HERITABILITY
Heritability is a direct correlation: It has a coefficient from 0 to 1. The more heritable a disease or trait is, the more the differences between people can be associated with genetic variation.
Correlation does not imply causation (without the manipulation of variables). Most heritability estimates are based on correlational studies of monozygotic and dizygotic twins.
See the chart below. Heritability estimates for certain diseases are listed from 0 to 1. Diseases that are “highly heritable” are close to 1, whereas diseases with “low heritability” are closer to zero. How might the chart better represent the correlation? That is, instead of saying that highly heritable diseases are “explained by genetics,” group differences are (circle all that apply):
a) caused by genetic variation
b) impacted by genetic variation
c) associated with genetics variation
d) linked with genetic variation
e) enhanced with each generation
f) tied to genetic variation
Image from http://blog.23andme.com/wp-content/uploads/2012/05/HeritabilityWithKids.jpg
0------1
List a highly heritable disease – a disease where group differences are connected to genetic variation.
List a disease with low heritability – a disease where group differences are connected to environmental variation.
0------1
When heritability is low When heritability is high
Environmental variability high Environmental variability is low
Differences associated environmental variation Differences associated with genetic variation
Different environments Same environments (growing up in barrel)
Examples:
1. The differences in identical twins are associated with
low heritability or high heritability 0------1
2. The differences between amputated people and those who have five fingers on each hand are associated with
low heritability or high heritability 0------1
3. The differences of identical twins raised in two separate countries are associated with
low heritability or high heritability 0------1
4. The differences in human-beings who wore earrings in the United States in the 1950s are associated with
low heritability or high heritability 0------1
5. The differences in people who live in a “rich country” where everyone eats what they want are associated with
low heritability or high heritability 0------1
6. The differences in people who live in a country with diverse situations (some eat poorly and some eat what they want) are associated with
low heritability or high heritability 0------1
References
Feldman, Alan (n.d.). Understanding Heritability. Retrieved from
http://apcentral.collegeboard.com/apc/members/homepage/45829.html
Myers, D. (2007) Psychology in Modules. (8th ed.). New York, NY: Worth.
Answers/Teacher Key
…Instead of saying that highly heritable diseases are “explained by genetics,” group differences are (circle all that apply):
c,d,f
a) caused by genetic variation
b) impacted by genetic variation
c) associated with genetics variation
d) linked with genetic variation
e) enhanced with each generation
f) tied to genetic variation
------
List a highly heritable disease – a disease where group differences are connected to genetic variation.
Any diseases to right of x-axis – have estimate closer to 1
List a disease with low heritability – a disease where group differences are connected to environmental variation.
Any diseases to left of x-axis – have estimate closer to 0
------
Examples:
1. The differences in identical twins are associated with
low heritability or high heritability 0--------1 ENVIRONMENTAL VARIATION
2. The differences between amputated people and those who have five fingers on each hand are associated with
low heritability or high heritability 0---------1
3. The differences of identical twins raised in two separate countries are associated with
low heritability or high heritability 0------1 ENVIRONMENTAL VARIATION
4. The differences in human-beings who wore earrings in the United States in the 1950s are associated with
low heritability or high heritability 0------1 GENETIC VARIATION
5. The differences in people who live in a “rich country” where everyone eats what they want are associated with
low heritability or high heritability 0------1 GENETIC VARIATION
6. The differences in people who live in a country with diverse situations (some eat poorly and some eat what they want) are associated with
low heritability or high heritability 0---------1 ENVIRONMENTAL VARIATION
Generally speaking…
· Just because a disease or trait is associated with genetic variation, this does not account for the proportion of the trait or disease that is inherited. Heritability IS NOT the same as “inherited.” Look at the example of identical twins in #1: Identical twins have the same genetic make-up; however, differences between them are associated with environmental variation. Identical twins have low heritability.
· Heritability is a correlation or association. Associating a trait or disease with genetic variability does not mean it is CAUSED by genetics. For example, look at the 1950s example with earrings. In the 1950s, men in the U.S. did not wear earrings and women did. While most men and women grew up with the same cultural expectations, the differences between those who wore earrings and those who did not were associated with genetic variation (being female XX or being male XY). The environmental variability was low and the heritability was high. But being a woman did not CAUSE the growth of earrings! And women did not pass-down earrings from one generation to the next!
The credit for this lesson goes to AP teachers Alan Feldman and Alice Kwong-Ballard. Both of these teachers presented heritability at the AP Annual Conference in 2014 – held in Philadelphia, PA.
Adapted by