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Biological Beginnings
Chapter 2
WHAT IS THE EVOLUTIONARY PERSPECTIVE?
 Natural Selection is the evolutionary process by which those individuals of a
species best adapted are those that survive and reproduce.
 Adaptive behavior-is behavior that promotes an organism’s survival in its habitat
(e.g., eagle’s claws, attachment in humans).
Evolutionary Psychology—Emphasizes the importance of adaptation, reproduction, and
“survival of the fittest” in explaining behavior. Evolution favors behaviors that promote
survival.
Evolutionary developmental psychology—Uses the concepts of evolutionary
psychology to understand human development. Ideas include that an extended
juvenile period in humans facilitates brain development, childhood functions
serve as preparation for adulthood and help children adapt to immediate
circumstances, evolved psychological mechanisms are domain-specific, and that
evolved mechanisms are not always adaptive in contemporary society.
Evaluating evolutionary psychology—One alternative is the bidirectional view, in
which environmental and biological conditions influence each other.
 Evolution gives bodily structures and biological potentials; does not
dictate behavior.
 Biology allows broad range of cultural possibilities.
WHAT ARE THE GENETIC FOUNDATIONS OF DEVELOPMENT?
The Collaborative Gene
The Genetic Process
Genes and chromosomes—Threadlike structures of DNA; humans have 23 pairs
and one member of each pair comes from each parent. Each gene is a short segment
composed of DNA which is a complex molecule, shaped like a double helix which
acts as a blueprint for cell reproduction. Genes are the units of heredity.
Mitosis is the process in which each chromosome in the cell’s nucleus duplicates
itself.
Meiosis is where each pair of chromosomes separates—one member going to each
gamete or the cell division to form eggs and sperm.
In the process of fertilization, a sperm fertilizes an egg to form a zygote.
Reproduction begins when female gamete (ovum) is fertilized by male gamete
(sperm). A zygote is a single cell formed through fertilization: 23 pairs of
chromosomes.
Sources of variability
 Identical twins (monozygotic twins) develop from a single zygote that
splits into two genetically identical replicas.
 Fraternal twins (dizygotic twins) develop from separate eggs and separate
sperm, making them no more similar than ordinary siblings.
 A person’s genetic heritage; the actual genetic material is the genotype
and the way an individual’s genotype is expressed in observed and
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measureable characteristics is the phenotype. Examples of observable
physical characteristics include height and eye color and psychological
characteristics such as personality and intelligence.
Genetic Principles
Dominant-recessive genes principle-In some cases, one gene of a pair always exerts
its effects; it is dominant, overriding the potential influence of the other gens called
the recessive gene. A recessive gene exerts its influence only if the two pair are both
recessive. If you inherit a recessive gene for a trait from each of your parents you
will show the trait. If you inherit a recessive gene from only one parent, you may
never know you carry the gene. Examples include hair color, eyesight, and freckles.
Sex-linked genes—When a mutated gene is carried on the X chromosome, the result
is X-linked inheritance. Since males have only one X chromosome, they are more
vulnerable to X-linked disorders such as hemophilia and fragile-X syndrome.
Genetic imprinting—When genes have differing effects depending on whether they
are inherited from the mother or the father; a chemical process “silences” one
member of the gene pair.
Polygenic inheritance—Most characteristics are determined by the interaction of
many genes. Polygenic means more than one gene. The term gene-gene interaction
is increasingly used to describe studies that focus on the interdependence of two or
more genes in influencing characteristics, behavior, diseases, and development.
Recent studies have documented gene-gene interaction in cancer and cardiovascular
disease.
Chromosome and Gene-Linked Abnormalities
Sometimes abnormalities characterize the genetic process. Some of these abnormalities
involve whole chromosomes that do not separate properly during meiosis and other
abnormalities are produced by harmful genes.
Chromosome Abnormalities
A chromosome abnormality means that the gamete (ovum or sperm) does not have a
normal set of 23 chromosomes. The most notable examples involve Down syndrome
and abnormalities of the sex chromosomes.
Down syndrome—Caused by an extra copy of chromosome 21; associated specific
physical characteristics and mental limitations. Characteristics include a round face,
a flattened skull, an extra fold of ski over the eyelids, a protruding tongue, short
limbs, and retardation of motor and mental abilities. Occurs in 1 in 700 births,
women 16-34 ok, and rarely occurs in African American children.
Sex-linked chromosomal abnormalities- Be reminded, human embryos either have
an XY or XX set of chromosomes. Human embryos must have at least one X
chromosome. The most common sex-linked chromosomal abnormalities involve the
presence of an extra chromosome (either an X or Y) or the absence of one X
chromosome in females.
Klinefelter syndrome—A sex-linked abnormality found in males who have an
extra X chromosome; affects primary and secondary sexual characteristics. A
recent study revealed significant impairment in language, academic,
attentional, and motor abilities in boys with the syndrome. Occurs 1 in 800
births.
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Fragile X syndrome—An abnormality in the X chromosome which becomes
constricted and often breaks; associated with mental retardation, learning
disabilities or a short attention span. This disorder occurs more frequently in
males than in females.
