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Introduction to Evolution and Genetics > Out of Africa > Flashcards

Out of Africa Flashcards

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Biology 101 flashcards
1
Q

What is the Out of Africa concept?

A

Concept that humans have moved from an African point of origin and spread across the world.

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2
Q

What questions are associated with the Out of Africa concept?

A
  • where did humans move to
  • how often was there migration from Africa
  • was there hybridisation, how often and between whom?
  • were there any bottlenecks
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3
Q

What are the two competing hypotheses?

A

The Out of Africa Hypothesis and the Multiregional evolution hypothesis.

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4
Q

Describe the multiregional evolution hypothesis.

A

we evolved after migration of H. erectus from Africa with differences in racial features explained by a long period of evolution.

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5
Q

Describe The Out of Africa Hypothesis.

A

we originated as H. sapiens in Africa and have recently diverged since

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6
Q

How long ago is it estimated that humans were solely in Africa?

A

1 million years ago.

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7
Q

How long ago is it estimated that humans diverged from Africa?

A

0.1 million years ago (100,00 years ago)

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8
Q

What hypothesis does mitochondrial dna analysis point towards?

A

mitochondrial DNA analysis points to the Out of Africa hypothesis yet some palaeontologists claim to see features in archaic humans that match those in present day populations in the areas where archaic fossils have been found.

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9
Q

Whats a method used to explain human origins?

A

looking at differences in DNA - most early work was done on human mitochondrial DNA.

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10
Q

Why was early work on explaining human origins done with human mitochondrial dna (mtDNA)?

A

1 – it’s a good source of variation – the mtDNA genome mutates at a faster rate than the nuclear genome

2 – it’s a good source of DNA – more copies per cell

3 – it does not undergo recombination

4 – inherited purely down the maternal line

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11
Q

What is mtDNA?

A

Mitochondrial DNA

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12
Q

What are the major parts of mtDNA used for phylogenetic studies?

A

the major parts of the mtDNA genome that are used in phylogenetic studies are the cytochrome b oxidase gene (Cyt b) and the non-coding D-loop region.

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13
Q

Where is the massive rainbow phylogenetic tree taken from?

A

this phylogenetic tree is taken from mitochondrial DNA haplotypes.

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14
Q

What are branches on the left of the tree coloured to reflect?

A

on the left the branches of the tree are coloured to reflect the haplotype category.

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15
Q

What are branches on the right of the tree coloured to reflect?

A

on the right the colours reflect geographic origin.

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16
Q

What does the massive rainbow tree suggest?

A

the tree suggests that there is a greater amount of variation in those haplotypes found exclusively in Africa.

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17
Q

What does greater variation of the tree suggest?

A

the greater variation suggests an origin for Homo sapiens in Africa as all other mitochondrial haplotypes are more closely related to each other and therefore must have diverged later.

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18
Q

When did the Out of Africa theory start being used?

A

This theory arose once molecular evidence/data began being used.

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19
Q

What arguements are there about neaderthals and homo sapiens?

A

arguments persist over whether Neandertals are a separate species or the same species as us.

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20
Q

Was there interbreeding between homo sapiens and neanderthals?

A

Yes

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21
Q

Similarities between neanderthal genes and homo sapien genes?

A

around 4% of genes of Europeans are found in Neandertals - so there must have been some interbreeding.

22
Q

Differences between neanderthal genes and homo sapien genes?

A

both our Y chromosome and mitochondria postdate a human/Neandertal split. Neanderthals do not have them.

23
Q

How are we able to estimate when humans migrated from Africa?

A

because we can see which populations are more divergent from others and we can use the molecular clock to estimate times of divergence/isolation we can give an estimate of when humans migrated from Africa and colonised other parts of the world.

24
Q

Why could our ancestors not pass through the Sahara?

A

Change in environment made the Sahara a less impassable environment for a while.

25
Q

How did our ancestors get out of Africa when the impassable Sahara is in the way?

