Unformatted text preview: IB35ac Class 13: Genetics: Comparing amounts of variation Now we know that there is genetic variation within our species, and that evolution and the diaspora of our species has shaped this variation. But just how much variation is there? Today we'll look at other species of primates and other animals to see if human genetic variation is a lot or a little. IB35 Human Biological Variation Class #13 Assessing Genetic Diversity Interspecific Intraspecific Topics for today:
Genetics: Comparing variation 30,000 genes in Humans Genetic Similarity Human: Human ~ 99.9% Human: Chimpanzee ~ 98.7% Human: Gorilla ~ 98.4% Human: Mouse ~ 85% Human: C. elegans ~ 74% Human: Banana ~ 50% Human: Daffodil ~ 35% What does it mean to be 98.7% chimpanzee? How are these estimates calculated? Proteins DNA hybridization DNA sequences
A T C C T T A T
human DNA sequence Look at mice... A T G C T G A T
gorilla DNA sequence Estimates from: http://en.wikipedia.org/wiki/Genomics Process of establishing a non-covalent, sequence-specific interaction between two or more complementary strands of nucleic acids into a single hybrid Measuring the effects of base incompatibility by quantifying the rate at which two strands anneal can provide information as to the similarity in base sequence between the two strands being annealed DNA hybridization
human DNA Human chromosomes separated human p DNA strand Combined humangorilla DNA gorilla DNA separated gorilla DNA strand Mouse chromosomes Heat end product and calculate energy needed to break product 1 But all regions are not equal... Coding versus non-coding x5-10 faster Differential mutation rates mutation rate than nuclear DNA mtDNA Using this information to build phylogenetic trees Back to allele frequencies Which one is more distant?
(which two are most similar?) Ans: A and B Population A = 0.70 Population B = 0.75 Population C = 0.50 A B C Length of the line = Genetic Distance Genetic Distance: Number of mutations that differentiate the two Dendrograms ->Genetic Similarities ->No time scale Tick Lion Baboon Chimp Human Relative time ->Phenotypic Similarities ->Does not indicate amount of evolutionary time
Horizontal Distance don't count -> 1-12 = 11-12 Cladogram ->Higher mutation rate ->Number of mutations not evolution Tick Lion Baboon Chimp Human Actual time Phylogeny ->Cladogram with time ->Branch lengths are proportional to amount of "time" separating taxa 2 Gorillas
Genus: Pongo Genus: Gorilla Genus: Pan Genus: Homo orangutans gorillas chimpanzees & bonobos humans Gorilla gorilla beringei (Mountain Gorilla) Gorilla gorilla gorilla (Western Lowland G ill ) (W t L l d Gorilla) Gorilla gorilla graueri (Eastern Lowland Gorilla) ->Endangered ->Don't drink water, get water from diet ->600 left in the wild ->Mostly vegetarian, eat insects occasionally ->Sexual Dimorphism ->Long hair ->Live in elevated areas ->Low Elevation ->Middle Elevation
One Taxonomic Option: Gorilla gorilla beringei Gorilla gorilla gorilla Gorilla gorilla graueri Another taxonomic option: G. gorilla gorilla (in red) G. gorilla diehli (in green with arrow) G. beringei graueri (in blue) G. berinei beringei (in orange with arrow) ->50-200 members in a group ->Female dominated ->Age span: 40 years ->Very little sexual dimorphism ->Dark skin Chimpanzees Pan paniscus (bonobos) Pan troglodytes (the "common" chimpanzee) From: Eriksson et al. 2004. Molecular Ecology 13: 3425-3435 Geographic distance (taking into account natural boundaries) similar to genetic distance
->Light skin ->Similar diet to Bonobos, but hunt ->Physically bigger than Bonobos ->Male dominated 3 hominids Ref: Krings et al. 1997 Cell ->Humans have less diversity ->We haven't been around as long as the other species From: Jobling et al. 2004. Human Evolutionary Genetics, p. 222. Using DNA sequencing African Ape Genetic Diversity mtDNA diversity within bonobos is intermediate between that of humans and chimpanzees (Pan troglodytes) mtDNA diversity within bonobos is comparable to what is found within chimpanzee subspecies, which is generally a bit more than that found within humans Conclusions for today Genetic diversity can be assess several ways (directly, indirectly, or by proxy) Compared to our closest living relatives, g p , genetic diversity found y the great apes, the g within humans is comparable to that of their subspecies. But wait a minute... 4 Different Human Populations ->Correlation between geographic distance and genetic distance Previous Interpretation Richard C. Lewontin A B C C A B
Lewontin's conclusion "Problem of Genetic Diversity" ->85% of variation overlap between races ->7-8% attributable to racial differences ->Essentially, races don't exist ->Based on sampling proteins ->Biased as most of the genome doesn't code for proteins Emerging view Implications... Suggests Neanderthals are a sub-species of Humans Jonathan Marks and Neandertals Should you allow social implications to influence your scientific interpretations? Sh ld we d fi species b Should define i based on d genetic diversity? C A B
Lewontin's conclusion 5 ...
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- Spring '08
- DNA, Gorilla, Hominidae, Gorilla gorilla gorilla, Human evolutionary genetics, Richard C. Lewontin