Turner syndrome—A disorder in which females are missing either an X
chromosome or part of one X chromosome; associated with possible infertility
and some learning disabilities. Females are short in stature and have a webbed
neck, may be infertile, have difficulty in math, but have verbal ability that is
high; occurs 1 in 2500 female births.
XYY syndrome—A disorder in which a male has an extra Y chromosome.
Gene-linked abnormalities—Abnormalities may be produced by not only by an uneven
number of chromosomes, but also by harmful genes.
Phenylketonuria—An individual cannot metabolize phenylalanine, an amino
acid. If left untreated, PKU can result in mental retardation and hyperactivity.
PKU accounts for about 1 percent of institutionalized individuals who are
mentally retarded, occurs primarily in non-Latino Whites. PKU is easily
detected and prevented.
Sickle-cell anemia—A genetic disorder that impairs the body’s red blood cells
so that the body’s cells do not receive enough oxygen. Most often found in
African Americans, sickle-cell anemia causes anemia and possibly early death.
Dealing with genetic abnormalities – Identifying genetic flaws could enable doctors
to predict an individual’s risks, recommend healthy practices, and prescribe safe
and effective drugs.
WHAT ARE SOME REPRODUCTIVE CHALLENGES AND CHOICES?
Prenatal Diagnostic Tests
Ultrasound sonography—A procedure in which high-frequency sound waves are
directed into the pregnant woman’s abdomen; echoes from the sounds are
transformed into visual representations of the fetus. Usually conducted around the
7th week of pregnancy and throughout pregnancy for some mothers.
Fetal MRI- MRI stands for magnetic resonance imaging and uses a powerful
magnet and radio images to generate detailed images of the body’s organs and
structure. Provides a more detailed image than ultrasound.
Chorionic villi sampling—A sample of the placenta is removed and tested for birth
defects; considered to be more dangerous than amniocentesis. Test is conducted
between 9 1/2 – 12 ½ weeks.
Amniocentesis—A test by which amniotic fluid is withdrawn and tested for
chromosomal or metabolic disorders. The later the test is done the better its
diagnostic potential, but the earlier the test is done the more useful it is in deciding
how to handle the pregnancy. Usually done within the 14-20 weeks of pregnancy.
Maternal blood screening—identifies pregnancies that have an elevated risk for
birth defects such as spina bifida and Down syndrome. Test conducted at 16-18
weeks.
Noninvasive Prenatal Diagnosis (NIPD) is increasingly being explored as an
alternative to such procedures as chorionic villi sampling and amniocentesis. The
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diagnosis focuses on isolating and examining fetal cells in the mother’s blood and
analyzes cell-free fetal DNA in maternal plasma. This test may have potential to
diagnose Down syndrome and to identify the sex of a baby as early as 5 weeks after
conception.
Infertility and Reproduction Technology
infertility, the inability to conceive a child after 12 months of intercourse without
contraception, affects approximately 10–15% of couples in the United States
Three common techniques of reproductive technology are in vitro fertilization,
(most often used) eggs and sperm are combined in a laboratory dish, and when the
egg is fertilized it is transferred into the women’s uterus; gamete intrafallopian
transfer a doctor inserts eggs and sperm directly into a woman’s fallopian tube,
and zygote intrafallopian transfer is a two-step procedure. First eggs are fertilized
in the lab, and then the fertilized eggs are transferred to a fallopian tube. 25-30%
results in multiple births.
Behavior Genetics—seeks to discover the influence of heredity and environment on
individual differences in human traits and development.
Twin study—The behavioral similarity of identical twins (monozygotic) is
compared with the behavioral similarity of fraternal twins dizygotic).
Adoption study—Investigators seek to discover whether the behavior and
psychological characteristics of adopted children are more like those of their
adoptive parents, who have provided a home environment, or more like those of
their biological parents, who have contributed their heredity.
Heredity-Environment Correlations
Passive genotype-environment correlations—Biological parents provide a rearing
environment for child. For example, children inherit tendencies from their parents
and parents also provide an environment that matches their own genetic tendencies.
Evocative genotype-environment correlations—Genetic foundations elicit social
and physical influences from the environment. (Agreeable children get more
positive attention, or a happy, outgoing child elicits smiles and friendly responses).
Active (niche-picking) genotype-environment correlations—seeking environments
that are found compatible to the individual. Libraries, sports fields, and a music
store are examples of environmental niches children might seek out if they have
intellectual interests in books, talents in sports, or musical talents.
Shared and Non-shared Environmental Experiences
Children’s common genetic inheritances versus their unique experiences in and
outside the family.
Shared environmental experiences are siblings’ common experiences
Nonshared environmental experiences are a child’s unique experiences not shared
with a sibling.
The Epigenetic View—Emphasizes that development is the result of an ongoing,
bidirectional interchange between heredity and the environment.
Conclusions about Heredity-Environment Interaction—
Heredity and environment operate together. Both environment and heredity are complex
in their own way and both are influenced by the other. Children’s development is not
only the outcome of their heredity and the environment they experience. Children also
can author a unique developmental path by changing the environment.
ECE/PSY171
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