Biological Aspects of Development: From Fertilized Egg
to Infant
Freud said, “Biology is destiny.” Although Freud is usually thought of as a psy-
chologist, not a biologist, his early academic love was the study of biology. He
was trained as a biologist before he became a medical doctor. Freud’s statement
recognizes that, although learning and experience shape behavior, much of our
behavior is based on a foundation of genetic givens. For example, if a fertilized
egg contains an XX chromosome pattern, the individual will become a female.
If the fertilized egg contains an XY pattern, the individual will become a male.
The fact that one is a female or a male will be an important determining factor
in countless behaviors from birth to death. For a second example, let’s say that
a fertilized egg contains three chromosomes where normally there is a twenty-
first pair of chromosomes. This is a chromosomal anomaly known as trisomy
21.The individual will suffer from Down’s syndrome,a pattern characterized
by mental retardation and poor health. Freud’s view that biology is destiny has
much to recommend it. (A chromosomal anomalyis an abnormal chromo-
some pattern.)
(a) Freud said, “Biology is .”
(b) If a fertilized egg contains an XX chromosome pattern, the individual will
become a.
(c) The chromosomal anomaly known as trisomy 21 is associated with what clinical pattern
in the individual?
Answers: (a) destiny; (b) female; (c) Down’s syndrome.
The individual begins when a given sperm and a given ovum unite. Provided
by the father, the sperm,or more completely spermatozoon,is a highly mobile
cell with a tail. Provided by the mother, the ovumis a single egg cell. Both the
sperm and the ovum contain twenty-three single chromosomes. When the egg is
fertilized, there will be twenty-three pairs of chromosomes. Meiosisis the process
that reduces pairs of chromosomes to the individual chromosomes found in either
the sperm or the ovum. Mitosis,on the other hand, is the process that allows a
cell to reproduce itself. This process starts with twenty-three pairs of chromo-
somes, and all twenty-three pairs are replicated. It is mitosis that makes possible
the growth of the individual from one cell, the fertilized egg, to billions of cells.
(a) A more complete name for the sperm is the.
(b) Provided by the mother, the is a single egg cell.
Developmental Psychology: How Children Become Adults 155
