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Chapter 23: Problem 10

Describe the value of using twins in the study of questions relating to the relative impact of heredity versus environment.

Short Answer

Expert verified
Answer: Twins are often used in such studies because they allow researchers to differentiate between the roles of heredity and environment in specific traits, as they share varying degrees of genetic information and often have similar early-life environments. Comparing and contrasting different types of twins (monozygotic and dizygotic) in various environmental conditions helps researchers disentangle the relative contributions of heredity and environment, ultimately deepening our understanding of human development and behavior.

Step by step solution

01

Introduction to Heredity and Environment

Heredity deals with the influence of genes on a person's traits, whereas environment refers to all external factors, such as upbringing and experiences, that can affect a person's development and behavior. Researchers have long been interested in understanding the relative importance of these two factors in determining human characteristics, including personality, intelligence, and susceptibility to certain diseases.
02

Types of Twins and Their Significance

Twins can be classified into two types: monozygotic (identical) twins and dizygotic (fraternal) twins. Monozygotic twins come from a single fertilized egg that splits into two, resulting in genetically identical individuals with almost 100% shared genes. Dizygotic twins, on the other hand, come from two separate fertilized eggs, making them genetically similar to regular siblings, sharing about 50% of their genes. The study of twins is valuable because it allows researchers to differentiate between the roles of heredity and environment in specific traits since twins often share the same environment in early life.
03

Monozygotic Twins in Heredity vs. Environment Studies

Monozygotic twins are especially valuable in studies of heredity and environment because of their identical genetic makeup. If identical twins raised together have similar outcomes or traits, it suggests that heredity plays a significant role in these traits. To further isolate the effects of the environment, researchers may also study identical twins who were separated at birth – known as twin-adoption studies. If identical twins raised in different environments still display strong similarities, it is evidence that heredity has a more significant influence on those traits.
04

Twin Studies and the Role of Shared Environment

By comparing monozygotic and dizygotic twins raised together or apart, researchers can also determine the role of shared environment in shaping traits. If dizygotic twins raised together exhibit strong similarities, it indicates that shared environment plays an essential role in those traits. Conversely, if monozygotic twins raised apart are not as similar as those raised together, it also points to the influence of the shared environment during the development of traits.
05

Conclusion

In summary, twins are a valuable resource for researchers studying the effects of heredity and environment on human traits and behaviors since they share varying degrees of genetic information and, often, similar environments. By comparing and contrasting different types of twins in various environmental conditions, researchers can disentangle the relative contributions of heredity and environment to traits and deepen our understanding of human development and behavior.

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Most popular questions from this chapter

Height in humans depends on the additive action of genes. Assume that this trait is controlled by the four loci \(\mathrm{R}, \mathrm{S}, \mathrm{T}\) and \(\mathrm{U}\) and that environmental effects are negligible. Instead of additive versus nonadditive alleles, assume that additive and partially additive alleles exist. Additive alleles contribute two units, and partially additive alleles contribute one unit to height. (a) Can two individuals of moderate height produce offspring that are much taller or shorter than either parent? If so, how? (b) If an individual with the minimum height specified by these genes marries an individual of intermediate or moderate height, will any of their children be taller than the tall parent? Why or why not?

The mean and variance of plant height of two highly inbred strains \(\left(P_{1} \text { and } P_{2}\right)\) and their progeny \(\left(F_{1} \text { and } F_{2}\right)\) are shown here. $$\begin{array}{ccc}\text { Strain } & \text { Mean (cm) } & \text { Variance } \\\\\mathrm{P}_{1} & 34.2 & 4.2 \\\\\mathrm{P}_{2} & 55.3 & 3.8 \\\\\mathrm{F}_{1} & 44.2 & 5.6 \\\\\mathrm{F}_{2} & 46.3 & 10.3\end{array}$$ Calculate the broad-sense heritability \(\left(H^{2}\right)\) of plant height in this species.

Many traits of economic or medical significance are determined by quantitative trait loci (QTLs) in which many genes, usually scattered throughout the genome, contribute to expression. (a) What general procedures are used to identify such loci? (b) What is meant by the term cosegregate in the context of QTL mapping? Why are markers such as RFLPs, SNPs, and microsatellites often used in QTL mapping?

The following variances were calculated for two traits in a herd of hogs. $$\begin{array}{lccc}\text { Trait } & V_{P} & V_{C} & V_{A} \\\\\text { Back fat } & 30.6 & 12.2 & 8.44 \\\\\text { Body length } & 52.4 & 26.4 & 11.70\end{array}$$ (a) Calculate broad-sense \(\left(H^{2}\right)\) and narrow-sense \(\left(h^{2}\right)\) herita bilities for each trait in this herd. (b) Which of the two traits will respond best to selection by a breeder? Why?

Erma and Harvey were a compatible barnyard pair, but a curious sight. Harvey's tail was only \(6 \mathrm{cm}\) long, while Erma's was \(30 \mathrm{cm} .\) Their \(\mathrm{F}_{1}\) piglet offspring all grew tails that were \(18 \mathrm{cm}\) When inbred, an \(\mathrm{F}_{2}\) generation resulted in many piglets (Erma and Harvey's grandpigs), whose tails ranged in \(4-\mathrm{cm}\) intervals from 6 to \(30 \mathrm{cm}(6,10,14,18,22,26, \text { and } 30) .\) Most had \(18-\mathrm{cm}\) tails, while \(1 / 64\) had \(6-\mathrm{cm}\) tails and \(1 / 64\) had \(30-\mathrm{cm}\) tails. (a) Explain how these tail lengths were inherited by describing the mode of inheritance, indicating how many gene pairs were at work, and designating the genotypes of Harvey, Erma, and their 18 -cm-tail offspring. (b) If one of the \(18-\mathrm{cm} \mathrm{F}_{1}\) pigs is mated with one of the \(6-\mathrm{cm}\) \(\mathrm{F}_{2}\) pigs, what phenotypic ratio will be predicted if many offspring resulted? Diagram the cross.
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