Understanding Psychology (10th Ed)

Answers to Evaluate Questions 
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When the Morrisons were expecting their second child, the young couple faced an 
anguishing dilemma. 
Their fi rst child, a girl born in 2002, had a condition known as congential adrenal 
hyperplasia, or CAH, which can sometimes result in male-like genitals in female 
newborns. So when Mrs. Morrison became pregnant again, the couple was well aware 
the baby had a 1-in-8 chance of being born with the same disorder. 
There were choices. They could treat the fetus with a powerful steroid that would 
most likely avert the possibility of the genitals becoming malformed. But the couple 
worried about doing this. There was little research on the long-term effects of treating a 
fetus with steroids, and statistically, there was a much greater chance that the baby 
wouldn’t have the genital problem at all . . . . 
The couple decided to forgo the steroid treatment. “It was touch-and-go, but in the 
end I couldn’t expose the baby to the drugs,” says Mrs. Morrison. When the baby arrived, 
it was a girl and, like her older sister, was born with swollen genitalia (Naik, 2009, p. D1). 
The Morrisons will never know if they made the right choice. But their case shows 
the diffi cult choices that parents may encounter due to our increasing understanding 
of life spent inside a mother’s womb. 
Yet, our knowledge of the biology of conception —when a male’s sperm cell pen-
etrates a female’s egg cell—and its aftermath makes the start of life no less of a 
miracle. Let’s consider how an individual is created by looking fi rst at the genetic 
endowment that a child receives at the moment of conception.
The Basics of Genetics
The one-cell entity established at conception contains 23 pairs of  chromosomes,  rod-
shaped structures that contain all basic hereditary information. One member of each 
pair is from the mother, and the other is from the father.
Each chromosome contains thousands of  genes  —smaller units through which 
genetic information is transmitted. Either individually or in combination, genes pro-
duce each person’s particular characteristics. Composed of sequences of DNA (deoxy-
ribonucleic acid) molecules, genes are the biological equivalent of “software” that 
programs the future development of all parts of the body’s hardware. Humans have 
some 25,000 different genes (see Figure 1).
Some genes control the development of systems common to all members of the 
human species—the heart, circulatory system, brain, lungs, and so forth; others shape 
the characteristics that make each human unique, such as facial confi guration, height, 
and eye color. The child’s sex is also determined by a particular combination of genes. 
Specifi cally, a child inherits an X chromosome from its mother and either an X or a 
Y chromosome from its father. When it receives an XX combination, it is a female; 
with an XY combination, it develops as a male. Male development is triggered by a 
single gene on the Y chromosome; without the presence of that specifi c gene, the 
individual will develop as a female (see Figure 2). 
As behavioral geneticists have discovered, genes are also at least partially respon-
sible for a wide variety of personal characteristics, including cognitive abilities,