Infants and Children in Context. Tara L. Kuther

blood (Warsof, Larion, & Abuhamad, 2015). Testing can be done after 10 weeks, typically between 10 and 22 weeks. Given that the test involves drawing blood from the mother, there is no risk to the fetus. The use of NIPT has increased dramatically in the United States and other countries (Hui, Angelotta, & Fisher, 2017). However, NIPT cannot detect as many chromosomal abnormalities as amniocentesis or CVS and does so with less accuracy (Chan et al., 2013; National Coalition for Health Professional Education in Genetics, 2012). Researchers have identified the entire genome sequence using NIPT, suggesting that someday, NIPT may be as effective as other, more invasive techniques (Tabor et al., 2012). Pregnant women and their partners, in consultation with their obstetrician, should carefully weigh the risks and benefits of any procedure designed to monitor prenatal development.

      Prenatal Treatment of Genetic Disorders

      What happens when a genetic or chromosomal abnormality is found? Advances in genetics and in medicine have led to therapies that can be administered prenatally to reduce the effects of many genetic abnormalities. Fetoscopy is a technique that uses a small camera, inserted through a small incision on the mother’s abdomen or cervix and placed into the amniotic sac that encases the fetus, to examine and perform procedures on the fetus during pregnancy. Risks of fetoscopy include infection, rupture of the amniotic sac, premature labor, and fetal death. However, when serious abnormalities are suspected, fetoscopy permits a visual assessment of the fetus, which aids in diagnosis and treatment. Hormones and other drugs, as well as blood transfusions, can be given to the fetus by inserting a needle into the uterus (Fox & Saade, 2012; Lindenburg, van Kamp, & Oepkes, 2014). Surgeons rely on the images provided by fetoscopy to surgically repair defects of the heart, lung, urinary tract, and other areas (Deprest et al., 2010; P. Sala et al., 2014).

      In addition, researchers believe that one day, we may be able to treat many heritable disorders thorough genetic engineering by synthesizing normal genes to replace defective ones. It may someday be possible to sample cells from an embryo, detect harmful genes and replace them with healthy ones, and then return the healthy cells to the embryo where they reproduce and correct the genetic defect (Coutelle & Waddington, 2012). This approach has been used to correct certain heritable disorders in animals and holds promise for treating humans.

      Thinking in Context 2.3

      1 Provide advice to Eduardo and Natia, a couple in their mid-30s who are seeking reproductive assistance. What are their options and what are the advantages and disadvantages of each?

      2 Suppose that you are a health care provider tasked with explaining prenatal diagnostic choices to a 38-year-old woman pregnant with her first child. How would you explain the tests? What would you advise? Why?

      Heredity and Environment

      Our brief introduction to the processes of heredity illustrates the complexity of genetic inheritance. In fact, most human traits are influenced by a combination of genes (polygenic) working in concert with environmental influences. Our genotype, or genetic makeup, inherited from our biological parents is a biological contributor to all of our traits, from hair and eye color to personality, health, and behavior. However, our phenotype, the traits we ultimately show, such as our specific eye or hair color, is not determined by genotype, our genetic blueprint, alone. Phenotypes result from the interaction of genotypes and our experiences.

      Behavioral Genetics

      Behavioral genetics is the field of study that examines how genes and experience combine to influence the diversity of human traits, abilities, and behaviors (Krüger, Korsten, & Hoffman, 2017; Plomin et al., 2013). Behavioral geneticists have discovered that even traits with a strong genetic component, such as height, are modified by environmental influences (Dubois et al., 2012; Plomin, DeFries, Knopik, & Neiderhiser, 2016). Moreover, most human traits, such as intelligence, are influenced by multiple genes, and there are often multiple variants of each gene and each might interact with the environment in a different way (Bouchard, 2014; Chabris, Lee, Cesarini, Benjamin, & Laibson, 2015; Knopik, Neiderhiser, DeFries, & Plomin, 2017).

      Methods of Behavioral Genetics

      Behavioral geneticists seek to estimate the heritability of specific traits and behaviors. Heritability refers to the extent to which variation among people on a given characteristic is due to genetic differences. The remaining variation not due to genetic differences is instead a result of the environment and experiences. Heritability research therefore examines the contributions of the genotype but also provides information on the role of experience in determining phenotypes (Plomin et al., 2016). Behavioral geneticists assess the hereditary contributions to behavior by conducting selective breeding and family studies.

      Selective breeding studies entail deliberately modifying the genetic makeup of animals to examine the influence of heredity on attributes and behavior. For example, mice can be bred to be very physically active or sedentary by mating highly active mice only with other highly active mice and, similarly, by breeding mice with very low levels of activity with each other. Over subsequent generations, mice bred for high levels of activity become many times more active than those bred for low levels of activity (Knopik et al., 2017). Selective breeding in rats, mice, and other animals such as chickens has revealed genetic contributions to many traits and characteristics, such as aggressiveness, emotionality, sex drive, and even maze learning (Plomin et al., 2016).

      For many reasons, especially ethical reasons, people cannot be selectively bred. However, we can observe people who naturally vary in shared genes and environment. Behavioral geneticists conduct family studies to compare people who live together and share varying degrees of relatedness. Two kinds of family studies are common: twin studies and adoption studies (Koenen, Amstadter, & Nugent, 2012). Twin studies compare identical and fraternal twins to estimate how much of a trait or behavior is attributable to genes. Recall that identical (monozygotic) twins share 100% of their genes because they originated from the same zygote. Like all nontwin siblings, fraternal (dizygotic) twins share 50% of their genes, as they resulted from two different fertilized ova and from two genetically different zygotes. If genes affect a given attribute, identical twins should be more similar than fraternal twins because identical twins share 100% of their genes, whereas fraternal twins share about half.

      Adoption studies, on the other hand, compare the degree of similarity between adopted children and their biological parents whose genes they share (50%) and their adoptive parents with whom they share an environment but not genes. If the adopted children share similarities with their biological parents, even though they were not raised by them, it suggests that the similarities are genetic. The similarities are influenced by the environment if the children are more similar to their adoptive parents. Observations of adoptive siblings also shed light on the extent to which attributes and behaviors are influenced by the environment. For example, the degree to which two genetically unrelated adopted children reared together are similar speaks to the role of environment. Comparisons of identical twins reared in the same home with those reared in different environments can also illustrate environmental contributions to phenotypes. If identical twins reared together are more similar than those reared apart, an environmental influence can be inferred.

      Genetic Influences on Personal Characteristics

      Research examining the contribution of genotype and environment to intellectual abilities has found a moderate role for heredity. Twin studies have shown that identical twins consistently have more highly correlated scores than do fraternal twins. For example, a classic study of intelligence in over 10,000 twin pairs showed a correlation of .86 for identical and .60 for fraternal twins (Plomin & Spinath, 2004). Table 2.7 summarizes the results of comparisons of intelligence scores from individuals who share different genetic relationships with each other. Note that correlations for all levels of kin are higher when they are reared together, supporting the role of environment. Average correlations also rise with increases in shared genes.

      Table 2.7