In studies of human MZ and DZ twin pairs of the same sex who are ...

Question

In studies of human MZ and DZ twin pairs of the same sex who are reared together, the following concordance values are identified for various traits. Based on the values shown, describe the relative importance of genes versus the influence of environmental factors for each trait.

Trait Concordance
MZ DZ _
Blood type 100 65
Chicken pox   89 87
Bipolar disorder   67 13
Schizophrenia   72 12
Diabetes   62 15
Cleft lip   51   6
Club foot   40   4

Accepted Answer

Hi, everyone. Let's take a look at this practice problem together for various traits. Concordance values have been identified in human monozygotic and dizygotic twin pairs of the same sex raised together. What do these values indicate regarding the traits? So first, let's go ahead and review some definitions and terms for this question and then we will go through each of the answer options together. So recall that monozygotic twins are identical, so they have the same genetic makeup and dizygotic twins share only approximately 50% of the same genetic material. Now, what is Concordance recall that Concordance is used in these twin studies? And it is the probability that both individuals have the same phenotype for a specific trait. Now, concordance values can be given as a number ranging from 0 to 100% a 100% concordant value means that only genetic factors influence the phenotype. Conversely, a 0% concordance value means that no genetic factors influence the phenotype. Ok. Now that we've reviewed all that, let's go ahead and go through these answer options together. We're gonna start off with option D which states Concordance values remain the same for each trait and population being examined. Now, this answer is not a true statement. Concordance values are specific, they pertain to a specific trait within a specific population. So what we've eliminated option D option C states Concordance values provide no insight into the heritability of the traits. Now recall the definition of heritability. It is the phenotypic variation due to genetic factors. Thus, concordant values and heritability are related. Concordance gives insight into heritability. A higher concordance value indicates a higher heritability and a lower concordance value indicates a lower heritability. So we can eliminate option C as well. Option B states, similar concordance values in monozygotic and dizygotic twins indicate no influence of environmental factors on the traits. So this is also a false statement, a similar concordance value between the different twin types suggests that there is influence of environmental factors on the trait. So we've eliminated option B option A states, higher concordance values in monozygotic twins compared to dizygotic twins suggest a significant genetic contribution to the traits. Now remember that the closer the concordance is to 100% the greater the genetic factors influence the phenotype. So our correct answer is option, a higher concordance values in monozygotic twins compared to dizygotic twins suggest a significant genetic contribution to the traits. All right, everyone, I hope you found this helpful and I'll see you soon for the next practice problem

Key Concepts

Concordance Rates

Genetic vs. Environmental Influences

Twin Study Methodology

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