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### Course: MCAT>Unit 11

Lesson 3: Behavior and genetics

# Heritability

Heritability measures how much of a trait's variation in a population can be linked to genetic differences. It's not about how much a trait is genetic, but how much genetic differences account for variations. This concept is crucial in understanding intelligence, behavior, and other traits. Heritability depends on the population and environment studied. Created by Ryan Scott Patton.

## Want to join the conversation?

• if we took four genetically identical children and raised them in barrels like the Mark Twain example in the video, would they have no differences in IQ?
• Correct. Both their genetics and environment would be exactly the same. This means that their IQ would be 100% heritable, thus 100% dependent on their genome. If you want to get more complicated, their epigenomes would not necessarily be the same however (we see differences in epigenomes just from having different placentas or amniotic sacs in utero), so that could confound the example.
• Why isn't h^2 for all homozygous twin studies 0 then? Because they share 100% genes so surely all the difference is attributable to the environment?
• When the speaker says "h two" does he mean "h squared"?
h = the % variation of traits due to genes
h^2 = (the % variation of traits due to genes)^2
(1 vote)
• So taking a big stab at this:

Is h^2 (the amount of variance attributed to genetic material), similar to r^2, the statistical variable identifying how variation can be explained by a graph?

Also, can someone explain r^2 for me?

Thank you so much for your help!
(1 vote)
• Can someone also clarify what Ryan means from -?
(1 vote)
• to be sure that I have this right, are you saying, for example, that the difference in IQ between two people is 50% a result of their genetic differences (variation)?
(1 vote)

At 1.00, he said IQ is 50 percent heritable. This does not mean IQ is 50 percent genetic; difference in intelligence is 50 percent attributable to variation in genes.

When talking about variation, we are talking about the differences between individuals in a given study. So, the similarities between individuals are not accounted. For this reason, we cannot say that 50 percent of the IQ in an individual is caused by differences in genes. What we can say is that 50 percent of the variation in IQ between individuals can be explained by differences in genes.

As a result, heritability studies can only tell us the extent to which differences in genes are responsible for variation in a trait between individuals; and not how much each genes contribute to a given trait individually.

Is this line of reasoning correct or incorrect? If incorrect, can you please explain why.
(1 vote)
• If you had four quadruplets with exactly the same genome and raised them in controlled environments so that their environment was exactly the same, would they be identical?
(1 vote)
• Yes, if they all share the same genome, then they will be identical quadruplets. And since they share the same environment, there would be less variation in terms of different genes being expressed.

Also, interestingly, quadruplets can vary. You can either have all 4 babies be different from each other (i.e 4 eggs were each fertilized by a different sperm). You can have all 4 babies be identical (i.e. one egg was fertilized by a sperm, and then splits three times to form 4 embryos). And then a few other combination such as 3 identical triplets + 1 more (i.e 2 eggs were fertilized, but one of the eggs split twice to form the identical triplets). Or identical twins + 2 others (i.e 3 eggs were fertilized, and one egg was split once to get the identical twins).
(1 vote)
• Okay I understand this but , Fertal twins raised together and are close v.s. Identical twins raised apart but grow to be best friends, we see a strong commute here but they grow up not seeing eachother through the eyes that they should of , What would happen if they grow up never learning they were twins? And the children they have don't know that their close cousins.
(1 vote)
• That would be a very rare case. And, I believe you meant to type in "Fraternal or Fertile " instead of "Fertal twins". I don't really see the problem if twins grow/grew up in different places.Perhaps if you rephrased your question, I could give you a better answer. Though right now I'm confused on what you mean.