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Biological Anthropology On Cells, DNA, Proteins, and Populations Cell Theory • A set of explanatory principles used to understand cells • Cells are the smallest unit of life • Consist of smaller (non-alive) parts: organelles A Cell Two Types of Cells Somatic cells Sex Cells (gametes) • The vast majority of cells in our bodies • Only found in ovaries and testes • Reproduce through mitosis • Reproduce through meiosis Two Types of Cell Division Mitosis Meiosis • Occurs in somatic cells • Occurs in sex cells (gametes) • Produces 2 daughter cells • Produces 4 daughter cells • Genetically identical • diploid • Genetically unique • haploid Mitosis • Asexual reproduction • Occurs in somatic cells • Produces 2 genetically identical diploid daughter cells Meiosis • Occurs in sex cells (gametes) • Produces 4 daughter cells • Genetically unique • haploid Crossing-Over 6 wet A 5 dry # of fingers 6 cerumen dry O ABO group A 5 wet O Cell Division Mitosis Meiosis Karyotype • Species-specific set of chromosomes • Differs from species to species in terms of • The number of chromosomes • The sequences of genes contained in the chromosomes Human karyotype • 46 chromosomes • Arranged in 23 pairs • 1 set from each parent Human karyotype • Autosomes • Pairs 1-22 • Are homologous • same length • same sequence of genes (may be different alleles) Human karyotype • Sex chromosomes • Pair 23 •X & Y X longer than Y • XX – homologous • XY – partially homologous So what’s in a chromosome? Let’s take a look! A chromosome contains genes and genes contain… Deoxyribonucleic Acid • Present in all living organisms • Amount varies from organism to organism • Species can read each others’ DNA DNA • Sugar-phosphate backbone” • Bases are “rungs” adenine = thymine cytosine = guanine Genome the total DNA/genes of a species • Homo sapiens • app. 3,000,000,000 DNA bases • 35,000 – 40,000 genes • Honeybee – 300,000,000 DNA bases • Fruit fly – 13,600 genes • Bacteria – a few hundred to a few thousand genes DNA Replication • Produces two identical strands from one original strand • Each side of the original is a template for making a new copy of its complement The Three Problems 1. How is the variation present within a species at any time affected by the environment? Darwin 2. How is variation passed on from one generation to the next? Mendel 3. Where does variation come from? Watson & Crick But what are genes used for? Protein Synthesis • A two stage process • Transcription • Translation • Our players: • Messenger RNA (mRNA) – the locks • Transfer RNA (tRNA) – the keys • Ribosome (“locksmith) • Amino Acids Protein Synthesis • 1: Transcription messenger RNA (mRNA) copy of gene is made • mRNA copy leaves nucleus and goes to cytoplasm Protein Synthesis 2: Translation • mRNA copy is “read” by ribosomes • Ribosomes match tRNA to codons on mRNA Proteins: the End Result • One gene codes for one protein • Differences between individuals due (in part) to differences in their proteins Protein Synthesis, once again… • A two stage process 1) transcription 2) translation • The process whereby the DNA message is converted into a protein product for more information… Web sites http://www.dnalc.org/resources/ Key words • DNA replication http://en.wikipedia.org/wiki/ • Protein synthesis http://www.johnkyrk.com/ • DNA translation http://www.youtube.com/ • Transcription and now let’s turn to… Population Genetics Population • A (potentially) interbreeding group of organisms • (usually) a subset of a species “Populations” Differ How Should We Describe Populations? Monogenic Traits Polygenic Traits • Qualitative • Quantitative • Discontinuous graph • Continuous graph Use Polygenic Traits? • Advantage: often easily observable • Disadvantage: can change over an individual’s life time • Poorly suited for population studies Racism • A social/cultural phenomenon • Attempts to distinguish between human populations on the basis of polygenic traits • Used to justify hierarchies within society • Is not based on scientifically valid criteria Use Monogenic Traits! • Disadvantage: not always easily observable • Advantage: do not change over an individual’s life time • Useful in the study of populations • Genetic Markers = monogenic traits in which the genotype is known Genetic polymorphism When two or more phenotypes exist within a population that means that the population exhibits variation for that trait and variation is what makes evolution possible Adaptation a trait that increases an organism’s reproductive success What adaptation is being measured here? How might this adaptation increase an individual’s reproductive success? Adaptation (a classic example) The wing color of the Peppered Moth is a monogenic trait Adaptation produced by natural selection in the context of a particular environment A light variant mating with a dark variant Light and dark variants on light and dark backgrounds Adaptation produced by natural selection in the context of a particular environment Smokestacks during the Industrial Revolution Evolution defined drum roll please… A change in allele frequency from one generation to another This means that… the unit of selection is the individual while the unit of evolution is the population Population Genetics • Studies how evolution occurs in populations of organisms • Population – a (geographically localized) group of individuals in a species that share a common gene pool and tend to find their mates within this group What are the factors that could influence the evolution of our population? •Founder’s effect •Assortative mating • Positive •Natural selection •Mutation •Migration • negative •Genetic drift Founder’s effect • How well would we represent the population from which we are derived? • SoCal! Natural Selection • Do blondes have more fun (and more early onset skin cancer)? • Is it better to be redder? • Hereditary diseases, anyone? • Other possibilities? Mutation • Random mutations • Heightened mutation rates? • Cosmic rays? Uranium ore Migration • Do some people leave? • Do others arrive? • Did some “visit”? • Gene flow vs. migration Hypothesized migration pattern of the Pacific Islands Assortative Mating Positive Assortative Mating Negative Assortative Mating • phenotypically similar organisms • phenotypically dissimilar organisms • increases homozygosity • increases heterozygosity • decreases variation • increases variation Genetic Drift the random factor, or “joker in the deck” A genetic bottleneck reduces a population temporarily to very low levels, removing much of its genetic diversity. Mutiny on the Bounty by Robert Dodd (artist & engraver); 2 Oct., 1790 In 1790, 9 Bounty mutineers plus 18 Tahitians (six men, 11 women and a baby) fled to Pitcairn Island The Pitcairn Islanders today app. 60 people (the smallest democracy in the world!)