EB23 Flashcards
(30 cards)
What is diversity in humans like
for a relatively young species (200,000 years) a lot of diversity can be observed within humans, however compared to other species its quite low
what is one of the main reasons for diversity in terms of phenotypes of humans
we are globally distributed which sets us apart from other primate species.
- humans can be found in variety of habitats
1. high altitude (tibet)
2. arid - ME
3. rainforest - pigmys kongho
4. cold - siberia, alaska
5. island populations: melanesians and polynesians: scottish
what is a a haplotype`
specific patterns of NSP more likely to be inherited together, variation across mulitple sites
what is a haplogroup
group of closely related haplotypes, patterns of haplotypes and haplogroups give us insights over what happens in the course of evolution.
what is the liklihood a new allele will reach fixation
1/2Ne
what is linkage equilibrium
no association between alleles even after recombination when they are adjacent on a chromosome
*when in equilibrium there should be no correlation between varients, however in reality there is always some degree of linkage
what is LD
the correlation between polymorphisms, if one polymorphism is present can predict likelihood of presence of linked allele
what is a selective sweep
when a new advantageous alelle enters a population and is selected for, all linked variation will increase in frequency intially as recombination takesa while to break up the linkage.
*reduction or elimination of variation amongst nts in the neughbouring DNA of a beneficial mutation, tend to increase LD.
what happens if all variation is lost in a selective sweep
recombination can not be seen as there is no variation to record such events. `
what is an incomplete selective sweep
excess of most common allele but not full takeover
what can natural selection be recognised by
- loss of genetic diversity around the selected site.
- increased LD around the selected site
- an excess of the most common allele
- deficiency of intermediate frequencys of alleles
- LD decays with time since selection began
what is lactase persistance
most humans cant digest milk as adults, however around 8000 years ago cattle domestication and pastoralism occured, correlated with lactase persistence.
LCT enzyme expression stops around weaning in all mammals except humans.
what can frequency of lactase persistance be correlated with
pastoral populations
what is lactase and how is it broken down
lactase is a dissacharide (gluc/galac)
to digest must cleave bonds between sugars via LCT enzyme
Describe lactase persistance evolution in humans
strong south north cline in persistance in europe, the more north the more persistance
ability to digest milk has happened atleast 5X independantly in humans, LD patterns can be seen around these variants.
what causes lactase persistance
mutation in promoter region of LCT MCM6 prevents expression being turned off.
SNPs in intron 13 and 9
How has global popualtion structure been inferred, what did this show
from 650,000 SNPs tying genetics to geography.
7 major ancestry components in humans identified
1. africa, 2. Mid east, 3. europe, 4. C.S asia, 5. E.asia, 6. Oceania 7. America
What do regions of the genome which differ between populations and have Fst>0.65 (alelle frequency difference) show
local adaptation
what did proportion of SNPS with Fst>0.65 show
proportion of SNPs with high Fst increases in those that are most functional, effecting gene expression or protein sequence *5’UTR or non synonymous mutations.
* this shows selection
how was skin colour variation investigated
Fst was calculated around loci involved in natural variation in pigmentation and plotted the maximum pairwise Fst between georgraphic regions in a 100kb window surrounding the SNP.
what is skin colour variation around the world the result of
lots of different genes, specific populations have selected for different variants.
* if there is a selective advantage for lighter skin further from the equator, varaint with light skin would be selected for.
Which variants and in which genes in a population is a matter of chance so get variable patterns of population differentiation.
What is an example of a highly differentiated gene
* how does this gene change around the world
EDAR
associated with multiple phenotypes.
1. a specific variant is completely fixed in E. asian populations (almost 100% will have a variant on both chromosomes), whereas the rest of the world will have the other variant at near fixation. *native americans who descend from East asians also have this variant.
2. rest of the world, almost 100% will have the other variant on both chromosomes.
What are the three hair variations and their morphologies under the microscope
- Asians: thick round cuticle hair: leads to straight hair
- Caucasians: thinner oval shaped cuticle: leads to wavier hair
- African: much thinner and flatter cuticle: tightly coiled thin hair
What type of hair is the EDAR variant associated with in east asian populations
very thick straight hair
