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Chapter 14

chapter 14 - The Human Species: An introduction to Biological Anthropology.docx

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Esteban Parra

Chapter 14 – Study of Human Variation -the least amount of variation - the most amount of variation (existing in humans) 1) physical characteristics (ex. hair colour) 2) less observed characteristics (teeth) 3) Variation at the molecular level 3 common questions to ask when looking at human variation: 1) what is the pattern of variation WITHIN a population? - allele frequencies, what are genotypes and phenotypes = simple traits - what is the average value, and the range around this average value = complex traits 2) what is the pattern of variation BETWEEN populations? - do allele freq differ across populations? 3) why are there patterns of variation? *biological anthropologists study variation in terms of evolutionary forces and biocultural adaptations – * but individuals often discuss variation as RACE and ETHNICITY - people tend to classify and reduce variation by using averages or stereotypes – 2 goals of this chapter: 1) look at different types of variation 2) look at the global patterns of human genetic diversity Measuring human variation Variation: differences existing among people and populations - can exist in terms of physical traits – but also in terms of biochemical traits – ex. diff blood groups (A, B, O, AB) - can’t just look at physical observable traits because its 1) subjective – what u think is tall may be diff from someone else’s perspective 2) our categories of variation don’t show that traits are continous – ex. skin colour isn’t discrete categories, it is continuous 3) a lot of variation that exists cant be seen by observing Red blood cell polymorphism - a lot of info has been found about genetic traits by looking at red blood cells - RBC polymorphism include blood types and protein and enzyme types Polymorphism = genetic trait where at least 2 alleles have a frequency greater than 1% Blood type - different blood group systems have been found based on the types of molecules present on the surface of the red blood cells – ex. ABO blood type, MN blood type, Rhesus, Diego, Duffy and Kell blood group systems - different blood groups are identified based on different antibody-antigen reaction - antibody= substances that react to foreign substances Antigen = substance invading the body – which can stimulate production of antibodies - ex. AB blood group – Has 3 alleles – A, B, O – where A and B are codominant, O is recessive - anti-A (antibody) reacts to antigens A and AB – - if blood clumps to anti A antibodies but not B antibodies – it means that the person has type A blood Blood proteins and enzymes - genotypes for blood proteins and enzymes is found using a method called electrophoresis: lab technique – electric current seperates proteins – thus genotype can be determined - NEGATIVE (electricity flows ) POSITIVE Blood cells  also moves * all occurs in a gel *thus proteins fromm the blood move with electrons – at faster and slower rates - the distance they travel through the gel = determines genotype *diagram pg 361 – shows same thing HLA system = human leukocyte antigen system - variation in antigens are found on the surface of white blood cells = leukocytes - controlled by loci on chromosome 6 - important in bodys autoimmune response – HLA types determines if organ transplant would be successful - there are a lot of differences in HLA allele frequencies among human populations – good marker to see genetic similarity patterns - HLA antigens also associated with diseases like arthritis DNA ANALYSIS - with cheek swabs or hair sample – can see forms of variation by looking at DNA sequences Methods of DNA analysis - sources of variation: 1) RFLPs = Restriction fragment length polymorphisms – differences in the length of DNA fragments give a useful measure of human variation @ the molecular level - thus it’s a genetic trait produced when certain enzymes cut the DNA sequence into different DNA fragment lengths 2) looking at non coding DNA sequences that are repeated = microsatellite DNA - short repeated sections of DNA (2-5 bases) – number of repeats is variable - also called short tandem repeats – STR - ex. 5 repeats of CA – CACACACACA *long repeated unit of DNA = minisatellite 3) Alu insertion – a sequence of DNA repeated at different locations on different chromosomes - variations exist in terms of the presence or absence of a repeated sequence at a particular location 4) single nucleotide polymorphisms (SNP) – a position in the DNA sequence where it differs by one base = helps see linkage of traits – as well as genes which may influence disease susceptibility when comparing genomes - *sometimes also look at mismatches = differences between sequences – when comparing entire DNA sequences – help show genetic similaritiy and evolutionary history DNA haplotypes and haplogroups - due to linkage, DNA sequences that are close to each other on the same chromosome are inherited together as a single unit = combination of genes and DNA sequences = haplotype * can be common to exist within members of a family – ex. Thomas Jefferson + slave women = child? - haplogroups = looking at groups of haplotypes that share common mutations Ex. Different makes of cars = ex. Ford = haplogroups – has cars with similar common equipment – ex. radio And different models of cars = mustang = haplotypes Assessing different patterns of inheritance - most DNA is nucleur DNA = inherited from both parents – has potential for recombination - mitochondrial DNA = only inherited from mother – cant have recombination- same is true for DNA on a males Y chromosome – comes only from the father – cant have recombination *this makes it easier to look at mitochondrial DNA ancestry – because each generation only has 1 ancestor – mother inherits it from her mother – which gets it from her mother - same with Y chromosomes in male But with nucleur dna – the ancestors in each generation in the past – will double – because it comes from mom and dad –e ach time Complex traits - have complex relationship between genotype and phenotype – also are affected by growth and the environment - anthropometrics: measurements of the human body – ex. Head and face 2 common triats = weight and height - can also look at length of limbs – width of body at various parts - skinfold measure = how thick a section of skin and fat are which are pinched together = provides a way to assess body fat and nutritional status - measures taken on the human face and skull = length and width of the skull and face – by eyes, cheekbones and lower jaw – also on heirght and width of nose = craniofacial measures – help show relationships between human populations Skin colour - in the past – compared skin colour to set of tiles – but this is too subjective - now use a spectrophotometer – measures the % of light reflected back at different wavelengths – light skin – reflects more light back - to be able to get the true colour and not tanned colour – we look on the inside of the upper arm – Other measures - odontometrics = measurements of the size of teeth – - length (front to back) and width is measured using capiers – can also look at shaped incisors – ridges on the inside margins of front teeth – common in east asia and native American populations - dermatoglyphics – measurements of finger and palm prints – including type classification (whorls, loops, arches) and ridge line counts RACE AND HUMAN VARIATION - how do we describe patterns of variati
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