Child Development

to facilitate the optimal development of children. As
children grow, the use of toys typically changes from
simple and physical (banging a block) to representa-
tional (pretending a block is a cup) to more complex
and mental (playing board games). There tend to be
gender differences in toy preferences: many girls pre-
fer relation-based toys, whereas many boys prefer ac-
tion-based toys. The influences of cultural
expectations on these preferences cannot be separat-
ed from possible biological influences. There are also
great individual differences in toy preferences re-
gardless of gender.

See also: PLAY

Bibliography
Bergen, Doris, ed. Readings from Play as a Medium for Learning and
Development. Olney, MD: Association for Childhood Educa-
tion International, 1998.
Fleming, Dan. Powerplay: Toys as Popular Culture. Manchester, Eng.:
Manchester University Press, 1997.
Goldstein, Jeffrey H., ed. Toys, Play and Child Development. Cam-
bridge, Eng.: Cambridge University Press, 1994.
Hughes, Fergus P. Children, Play, and Development. Needham
Heights, MA: Allyn and Bacon, 1998.
Steffen Saifer

TRUANCY

Truancy is defined as unexcused absences from
school without parents’ knowledge. Causes of truancy
may include social (e.g., peer pressure), family (e.g.,
low parental involvement, discord, abusive or neglect-
ful environment), and individual factors (e.g., low IQ,
drug or alcohol use, psychological disorder). As such,
frequent truancy may signal other difficulties in a
child’s life. Chronic truancy has been associated with
delinquency (e.g., daytime burglary, vandalism, run-
ning away, lying), poor academic performance, and
dropout rates. It may be predictive of criminal behav-
ior in adulthood among children who also engage in
other forms of delinquent behavior and have a history
of conduct problems from an early age. Truancy
should be distinguished from school refusal, which is
defined as staying home from school with parents’
knowledge due to emotional distress about attending.
Whereas truancy is commonly associated with antiso-
cial behavior, school refusal has been linked to anxi-
ety disorders.

See also: DELINQUENCY

Bibliography
‘‘Manual to Combat Truancy.’’ Prepared by the U.S. Department
of Education (July 1996). Available from http://www.ed.gov/
pubs/Truancy/; INTERNET.
Pamela L. Schippell

TURNER SYNDROME

Turner syndrome (genotype 45, XO) is a chromosom-

al anomaly arising from the failure of chromosomes

to separate properly during meiosis (cell division in

sex cells in which the chromosomal number is

halved). In 60 percent of the cases an egg lacking an

X chromosome (or a sperm lacking an X or Y chro-

mosome) unites with a normal sex cell to produce a

zygote, or fertilized egg, bearing a single X chromo-

some. In the remaining cases, an X chromosome is

lost from some cells during early embryonic develop-

ment, resulting in mosaics that have both normal cells

and X-deficient cells (genotype XO/XX). Mosaics in-

clude individuals with two or more distinct cell popu-

lations due to a genetic change or error soon after

conception.

Turner syndrome occurs in 1 out of 2,500 live fe-

male births, although miscarriage is the result for 99

percent of the fetuses. Clinical features, which vary

widely, include short stature, webbed neck, low-set

ears, drooping eyelids, skeletal deformities, hearing

problems, reduced secondary sexual development,

and sterility. Behavioral features include poor direc-

tional sense and poor mathematical ability. Verbal in-

telligence has been considered normal, although

studies conducted during the last decade of the twen-

tieth century suggest an increased risk for speech and

language problems. Families may be advised to seek

hormonal treatment and educational assistance for

these children.

See also: BIRTH DEFECTS; GENOTYPE

Bibliography

Plomin, Robert, John DeFries, Gerald McClearn, and Peter Mc-

Guffin. Behavioral Genetics, 4th edition. New York: Worth,

2001.

Simpson, Joe, Marion Verp, and Leo Plouffe, Jr. ‘‘Female Genital

System.’’ In Roger Stevenson, Judith Hall, and Richard Good-

man eds., Human Malformations and Related Anomalies, vol. 2.

New York: Oxford University Press, 1993.

Van Borsel, John, Inge Dhooge, Kristof Verhoye, Kristel Derde,

and Leopold Curfs. ‘‘Communication Problems in Turner

Syndrome: A Sample Survey.’’ Journal of Communication Disor-

ders 32 (1999):435–446.

Nancy L. Segal

TWIN STUDIES

Throughout history, across all cultures, people have

been fascinated with twins. In addition to interest in

the close emotional ties and biological similarities

that twins may share, reports of special twin lan-

guages and twin extrasensory perception (ESP) help

people to explore ideas of what it means to be human.

Twin language is a form of creole that some twins de-

TWIN STUDIES 419