A biological investigation Understanding Race A biological investigation

Can you tell someone’s race by looking at their genes? Our guiding question Is race biologically/genetically based? What do you think? Can you tell someone’s race by looking at their genes?

Assumptions about human variation and the notion of race Traits are represented by a small number of distinct categories e.g. blue eyes vs. brown eyes Traits are connected One trait associated with a race predicts the presence of other traits There is greater genetic variation between races rather than within races

Describe what you see…without explaining Yao Ming and Jeff Van Gundy Willy Shoemaker and Wilt Chamberlain

Human Genetic Variation is real: How does DNA lead to traits?

Human Chromosomes

Assumption #1: Traits are represented by a small number of distinct categories COMPLETE DOMINANCE

Assumption #1: Traits are represented by a small number of distinct categories INCOMPLETE DOMINANCE: BLENDING CODOMINANCE: BOTH ALLELES EXPRESSED

Assumption #1: Traits are represented by a small number of distinct categories POLYGENIC TRAITS: TRAITS CONTROLLED BY MULTIPLE GENES MULTIPLE ALLELES: Genes with three or more alleles, but an individual can only possess 2. HOW MOST TRAITS ARE CONTROLLED -HEIGHT -WEIGHT -SKIN COLOR -BODY SHAPE -HAIR COLOR -EYE COLOR

Polygenic (many gene) Inheritance Example of a polygenic trait: human skin color For example: Three known genes that are all co-dominant Some contribute to light color (lowercase), less melanin, and some to dark (upper case) If two people with medium melanin levels have children what possible combinations of genes can they pass on to their kids?

Conclusion about Assumption #1 What can we conclude about the following statement? “traits are represented by a small number of distinct categories” Answer: Most traits exhibit continuous variation and there is no clear place to designate where one race begins and another ends

Assumption 2: Traits are connected One trait associated with a race predicts the presence of other traits For example: skin color is correlated with hair and eye color (these are one of the few examples) We are unable to predict virtually any other trait based upon another traits (like skin color)

Trait connectedness? In the United States sickle cell anemia is often portrayed as a “black disease”. Is skin color and sickle cell connected?

Distribution of malaria Distribution of sickle cell

Heterozygote Advantage and Sickle Cell

Homozygotes for the r allele suffer from sickle cell anemia, but homozygotes for the normal allele R are susceptible to malaria. Therefore, in areas where malaria is common, the heterozygotes Rr have an advantage over both homozygotes. How will natural selection act on these alleles?

Conclusion about Assumption #2 What can we conclude about the following statement? “One trait associated with a race predicts the presence of other traits” Answer: Human biological variation involves many traits that almost always vary independently. Variation is geographically-based, not “race”-based.

Assumption 3 There is greater genetic variation between races rather than within races

http://www.understandingrace.org/humvar/race_humvar.html

Conclusion about assumption 3 What can we conclude about the following statement? There is greater genetic variation between races rather than within races Answer: Genetic variation within so-called races is much greater than the variation between them. In other words, there is more genetic variation between individuals in a population than across continents.

Classifying people by their traits http://www.understandingrace.org/humvar/spectrum.html

Conclusion: There is no way to consistently classify human beings by race

The Mismeasure of Man (1996) by: Stephen Jay Gould “The impact of human uniqueness upon the world has been enormous because it has established a new kind of evolution to support the transmission across generations of learned knowledge and behavior. Human uniqueness resides primarily in our brains. It is expressed in culture built upon our intelligence and the power it gives us to manipulate the world. Human societies change by cultural evolution, not as a result of biological alteration. We have no evidence for biological change in brain size or structure since Homo sapiens appeared in the fossil record some fifty thousand year ago…All that we have done since then—the greatest transformation in the shortest time that our planet has experienced since its crust solidified nearly four billion years ago—is the product of cultural evolution. Biological evolution continues in our species, but its rate, compared with cultural evolution, is so incomparably slow that its impact upon the history of Homo sapiens has been small. While the gene for sickle-cell anemia declines in frequency among black Americans, we have invented the railroad, the automobile, radio and television, the atom bomb, the computer, the airplane and spaceship” (p. 354).