slowly. Bergmann’s rule = Larger bodies occur in colder climates while smaller ones are found in warmer climates. Allen’s rule = Longer protruding body parts are expected to occur in warmer climates. •Example: Body fat and temperature. •Humans are genetically well adapted to hot, dry conditions. There is no evidence of different genetic adaptations to heat in different populations. In relation to cold, humans have very low tolerance for cold. The protection to cold depends on the thickness of the layer of fat under the skin. •Example: Pigments of the Skin •Melanocytes produce melanin pigment. The more pigment in the skin, the darker the skin. •Explanations of why: •1) protection from skin cancer •2) dark skin protects the body’s folate store from destruction •3) UV initiates the formation of vitamin D. Deficiency in this vitamin can result in poor ossification of both bone and skeletal deformation or rickets 9 •Dark pigmentation keeps out harmful ultraviolet rays from the sun. Where is this particularly important? - The equator Figure. Witoto sellers at marketplace, Leticia, Department of Amazonas, Colombia (ca. 1998)(Photo by Renée M. Bonzani). •Light pigmentation allows ultraviolet radiation to be absorbed by the skin. Why and where might this be important? Near the article circle and very far north or south where there is not much heat and sunlight. Figure. Norwegians harvesting oats, Jølston ca. 1890. Photo taken by Axel Theodor Lindahl (1841-1906)/Norwegian Museum of Cultural History (From http://en.wikipedia.org/wiki/Norway). Possible discussion of sexual selection as an explanation of skin, hair and eye color. See Frost (2014). •Example: Lactose Intolerance •The term phenotypic adaptation refers to changes occurring to an individual organism during its lifetime that enhance its reproductive fitness. •Individuals from herding populations in Northern Europe and parts of Africa maintain their ability to digest milk (continue to produce the enzyme lactase) into adulthood, whereas people from other populations can digest milk (specifically, milk sugar, called lactose) only during childhood. •The fact that descendants of these herding populations who no longer herd continue to be lactose tolerant as adults indicates genetic adaptation to a milk-rich diet. Conclusions on Environment and Adaptation •One single origin for the species Homo sapiens. •All humans are the same species. •There are no races, just genetic variation that is related to adaptation to the environment including human influences. •There is no biological basis to create groups of population in terms of distinctive genetic characteristics. We can observe variations in gene frequencies but there are no exclusive genes relating a group by religion, geography, country/nationality, color or any category. 10
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