Chapter 16, Problem 1RQ

Summary Introduction

Introduction: Genetic epidemiology is a part of epidemiology that aims to understand the contribution of host genetics or genetic factors to complex disease and quantitative phenotypes, and also to identify their relative importance. There are some difference among every human being in terms of physical characteristics, personality, and other factors. However, most of the human diseases are controlled by some combination genetic and environmental factor acting together.

Answer to Problem 1RQ

Correct answer: “If a greater proportion of monozygotic twin pairs are found to be concordant for a certain disease than are dizygotic twin pair, the observation suggests that the disease is most likely caused by hereditary factors almost exclusively, with some nonhereditary factors possibly playing a role”. Hence, option c. is the correct answer.

Explanation of Solution

Reason for the correct answer:

The twins are the two young ones produced from the same single pregnancy. In the case of identical twins, the zygote develops from single zygote (monozygotic). The “monozygotic twins” are formed from one fertilized ova. After the conception the zygote further divides into 2 parts, which resulted in the development and formation of the 2 different individual embryos.

In the given statement, it is given that the monozygotic twins are concordant for a certain diseases than the dizygotic twin pair. In such way, it suggests that genetics play an important role because the twins have identical genetic material in case of monozygotic twin. Along with this, it is often seen that identical twins are raised in similar manner, exposed to similar environmental condition.

Therefore, the observation suggests that the occurred disease is most likely exclusively caused by hereditary factors, along with some nonhereditary factors possibly playing a role.

Option c. is given as “Hereditary factors almost exclusively, with some nonhereditary factors possibly playing a role”. The heredity or genetic factors exclusively with some nonheredity or environmental factors possible play an important role in case of identical twins concordant for a disease.

Hence the correct answer is option c.

Reasons for incorrect answers:

Option a. is given as, “Exclusively environmental factors”. The heredity factors exclusively with some nonheredity possibly play an important role for monozygotic twins who are concordant for a disease, not only exclusively environmental factors.

Hence, option a. is incorrect.

Option b. is given as, “Exclusively genetic factors”. The heredity factors exclusively with some nonheredity possibly play an important role for monozygotic twins who are concordant for a disease, not only exclusively genetic factors.

Hence, option b. is incorrect.

Option d. is given as, “Environmental and genetic factors almost equally”. This is incorrect because the heredity factors exclusively with some nonheredity possibly play an important role for monozygotic twins who are concordant for a disease.

Hence, option d. is incorrect.

Option e. is given as, “Gender differences in monozygotic twins”. The heredity factors exclusively with some nonheredity possibly play an important role for monozygotic twins, who are concordant for a disease, not gender differences in monozygotic twins.

Hence, option e. is incorrect.

Hence the options a., b, d., and e. are incorrect.

Conclusion

In case of identical twins, the heredity or genetic factors exclusively with some nonheredity or environmental factors possible play an important role.