IB 110 Chap.3 Genetic Variation, Ancestry and Ethnicity
Genetic Variation, Ancestry and Ethnicity
Two concepts of race
The second lecture sets an essentialist concept of race against a population concept. In the essentialist picture, each race is a fixed type whose members share an inner essence. In the population picture, groups differ only in the average frequencies of gene variants, with wide overlap.
The course goes a step further and treats race as a social grouping, not a biological unit at all.
What the genome shows
The lecture gives the scale of the human genome, about 3 billion base pairs and 20,000 to 25,000 genes, and states that any two people can differ genetically more than whole populations differ on average.
People from very different ancestral and cultural backgrounds can sit close together on a measure of skin pigmentation, because pigmentation depends on a small portion of the genome.
The most visible trait is one of the least informative about ancestry.
The EDAR example
A 2013 study discussed in the lecture linked one variant of the EDAR gene to several traits often described as East Asian, including hair thickness and the number of sweat glands, and dated the mutation to about 35,000 years ago.
The lecture's point is that the variant is carried by only around half of the population it is associated with. A variant that half of a group lacks cannot define the group.
Ethnicity and ancestry
Ethnicity is a shared identity rooted in ancestry, language or culture.
The lecture notes that the only ethnicity the United States tracks is Hispanic, meaning origin in a nation colonised by Spain, and that Spanish links countries with little else in common. A 2015 Pew survey it cites found 17% of Hispanic adults saw being Hispanic mainly as a matter of race, 29% as ancestry and 42% as culture.
A genetic study of samples from Mexico, Colombia, Puerto Rico and Peru found very different mixes of African, Native American and European ancestry under one ethnic label.
When ancestry matters for health
The fourth lecture adds that narrow, linked ancestry can be medically important.
Around 6% of Ashkenazi Jews carry a mutation that raises colon cancer risk, and variants for Gaucher disease, cystic fibrosis and Tay-Sachs disease are more common in that community.
This is ancestry acting through specific genes, which is different from a broad racial label predicting disease.
Reading trait studies with care
When a news story links a gene to a group, check three things: how common the variant is in that group, how common it is elsewhere, and how many traits it actually affects.
Those three numbers usually turn a claim about a type of person into a more modest claim about frequencies.
What this chapter covers
- 01
Essentialist and population concepts
- 02
Genome size and individual variation
- 03
Why skin tone misleads
- 04
The EDAR V370A variant
- 05
Ethnicity and Hispanic origin
- 06
Ancestry mixes within one label
- 07
Linked ancestry and disease risk
Worked example · free
Decide whether a category is useful for predicting risk
- 2State the problem with broad categories.
- 2Explain why linked ancestry works better.
- 1Give a course example.
Key terms
- Essentialist Concept
- The view that each race is a fixed type whose members share an inner essence; the course rejects it.
- Population Concept
- The view that groups differ only in average frequencies of gene variants, with extensive overlap.
- Genetic Admixture
- The mixing of ancestries from different source populations within one person or group.
- EDAR Variant
- A variant of the EDAR gene linked to several hair and sweat-gland traits and carried by about half of the population studied.
Genetic Variation, Ancestry and Ethnicity FAQ
Are there genetic differences between races?
There are differences in the average frequency of some variants between populations, but the lecture stresses that two individuals differ more than populations do, so a racial label is a poor guide to any one person's genes.
Is Hispanic a race?
The lecture treats Hispanic as an ethnicity, meaning origin in a nation colonised by Spain. A genetic study it cites shows very different ancestry mixes across Mexico, Colombia, Puerto Rico and Peru under the same label.
When is ancestry medically useful?
When a narrow group shares specific variants at high frequency, as with the Ashkenazi Jewish community and colon cancer risk. The usefulness comes from the linked ancestry, not from a broad racial category.
Exam move
Make a three-column table headed race, ethnicity and ancestry. Under each, write the definition, one example from the lectures and one thing it cannot tell you.
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