Lecture 23

Question 1

Contrast the multiregional emergence hypothesis and the recent African origin hypothesis
concerning the origins of humanity. What does each hypothesis predict with respect to the fossil
record? Which hypothesis is supported by human mitochondrial DNA? Explain.

Answer 1

MRE: multiregional emergence of humans from home-rectus across the world all at once an hypothesizes that the oldest human fossils should be found at each site of the independent origin

RAO: humanity evolved one time from eastern Africa and migrated out of Africa, hypothesize that the oldest human fossils should be found in Africa

RAO + admi xture with other hominin species is best supported by mitochondrial dna

Question 2

How similar/different are the genomes of two random humans?

Answer 2

any two random humans differ in 1/1000 bases in term of single nucleotide polymorphism

Question 3

Where is genetic diversity the highest for human populations? How does this idea tie into the
concept of serial founder effects?

Answer 3

genetic diversity is highest in African populations because as subsets of the African ancestaal populations migrated from Africa serial bottlenecking occurred where gnetic diversity decreased

Question 4

If we saw an Fst value for comparing populations A and B of 0.65 and an Fst value when
comparing populations A and C of 0.07, how would we interpret this result in terms of genetic
differentiation of these populations?

Answer 4

We would conclude that there is more genetic differentiation between populations A and B compared to between A and C.

if Fst=0 than they are not two distinct populations

Question 5

Why are phylogenetic trees of human populations misleading? Define reticulation in your answer.

Answer 5

Phylogenetic trees are misleading as they do not consider exchange of genes between the different species populations

Reticulation: is the horizontal mixture of genetic information between populations within a species that violates assumptions of phylogenetic trees.

Question 6

How do mitochondrial genomes partially circumvent this issue of reticulation?

Answer 6

mitochondrial trees combat reticulation as mitochondrial DNA does not undergo recombination events and is strictly maternally derived.

Question 7

Define mitochondrial Eve. Does the existence of mitochondrial Eve mean that any other females
that existed concurrently with this individual have no living descendants? Explain your answer.

Answer 7

Mitochondrial eve: a single woman who by which all mitochondrial genes are derived from.

This does not mean other females did not leave descendants, it instead means their mitochondrial DNA eventually went extinct.

Question 8

How old are the oldest fossils of anatomically modern humans? When did humans and chimps
share a common ancestor?

Answer 8

the oldest fossil of modern humans are 200,00 years old.

Humans and chimps shared common ancester 5-7 million years ago.

shared genomic information amonst great apes

Question 9

What is a conservative amino acid substitution? Are these expected to be common or rare if most
of the differences between humans and chimps are due to regulatory mutations?

Answer 9

Conservative amino acid substitution is the substitution of an amino acid across species that does not result in any protein expression changes ( similar to codon optimization).

These are expected to be common as they do not have any detrimentla effect.

Question 10

If you are looking at a particular nucleotide in a gene shared by gorillas, chimps, and humans, and
you see that gorillas and chimps have a G at this position and humans have a T. Which base is likely
the ancestral state? Define outgroup in your answer.

Answer 10

The ancestral state is likely G and humans independently derived the T allele making them an outgroup.

Question 11

How are we able to determine that humans interbred with Neanderthals and Denisovans?

Answer 11

By sequencing the dna of extracted fossils from denisovans and neanderthals there is evidence of admixture between humans and these other hominin species

Question 12

What are the three main hypotheses concerning the disappearance of Neanderthals?

Answer 12

1. humans drove them to extinciton through violence
2. Human drove them to extinction by outcompeting for resources
3. Humans were simply more numerous so when admixture occurred the diverged populations were mostly genetically human and had some neanderthal DNA.

Question 13

13. What is adaptive introgression? Provide a potential example of this occurring in humans.

Answer 13

Adaptive introgression is the transfer of genes from one lineage to another as a result of admixture and a subsequent selection of these advantageous alleles in the population that received them.

This occurred in humans. After neanderthals migrated from Africa many years before humans they developed immunity to certain east asian pathogens. When human later migrated to these same regions and admixture happened with neanderthals the advantageous alleles coding for immunity were transferred to humans and over time selected for.

Question 14

What does FOXP2 tell us about the likely language capacities of Denisovans and Neanderthals?

Answer 14

FOXP2 is a TF that encodes for language and speech abilities so while humans have two structural changes in the amino acid sequences for this gene compared to the great apes

neanderthals and Denisovans share these two structural changes as us which indicates they may have had similar language abilities as us.

Question 15

What does it mean to “humanize” the FOXP2 allele in mice?

Answer 15

In a study, the alle for the FOXP2 gene in mice was mutated to be more similar to humans. This helped the mice to learn to escape a maze faster and cuased changes in their vocalization

Question 16

What are two population genetic consequences of adaptive alleles spreading in a population?

Answer 16

When adaptive sales spread in a population :

1. there could be a subsequent increase in variants that are linked to the adaptive alleles
2. at that locus on the chromosome there will be a decrease in variation

Question 17

Did lactose tolerance arise once or multiple times independently? Defend your answer

Answer 17

Lactose tolerance arose independently in different populations as each population developed different mutations that elicited the same effect of lactase persistence. Considering these populations either relied on cattle or were pastoralists they evolved to have these mutations.

Question 18

Contrast convergent and parallel evolution.

Answer 18

convergent evolution is the independent development of different mutations across populations

parallel evolution is the independent development of the same mutations across populations.

Question 19

What is the main benefit of darker skin in equatorial environments?

Answer 19

The increased melanin in darker skin provides protect from UV rays that are in higher abundance near the equator

Question 20

What is the main potential drawback of darker skin at higher latitudes?

Answer 20

Darker skin at higher latitudes has a draw back as increased melanin where there are low UV levels hinders the harvesting of that UV to make vitamin d3.

Question 21

What are the three main applications of forensic genetics?

Answer 21

1. linking Crime Scene DNA to a suspect
2. paternity testing
3. identification of remains

Question 22

What are three criteria for a locus to be included in CODIS?

Answer 22

1. known chromosome locations and assorrt indepenndetly ( if they did not two markers would hav eoverlapping information)
2. must have multiple alleles of at most 25% frequency ( if it were greater, many people would be hojmozygous for the allel and it would not be informative of the indentiyof the individual)
3. consistent and reproducible PCR

Question 23

Consult table E.2 in the slides and the book and calculate the probability that a random individual
would have the following genotype assuming HWE

Answer 23

Homozygous for FGA= P^2=(.18*.18)=

Heterozygous for vWA= 2pq=(2.017.125)=

Heterozygous for D3S1358= 2pq(2.186.088)=

joint probability= .0324.00425 0.032736= 0.0000450774

Question 24

Consult table E4 and identify each CODIS marker that excludes F2 from being the father of the
child.

Answer 24

FGA: the 23 allele is maternally derived so the child 20 allele must have come from the father however f2 is heterozygous for 18 and 23 therefore it could not have been the father as it cannot pass down the 20 allele

vWA: child has 17,18 allele and because mother has 18,18 had to have gotten 17 allele from father

D8S1179: child has two 14 alles so father must have an 14 allele like the mother but he doestn

D16S539: child received 12 allele from mother so father must have 14 allele but he doesn’t

D21S11: child received 30 allele from mother as she does not have 28 allele. 28 allele has to have come from father however F2 does not have 28 allele.