Child Development From Infancy to Adolescence. Laura E. Levine
F□ The experiences you have in your life can change the structure of your genes.
Correct answers: (1) F, (2) F, (3) T, (4) F, (5) T, (6) F, (7) F, (8) T, (9) T, (10) F
Learning Questions
3.1 How has the study of genetic inheritance changed in the last century?
3.2 How do genes and chromosomes function?
3.3 How do genetic disorders develop, and what role do genetic testing and counseling play in identifying, preventing, and treating these disorders?
3.4 How do researchers study the relationship between genetic inheritance and individual traits and behavior?
3.5 How do genes and the environment interact?
Genes are the basic unit of our biological inheritance from our mother and father. In this chapter, we examine what we know about the effects of genes on children’s development. We begin with a brief historical view of the study of genetics and then describe genes and the basic ways in which they work. We then look at some types of disorders that are caused by genes and some promising ways of treating these disorders. Finally, we discuss the interaction of genes and environment to show that nature (genes) and nurture (environment) are so inextricably tied together that we cannot attribute most aspects of development separately to one or the other. As we said in Chapter 1, we have left behind the idea of nature versus nurture and have entered the era of nature through nurture.
The Study of Genes and Behavior
>> LQ 3.1 How has the study of genetic inheritance changed in the last century?
There is a long history associated with the nature versus nurture controversy based on the idea that certain human attributes will be determined by our genes (nature) or by our experiences in our environment (nurture). To begin to understand the sometimes shocking history of genetics research, read Journey of Research: The History of Research on Genetics.
Journey of Research: The History of Research on Genetics
The modern study of genetics began in 1866 when Gregor Mendel, a Central European scientist and monk, published a paper outlining a number of principles that guide the transmission of genetic information from one generation to another. These principles, which Mendel discovered by studying the way characteristics of pea plants pass from one generation to the next, came to be known as Mendelian inheritance. Although Mendel could describe the patterns of transmission, he did not know about genes and it was not until 1900 that the significance of his work was recognized (Gayon, 2016).
At about this same time, the English psychologist and anthropologist Francis Galton concluded that certain desirable traits could be bred into human beings, while undesirable ones could be bred out. This process, which Galton called eugenics, would require promoting reproduction by “superior” human beings and inhibiting reproduction by “inferior” ones. The idea was so influential that, beginning in 1907, 30 states in the United States passed laws allowing the forced sterilization of about 60,000 people considered “criminals, idiots, rapists, and imbeciles” (Watson, 2003, p. 27). (The terms idiot and imbecile in those days indicated levels of performance on IQ tests.) As the Nazis came to power in Germany in the 1930s, they enthusiastically adopted a policy that embraced eugenics. They began with sterilization but then moved to mass murder of all those they deemed unfit to reproduce for a multitude of reasons. This came to include annihilation of entire ethnic groups in the service of creating a pure “Aryan race” (Watson, 2003).
As a result of the eugenics movement and its excesses, genetics research came to be seen as suspect. It was not until the 1950s that the American biologist James Watson and British molecular biologist Francis Crick discovered the basic secrets of genetic structure and function. With their findings, scientists were able to understand the exact process that underlies the genetic transmission first described by Mendel almost 100 years earlier. In 1990, with James Watson as its first director, the Human Genome Project undertook the ambitious goal of mapping all the human genes (National Human Genome Research Institute [NHGRI], 2012a). In 2003, 50 years after Watson and Crick’s discovery, the map of the human genome was completed (NHGRI, 2016a).
Research on the human genome took another step forward in 2005 when a new technique, called genome-wide association, was developed. With this technique, instead of studying particular genes believed to be responsible for a particular disorder or trait, researchers can now study the whole genome at once to identify the relevant genes (Hu, 2013). Developments in the study of the human genome are occurring rapidly, yet much work remains to make the connections between specific genes and most human traits and behaviors (Plomin, 2013).
Genome-wide association: A technique that allows scientists to examine the whole human genome at once.
Genetics research. This scientist is using a technique that separates fragments of DNA by size and shows them on a gel sheet.
Andrew Brookes via Getty Images
Check Your Understanding
Knowledge Questions
1 What did Mendel study and how does it relate to our current understanding of genetics?
2 What did the Human Genome Project accomplish?
3 What are genome-wide association studies?
Critical Thinking
Galton believed that Mendel’s genetic principles could be used to breed better human beings. Discuss the assumptions Galton made to come to this faulty conclusion.
Molecular Genetics: Chromosomes, Genes, and DNA
>> LQ 3.2 How do genes and chromosomes function?
To begin to understand the way that genes impact child development, we begin here with a basic description of genes and how they work within a cell, a field called molecular genetics. Our genetic inheritance begins at conception. A woman’s egg cells and a man’s sperm cells each contain half of our genetic material, organized into 23 chromosomes. When a man’s sperm penetrates a woman’s egg during fertilization, the fertilized egg that results is called a zygote. When fertilization occurs, the chromosome strands from the sperm join those from the egg to form 23 matched pairs in which genes with the same function pair up. As you can see in Figure 3.1, in 22 of these pairs of chromosomes (called autosomes) the two chromosomes look very similar. However, the chromosomes in the 23rd pair can be the same or different. These chromosomes have been named the X chromosome and the Y chromosome. It is the genetic information in this 23rd pair of chromosomes that determines the gender of the conception. Women have two X chromosomes in this pair, so the eggs they produce can only contain an X chromosome in the 23rd position. Because men have an X and a Y chromosome, the sperm they produce can contain either an X or a Y chromosome in this position. When the egg and the sperm unite, it is the man’s contribution of either an X or a Y chromosome that determines the sex of the child. A conception with an X chromosome from both parents is a female. One with an X chromosome from the mother and a Y chromosome from the father is a male.
Molecular genetics: Research focused on the identification of particular genes to describe how these genes work within the cell.
Chromosomes: The strands of genes that constitute the human genetic endowment.