Lifespan overheads, chapter 2: biological and environmental foundations
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Biological and Environmental Foundations
Genetic Foundations
 chromosomes: rodlike structures that store and transmit genetic
information.
 23 matching pairs, 1 from our mother and one from our father
Genetic code
 DNA - a long double-stranded molecule
 consists of pairs of chemical substances called bases, joined
together between the 2 strands. The sequence of bases
provides genetic instructions.
 a gene is a segment of DNA along the length of the
chromosome.
 Genes send instructions for making proteins
 DNA can reproduce itself through a process called mitosis
Sex cells
 a gamete contains 23 chromosomes
 meiosis: the chromosomes pair up and exchange segments so
that genes form one are replaced by genes from another.
 males can sire offspring any time after sexual maturity
 females are born with all the ova they will ever have
Male or female?
 the 23rd pair of chromosomes are sex chromosomes.
 The other 22 pairs are called autosomes.
 In females, the 23rd pair is called XX
 in males, it is XY.
 In males, X-bearing sperm and Y-bearing sperm
 In females, all gametes have an X chromosome
Multiple Births:
 Dizygotic twins
 Monozygotic twins
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Patterns of Genetic Inheritance:
 homozygous versus heterozygous
o Dominant –recessive inheritance
- E.g., hair colour (dark is dominant, blond is
recessive)
o Many diseases and disabilities are also the product of
recessive genes
- phenylketonuria (PKU)
- Cystic fibrosis
- Sickle cell anemia
- Tay-Sachs disease
o only rarely are serious diseases due to dominant genes.
An exception:
- Huntington disease - degeneration of the CNS
beginning after the age of 35
 codominance: a pattern of inheritance in which both genes
influence the person’s characteristics.
 x-linked inheritance: when a harmful gene is carried on the x
chromosome. Males are more likely to be affected because
they only have one x chromosome.
o E.g. hemophilia
 besides x-linked disorders, many sex differences reveal the
male to be at a disadvantage
o more males are miscarried
o more childhood deaths for males
o more learning disabilities, behaviour disorders, mental
retardation for boys
o possibly due to the genetic code. Females have a greater
variety of genes.
o 106 boys are born for every 100 girls born
o in recent decades the number of male births has been
declining in industrialized nations: pesticides cause
damage to/reduction in the number of Y-bearing sperm.
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 genetic imprinting: some genes get imprinted, or chemically
marked, in such a way that one member of the pair is activated
regardless of whether it is dominant or recessive.
 mutation and unfavourable genes: mutation is a sudden but
permanent change in a segment of DNA
o some occur spontaneously; others are caused by
hazardous environmental agents that enter our food
supply or are in our air
 polygenic inheritance: characteristics that vary continuously
(i.e. not either/or), like height, weight, intelligence, and
personality traits, are due to a number of genes, not just one.
Chromosomal Abnormalities
These errors involve more DNA than problems due to single genes,
so they produce disorders with many different symptoms.
 Down syndrome: the most common chromosomal disorder (1
out of every 800 live births).
o failure of the 21st pair of chromosomes to separate during
meiosis, so the new individual inherits 3 chromosomes
instead of 2.
o Mental retardation, speech problems, limited vocabulary,
slow motor development
o Short stocky build, flattened face, protruding tongue,
almond shaped eyes, unusual crease down the palm of
the hand
o Risks rise with maternal age
- 1 in 1900 births for moms who are 20
- 1 in 300 for moms who are 35
- 1 in 30 for moms whoa re 45
o in 20 to 30 percent of cases, the extra genetic material
comes from the father, not the mother
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 Abnormalities of the sex chromosomes:
XXY, XXXY= Klinefelter's syndrome, 1 in 500 male
births - male with some features of female secondary
sex characteristics (enlarged hips and breasts) at
puberty. Taller than normal XY males. Underdeveloped
testes, sterile. Some 20 to 30% are deficient in verbal
intelligence, and this is worse as the number of extra X
chromosomes increases.
XYY= Supermale syndrome, 1 in 1000 male births –
males who are taller than normal XY males, have large
teeth, often severe acne during adolescence. Typically
fertile though often with low sperm counts. IQ,
tendency to violence and aggression are, contrary to
old research, no different than in normal XY males.
X0= Turner's syndrome, 1 in 3000 female births female with stubby fingers and toes, webbed back,
broad chest and small breasts. Sterile. Normal in
verbal intelligence but often below average on
spatial abilities.
XXX, XXXX, XXX= Superfemale syndrome, 1 in
1000 female births – female, normal in appearance,
fertile. Score somewhat below average in verbal
reasoning. Delayed development in childhood
(walking, talking later than others). These delays
and intellectual deficits are worse with greater #s of
extra X's.
o fragile-X syndrome (1 in 1000 children):
The X chromosome is brittle and in some cases has
actually separated into pieces. This can lead to
mental retardation and perhaps some cases of
infantile autism. In males, about 75% with fragile-X
syndrome are retarded (mild to severe), while most
females with fragile-X syndrome are normal or have
only mild learning problems.
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Reproductive choices
 genetic counselling and prenatal diagnosis
o Amniocentesis
o Chorionic villus sampling
o Fetoscopy
o Ultrasound
o Maternal blood analysis
o Preimplantation genetic diagnosis
Environmental Contexts for Development
The family.
 learn language, skills, social, and moral values
 warm relationships predict physical/psychological health.
Isolation or alienation is associated with developmental
problems.
 Direct influences:
o When parents’ requests are accompanied by warmth and
affection, children tend to cooperate. When children
willingly comply, the parents are more likely to be warm
and gentle in the future
o When parents discipline with hostility, the children often
refuse and rebel. This misbehaviour is stressful for the
parents who may then increase their level of punishment,
leading to more unruliness.
 Indirect influences: interaction between any 2 family members
is affected by others who are also in the setting.
o can be effective supports for development
o kids can affect their parents’ relationship in powerful ways
o grandparents can promote childrens’ development in
many ways
 Adapting to change: important events create challenges that
modify existing relationships. How it works out depends on the
support provided by other family members as well as the
developmental status of the participants.
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Socioeconomic Status and family functioning
 SES is a measure of a family’s economic well-being and social
position (Years of education; Job prestige and skill; Income)
o Lower SES: marry and have kids earlier, and have more
of them
o lower SES parents place greater emphasis on external
characteristics like obedience, neatness, cleanliness,
while higher SES parents site curiosity, happiness, and
other internal characteristics.
o Lower-SES fathers focus on their role as provider and
devote less time to parenting; higher SES fathers often
share in the housework and child rearing (though rarely to
the same extent as mothers)
o Higher SES parents talk to and stimulate their infants
more and grant them greater freedom to explore. When
kids are older, they use more explanations and verbal
praise than lower SES parents, who use more criticism
and physical punishment
 Why do we find these differences?
o lower SES parents feel more powerless in their
relationships outside the home
o Education is also important.
o The greater economic security of higher SES parents
means that they don’t have to worry about making ends
meet every day, and have more time & energy for
stimulating their kids’ (and their own) intellectual and
emotional growth.
 SES is correlated with cognitive and language development
 higher SES kids do better in school; in early adulthood, they
attain higher levels of education
The impact of poverty
 over the past 30 years the poverty rate in the US has climbed.
Today 14% of the population are affected. Most vulnerable are
parents under the age of 25 with young kids, and the elderly
who live alone. It’s also worse with ethnic minorities and
women.
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o For single mothers with preschool kids and elderly black
women, the poverty rate is over 60%!
o Causes: joblessness, a high divorce rate, a lower
remarriage rate for women than for men, widowhood,
inadequate government programs
o The earlier poverty begins and the longer it lasts, the
more devastating its effects on physical and mental health
and school achievement of children.
 Homelessness: nearly 40% are families - 1 in every 4
homeless people is a child!
o Most homeless families are women with children under
age 5. These kids suffer from health problems,
developmental delays, and serious emotional stress
o 25 to 30% of homeless school-age kids don’t attend
school, and those who do achieve less well than other
poor kids, because of poor attendance and health and
emotional difficulties
Beyond the family: Neighbourhoods, towns, and cities
 in poverty-stricken urban areas, community life is usually
disrupted
o family violence and child abuse and neglect
o when family ties to the community are strong, family
stress and adjustment problems are reduced
 neighbourhoods
o affluent families are not as dependent on their immediate
surroundings for support
o also important in adulthood
o In late adulthood neighbourhoods become even more
important
 towns and cities
o small towns offer stronger connections between settings
that influence childrens’ lives.
o Adults in small towns penetrate more settings neighbours
are more willing to provide assistance
o public places are more likely to be safe and secure
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The Cultural Context
- our culture’s values have contributed to the large number of
American families who remain poor, despite working full
time
 subcultures: groups of people with beliefs and customs that differ from
those of the larger culture.
- E.g. African America families have a cultural tradition of
extended family households where 3 or more
generations live together.
Societies differ in terms of collectivism versus individualism.
 collectivist societies: people define themselves as part of a
group and stress group over individual goals.
 individualist societies: people think of themselves as separate
entities concerned with their own personal needs.
Public Policies and Lifespan Development
 public policies - laws and government programs designed to
improve current conditions
 in the US, policies protecting children and the elderly lag behind
other industrialized nations.
Policies for children, youths, and families:

