Understanding Psychology (10th Ed)

chromosomes
Rod-shaped structures 
that contain all basic hereditary 
information.
genes
The parts of the chromosomes 
through which genetic information is 
transmitted.
 Key Concepts 
What is the nature of 
development before birth? 
What factors aff ect a child 
during the mother’s 
pregnancy?
M O D U L E 3 6
Prenatal Development: 
Conception to Birth
Study Alert
It’s important to understand 
the basic building-blocks of 
genetics: chromosomes, 
which contain genes, 
which in turn are com-
posed of sequences of DNA.
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 Module 
36 
Prenatal Development: Conception to Birth 
387
personality traits, and psychological disorders. Of course, few of these characteristics 
are determined by a single gene. Instead, most traits result from a combination of 
multiple genes that operate together with environmental infl uences (Plomin & 
McGuffi n, 2003; Haberstick et al., 2005; Ramus, 2006).
THE HUMAN GENOME PROJECT 
Our understanding of genetics took a giant leap forward in 2001, when scientists 
were able to map the specifi c location and sequence of every human gene as part 
of the massive Human Genome Project . The accomplishment was one of the most 
FIGURE 1
Every individual’s characteristics are determined by the individual’s specifi c genetic 
information. (a) At the moment of conception, (b) humans receive 23 pairs of chromosomes, 
half from the mother and half from the father. (c) These chromosomes are made up of coils 
of DNA. (d) Each chromosome contains thousands of genes that “program” the future 
development of the body.