Download PSYC 2314 Chapter 3

PSYC 2314
Lifespan Development
Chapter 3
Heredity and Environment
Development Begins
• Conception occurs when the male gamete (sperm)
penetrates the membrane of the female gamete
(the ovum); the gametes then fuse, and their
genetic material combines, to form the one-celled
zygote.
• Within hours, the zygote initiates the human
development through the processes of duplication
and division. Soon after, differentiation begins.
Each body cell created from these processes
carries an exact copy of the zygote’s genetic
instructions.
Development Begins
• Instructions on each gene that specify the
form, location, and function of each body
cell are “written” in a chemical code made
up of four bases:
–
–
–
–
Adenine
Guanine
Cytosine
Thymine
Development Begins
• The 23rd pair of chromosomes, which
determines sex, is designated XY in the
male and XX in the female. The critical
factor in the determination of the zygote’s
sex is which sperm reaches the ovum first, a
Y sperm, creating a boy, or an X sperm,
creating a girl.
Development Begins
• Genes accomplish two goals that are
essential to our survival:
– Ensure genetic continuity across the species
– Ensure genetic diversity within it
Development Begins
• Age-related changes in the sex ratio
– Worldwide, slightly more males than females
are born each year.
– Because males have a slightly higher rate of
childhood death, a balance occurs at about 25.
– After age 50, the sex ratio favors women.
Development Begins
• Monozygotic Twins
– A single zygote splits into two separate
identical cells that develop into genetically
identical, who have the potential for developing
the same physical appearance and
psychological characteristics and the same
vulnerability to specific diseases.
Development Begins
• Dizygotic Twins
– Begin life as two separate zygotes and share no
more genes than any other siblings.
Genotype to Phenotype
• Polygenetic: affected by many genes
• Multifactorial: influenced by many factors,
including environmental
• Genotype: the sum total of all the genes a
person inherits
• Phenotype: the sum total of all the genes
that are actually expressed
Genotype to Phenotype
• Additive gene: when genes interact
additively, the phenotype reflects the
contributions of all the genes that are
involved.
• Dominant gene: the stronger of an
interacting pair of genes.
• Recessive gene: the weaker of an
interacting pair of genes.
Genotype to Phenotype
• X-linked Genes: genes that are on the X
chromosome.
– If an X-linked gene is recessive—as are the
genes for most forms of color-blindness, many
allergies, several diseases, and some learning
disabilities—the fact that it is on the X
chromosome is critical.
Genotype to Phenotype
• Genetic Imprinting
– Certain genes tend to be expressed differently
when they are inherited from the mother than
when they are inherited from the father.
– Some of the genes that influence height, insulin
production, and several forms of mental
retardation affect a child in different ways—
even in opposite ways—depending on which
parent they came from.
Genotype to Phenotype
• Effects of genes and environment on development
– Research has revealed that most behavioral traits are
affected by the interaction of large number of genes
with environmental factors.
– Genes are part of a person’s basic foundation, affecting
many aspects of life while determining none.
– Even traits that show a strong genetic influence are also
affected by environment.
Environmental Influences on
Emotional Impairment
• The following psychological traits have
strong genetic influences, but they are also
affected by the social atmosphere:
–
–
–
–
–
Shyness (inhibition)
Intelligence
Emotionality
Activity level
Aggression
Environmental Influences of
Mental Disorders
• Both genes and environment are influential
in determining psychopathologies:
–
–
–
–
–
Depression
Phobias
Antisocial behavior
Schizophrenia
Alcoholism
Inherited Abnormalities
• Major Methods of Prenatal Diagnosis:
– Pre-implantation Testing
– Alphafetoprotein Assay
– Ultrasound
Inherited Abnormalities
• Prenatal Testing:
– Fetoscopy
– Amniocentesis
– Chorionic Villi Sampling
Chromosomal Miscount
• Down Syndrome (Trisomy-21)
– Individual has 3 chromosomes at site 21
– Specific facial characteristics: round face, thick
tongue, unusual eyes.
– Also, heart abnormalities, hearing problems,
muscle weakness, mental retardation, and short
stature
Chromosomal Miscount
• Abnormalities at the 23rd location
– At the 23rd pair, either missing a X chromosome
or has two or more other sex chromosomes in
addition to the first X.
– Impair cognitive and psychosocial development
and sexual maturation
Chromosomal Discount
• The Fragile X
– A disorder in which part of the X chromosome
is attached to the rest of it by a very slim string
of molecules.
– Mental deficiency
– Inadequate social skills and extreme shyness
Harmful Genes
• Huntington’s Chorea
– A central nervous system disease caused by a gene that
remains inactive until adulthood, by which time a
person could have had many children.
• Tourette Syndrome
– Exhibit recurrent uncontrollable tics and explosive
outbursts of verbal obscenities (30%). An occasional
twitch and a postponal impulse to speak inappropriately
(70%).
Genetic Counseling
• Situations in which couples should seek
genetic testing and counseling:
– Individuals who have a parent, sibling, or child
with serious genetic condition.
– Couples who have a history of early
spontaneous abortions, stillbirths, or infertility.
Genetic Counseling
• Situations in which couples should seek
genetic testing and counseling:
– Couples who are from the same ethnic group or
subgroup—especially if the group is a small
one or most particularly if the couple are close
relatives.
– Women over age 34.