In the US about 15% of children have no health insurance.

30 to 70% of 17 year olds have trouble with moderately
complex reasoning in reading, writing, math, and science

about 13% of teenagers do not graduate high school
 the American values of self-reliance and privacy have made
government reluctant to become involved in family matters, and the
public is less cohesive in support for child car and health services.
Policies for the elderly:
- of the budget for the elderly, 96% goes to social security and
medicare, at the cost of social services.
- The guaranteed minimum income people get from the
government over age 65 is below the poverty line
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The Relationship Between Heredity and the Environment
The question, “How much?”

heritability estimates
- kinship studies
 twin study
 heritability estimate: a number ranging from 0 to 1.00.

genetic factors are important in temperament and personality
(heritability indexes of .40 to .50)
 concordance rates: the percentage of instances in which both
twins show a trait when it is present in one twin.
Limitations to these measures:

heritability indexes and concordance rates may not
generalize

MZ twins reared together have more strongly correlated IQ
scores than MZ twins reared apart

when twins are separated at birth and adopted into different
homes, the households often have a lot in common

these numbers don’t tell us anything about how these traits
develop or how people might respond to environments
designed to help them develop as far as possible.
The question, “How?”
So how do heredity and environment work together to affect
development?

range of reaction (Gottesman, 1963): Because each of us
has a unique makeup, we respond differently to the same
environment.

canalization: the tendency of heredity to restrict the
development of some characteristics to just one or a few
outcomes.
Lifespan overheads, chapter 2: biological and environmental foundations
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genetic-environment correlation: our genes influence the
environments to which we are exposed.
- Passive and evocative correlation: at younger ages,
2 types of genetic-environmental correlation are
common.
(1)
passive correlation
(2)
evocative correlation
- active correlation: at older ages, active geneticenvironmental correlation becomes common (nichepicking)