GENOTYPE
The term ‘‘genotype’’ refers to the specific genetic
makeup of an individual and is often used with refer-
ence to allelic or mutant differences between individ-
uals at one or more genes. The genotype of an
individual is the genetic information within an indi-
vidual’s specific DNA sequence that sets the limits
upon which nongenetic parameters like environment
modulate normal and abnormal phenotypes. Geno-
types at specific genes known to cause birth defects
are used as diagnostics in genetic counseling to iden-
tify parents carrying specific disease genes and in pre-
natal genetic testing for offspring that will have birth
defects. For example, a description of a mutation
within the gene that causes cystic fibrosis is a geno-
type, while manifestation of the disease is the pheno-
type. The results of the Human Genome Project are
being used to identify DNA sequences that cause birth
defects. The genotypes associated with birth defects
are then available for development of more accurate
diagnostic tests.
See also: GENETIC COUNSELING; HUMAN GENOME
PROJECT
Bibliography
Oak Ridge National Laboratory. ‘‘The Science behind the Human
Genome Project.’’ Available from http://www.ornl.gov/hgmis/
project/info.html; INTERNET
David W. Threadgill
Robert E. Boykin
GESELL, ARNOLD (1880–1961)
Prior to the early twentieth century, scientific observa-
tions of children were not common. Arnold Gesell was
one of the first psychologists to systematically de-
scribe children’s physical, social, and emotional
achievements, particularly in the first five years of life.
In fact, the developmental norms established by Ge-
sell and his colleagues are still used by pediatricians
and psychologists today.
Gesell was born and raised in Alma, Wisconsin,
and received a doctorate in psychology in 1906 from
Clark University. In 1911 he began a faculty position
in education at Yale University. While fulfilling the
requirements of his teaching and research position,
he also worked toward a doctorate in medicine, which
he earned in 1915. While at Yale, Gesell established
and directed the Clinic of Child Development, where
children’s achievements in terms of physical and psy-
chological development were observed and mea-
sured. Gesell’s observations of children allowed him
to describe developmental milestones in ten major
areas: motor characteristics, personal hygiene, emo-
Arnold Gesell was one of the first psychologists to systematically
describe children’s achievements in terms of physical and
psychological development. (UPI/Corbis-Bettmann)tional expression, fears and dreams, self and sex, in-
terpersonal relations, play and pastimes, school life,
ethical sense, and philosophic outlook. His training
in physiology and his focus on developmental mile-
stones led Gesell to be a strong proponent of the
‘‘maturational’’ perspective of child development.
That is, he believed that child development occurs ac-
cording to a predetermined, naturally unfolding plan
of growth.
Gesell’s most notable achievement was his contri-
bution to the ‘‘normative’’ approach to studying chil-
dren. In this approach, psychologists observed large
numbers of children of various ages and determined
the typical age, or ‘‘norms,’’ for which most children
achieved various developmental milestones.
When Gesell retired from Yale in 1948, his col-
leagues established a private institution in his name
in New Haven, Connecticut, called the Gesell Insti-
tute of Child Development. During the 1970s and
1980s Gesell’s research prompted many books and
articles to be published by researchers associated with
the institute. These writings became popular with
parents and teachers because they described the typi-
cal behaviors to be expected of children at each age;
however, Gesell’s writings have been criticized by166 GENOTYPE