A

Coastal and swim

26
Q

Approximately how many years ago did humans reach Europe from Africa?

A

40,000 years ago

27
Q

Approximately how many years ago did humans begin to migrate from Africa?

A

0.1 million years ago (100,000 years ago)

28
Q

Approximately how many years ago did humans reach the Americas from Africa?

A

15,000 to 35,000 years ago.

29
Q

Approximately how many years ago did humans reach Asia from Africa?

A

60,000 years ago

30
Q

Approximately how many years ago did humans reach Australia from Africa?

A

50,000 to 60,000 years ago

31
Q

Why did distinction reduce after migration of humans out of Africa?

A

Migration (and gene flow) was limited for most of time before migration.
This allowed populations to become distinctive (as a result of local adaptations/sexual election?) and look very different.
Migration and random breeding now very high, so distinctions reducing.

32
Q

Details about Denisovans and Neanderthals.

A

Denisovans believed to have split from Neanderthals in 470,000 – 190,000 years ago in Siberia. Only few fossil fragments found but able to recover DNA. Sufficiently distinct to have been recognised as a species/subspecies.

33
Q

What is a bottle neck and when does one occur?

A

A genetic bottleneck occurs when a population is greatly reduced in size, limiting the genetic diversity of the species.

34
Q

Was there Hybridisation with Neanderthals and Denisovans?

A

Yes

35
Q

What was the bottle neck for Neanderthals and Denisovans?

A

supervolcano – MtDNA, down to about 1000 individuals.

36
Q

How long ago was the bottle neck of neanderthals and denisovans?

A

50,000 years ago.

37
Q

Where was the supervolcano located?

A

Lake Toba (Sumatra)

38
Q

When was the first briton beleived to appear in england?

A

10,000 years ago. (apparently)

39
Q

Why are historical distinction between biological races reducing?

A

Migration now much more common, so historical distinctions between biological races are reducing.

40
Q

When might genetic differences arise?

A

Genetic differences may arise when there is genetic isolation between populations.

41
Q

How might genetic isolation between population occur?

A
  • Minimal migration
  • Can occur when in same population but small breeding groups so effectively no migration of alleles between ends of population.
42
Q

What effects does genetic isolation cause?

A

Founder effects and bottleneck effects

43
Q

Define the founder effect.

A

In population genetics, the founder effect is the loss of genetic variation that occurs when a new population is established by a very small number of individuals from a larger population.

44
Q

What population genetic factors does genetic distinctiveness have to allow for?

A

Migration
Selection
Genetic drift (population size, founder effects, bottleneck effects)
Random breeding (increases gene pool, less chance of extinction)
Inbreeding
Assortative mating (increases homozygosity, increased fitness?)

45
Q

How does genetically inherited traits change from one geographic area to another?

A

genetically inherited traits change graduallyin frequency from one geographic area to another.
e.g, type B blood group allele generally increases from west to east in Europe.
This is known as Continuous distribution (Clines): migration.

46
Q

How does discontinuous distribution occur?

A

inbreeding, founder effect, bottleneck effect

47
Q

Give an example of discontinuous distribution?

A

Isolated area with low B allele frequency compared to surrounding areas.

48
Q

According to the Human Genome Project, how identical are humans at the DNA level today in percent?

A

In 2003, Phase 1 of the Human Genome Project (HGP) demonstrated that humans populating the earth today are on average 99.9% identical at the DNA level.

49
Q

Is there a genetic basis for race?

A

Because humans DNA are 99.9% identical, there is no genetic basis for race, and there is more genetic variation within a race than between them.

50
Q

“There is more genetic difference…

A

…within a race than between them”

51
Q

Is race a social construct?

A

Due to phase 1 of the Human Genome Project and its findings (as described in the other brsc cards) it is now widely accepted that ‘race’ is a social construct – used to justify slavery, colonization etc – this is 19th Century Biology…

52
Q

What is race a social construct used to justify?

A

used to justify slavery, colonization, etc.

Introduction to Evolution and Genetics (18 decks)

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