Class 12 - Oct 6

Class 12 - Oct 6 - IB35ac Class 12 Genetics mtDNA&...

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Unformatted text preview: IB35ac Class 12: Genetics: mtDNA & YDNA (mod hum orig) & DNA ancestry testing There is DNA inside and outside the nucleus. Mutations can happen in the genetic material in both places, but this happens at different rates. What are the implications of this? Introduction to four forces of evolution, HWE, and mtDNA and YDNA studies of modern human diaspora. We'll also talk about how these data are being used in these different forums, and touch on the ethical implications. Individual Grows up meiosis Chromosomes in the sperm cells IB35 Human Biological Variation Class #12 meiosis sex sex And on and on... Topics for today: mtDNA, YDNA & ancestry testing Individual Grows up meiosis meiosis sex Individual Grows up * read: - new ardipithecus fossil found What is a founder? A person who has a mutation that is then passed down through generations. Everyone with the mutation is related they have it in common because they are "identical by descent". Some more genetics Two types of DNA Coding Non-coding codes for proteins gene expression Found in nucleus Types of DNA Nuclear Autosomal chromosomes Sex chromosomes (X and Y) Mitochondrial DNA ->Y-DNA is passed solely along the patrilineal line, from father to son, ->mtDNA is passed down the matrilineal line, from mother to offspring (male&female) Found in mitochrondria Mitochondrial DNA (mtDNA) Provides the energy needed for cellular function Circular rather than linear 100s 1,000s f 100 1 000 of copies per cell i ll Sequenced completely in 1981 5-10 times faster mutation rate than nuclear DNA No recombination or segregation Maternally inherited (mostly) Cann, Wilson, & Stoneking 1987 study Contrast this with the Y chromosome... ->Looked at differences in mtDNA sequences ->Average difference approx 10-11 1 MRCA Most recent common ancestor What they found: Cann, Wilson, & Stoneking 1987 study Most variation is in African populations Variation of other populations is subsumed within th variation i Af i ithi the i ti in Africa All the different mtDNA lineages seen today, when you work backwards (i.e., "undo" the mutations), coalesce around 200,000 years ago... mtDNA Phylogeny of Modern Human Populations Neanderthals outgroup Africans Africans + everyone else Modern Human Origin Hypotheses Multiregionalism H. sapiens E. Euro ope Africa a Europ pe The Molecular Clock The molecular clock hypothesis holds that for any given DNA sequence, the rate of evolution is approximately constant over all evolutionary lineages. Requires calibration with fossils Replacement (Out of Africa) H. sapiens H. erectus POLYMORPHISMS ->Having multiple alleles of a gene within a population ->Usually expressing different phenotypes Asia a TIME H. erectus 2 ->Effect of bottleneck on highly polymorphic locus ->Gene pool prior to the bottleneck contained 20 different alleles ->Because of dramatic reduction in size of the pool, only four alleles passed on to subsequent generation ->In subsequent generations, gene pool grew until it attained its pre-bottleneck size, ->But random genetic drift eliminated three of the four alleles so that ultimately only one remained ->From this point on, polymorphism could only arise by slow accumulation of new mutations Bottlenecks Who is this mtDNA MRCA? She was NOT the only woman or person alive She is NOT the ancestor of all of our genes She did have a mother of her own She was not necessarily anatomically modern No 1-1 relationship between genotype and phenotype Group of similar haplotypes that share a common ancestor with a single nucleotide polymorphism (SNP) mutation mtDNA haplogroups Morphological change is not necessarily directly proportional t total ti l to t t l genetic change. Z & C M D & G B UK F, V, & H Y, T, & J N A X W L3 L2 L1 L0 outgroup Blue = Africa Red = Asian/Native American Green = Europe HAPLOTYPE ->Combination of alleles at multiple loci that are transmitted together on the same chromosome ->Set of SNPs on a single chromatid that are statistically associated Populations close to each other share haplogroups ->Migration 3 Y chromosomal lineages mtEve - 150000 years ago Y-Chromosome Adam - 60000 years ago Ancient mtDNA study 1997 Ref: Krings et al. 1997 Cell No overlap between h-h and h-n Things to think about: Morphological versus genetic evolution Why don't we see older coalescences? What are the implications of these models? d l ? DNA Testing Forensics Identification of victims Documenting presence at a crime scene Other times you might need to know Curiosity Figuring out who your relatives are/were Medical Diagnose a genetic disorder Warn of a predisposition Warn of chances of passing on a genetic disorder Indicate effectiveness of some drugs 4 Populations evolve, NOT individuals. Populations can be thought of in g terms of genes and allele frequencies. Evolution = changes in allele frequencies through time DIRECTIONAL SELECTION ->Natural selection favors a single phenotype ->Allele frequency continuously shifts in one direction The Four Forces of Evolution: Mutation (the only source of new variation) (acts to diverge populations directionally) (acts to diverge populations randomly) (acts like a `genetic glue' to hold populations together) Selection Drift Migration GENETIC DRIFT ->Change in the relative frequency with which an allele occurs ->Due to random sampling and chance Mutation Mutation refers to a change in the genetic message. This can happen two ways: 1. Changes in chromosomes 2. Changes in DNA sequence An example of directional selection: tooth selection: size in Pelycodus, an Eocene primate from N. America Another example of directional selection: selection: western corn rootworm The Idea of Genetic Drift LL = 49 Ll = 1 LL = 49,000 Ll = 1,000 N = 50 people N = 50,000 people 5 Generation 0 Generation 1 Generation 2 Generation 3 Generation 4 Generation 5 Generation 6 Generation 7 Generation 8 Generation 9 1 4 6 2 1 2 6 2 2 2 2 3 1 2 2 2 2 6 2 2 3 1 2 2 3 1 2 2 6 2 4 2 4 1 6 2 2 2 2 2 5 3 2 6 6 1 1 6 2 2 6 6 3 3 2 6 2 2 2 2 MIGRATION Population A alle frequencies: L = 0.99 l = 0.01 Population B alle frequencies: L = 0.01 l = 0.99 time merge alle frequencies: L = 0.50 l = 0.50 Drift The new mixed population 6 ...
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