Download ch 2

Heredity, Environment, & the
Beginnings of Human Life
Biological Inheritance
Chromosomes & DNA
Each cell has a nucleus with 23 pairs of
chromosomes (46 total)
 22 pairs are matched – autosomes
 1 pair of sex chromosomes
 Chromosomes are strands of DNA
 deoxyribonucleic acid is made of 4 molecules
(bases): adenine, thymine, guanine, cytosine
 DNA self-replicates – chromosomal reproduction
allows for cell division (mitosis), which produces
2 new cells identical to original cell
Intergenerational Transmission of
Chromosomes
Germ cells – in ovaries & testes undergo a cell division
process called meiosis – each new cell contains only
23 chromosomes (1 member of each pair)
Ovum + Sperm = zygote - 1 cell with 1 nucleus with 46
chromosomes or 23 pair
Zygote begins to divide by mitosis & implants in the
lining of the uterus
This process increases hereditary diversity
Genetic Influence of Traits
DNA contains genes and intergenic material
Genes are functional units or sections of DNA – 20,00025,000 in one set of chromosomes (only accounts for
3% of the DNA material)
Genes are in matched pairs & provide a blueprint for the
production of proteins (building blocks of body)
This production occurs through a process called
transcription and is determined by regulator genes
Regulator genes are influenced by inter & intra-cellular
environment
Gene Alleles
Alleles – different varieties of a gene that represent genotype
The expression of the gene - phenotype
Alleles of the same gene can have a dominant-recessive (eye
color, curly/straight hair) relationship or a codominant
(blended or additive – e.g. AB blood type) relationship
Some traits are heavily influenced by 1 gene pair (eye color)
Most traits are affected by many different gene pairs – polygenic
trait determination
Inheritance of Gender
23rd pair of chromosomes: sex chromosome
males – XY – produce X & Y sperm
females – XX – produce X ovums
Development of male characteristics requires androgen
hormones –testosterone
Hereditary Diseases
Recessive, defective alleles:
rare – have to get both alleles for phenotype to be
expressed
e.g. sickle cell anemia – red blood cells are abnormally
shaped – results in breathing probs
We carry 3-5 recessive, defective alleles
Hereditary Diseases
Dominant defective alleles
 Only need 1 defective allele for expression
 Can happen through mutation or inheritance
Eg. Progeria, Huntington’s Chorea
Hereditary Diseases
Polygenic Disorders
run in families, but unpredictable
e.g. diabetes, MS, mental illness – 12 or more genes have
been implicated in Schizophrenia
Hereditary Diseases
Chromosomal Abnormalities
too many or too few chromosomes
either parent can be the source – increased risk with
increased age
e.g. Down Syndrome (Trisomy 21)
Hereditary Diseases
Sex-linked disorders
males are more susceptible – less viable before & after
birth
Y chromosome is smaller – males have only 1 allele for
some genes
X-linked recessive disorders – females are
carriers, males are victims
trinucleotide repeats - more likely to affect
males
Sex Chromosome # Abnormalities
 Turner’s Syndrome – genotype: XO
- appear female, but do not mature sexually
 Extra X chromosomes – genotype XXX…
developmental disabilities, reproductive probs
 Klinefelter’s syndrome – genotype: XXY - most common sex
chromosome abnormality (2/1000 male births) – cannot produce
sperm, not well developed sexual organs, may develop feminine body
shape at puberty
 XYY genotype – lined to increased rates of imprisonment – possibly
due to decreased intelligence & increase in height
Molecular Genetics
Study of what genes do & how their products influence the
body & behavior
Human Genome Project – 13 year effort to map the sequence
of chemical bases comprising all human chromosomes
(1990 – 2003)
Little is known regarding the impact of genes on complex
behaviors, but we do know that most appear to be
polygenic
Ex. Intelligence – a combination of genes & products
(proteins, enzymes) influences intelligence; however, one
missing product can cause mental retardation (ex. PKU)
Behavior Genetics
Asks: If a behavior or characteristic varies from one person to
another, how much of the difference is due to genetic
influences?
Twin & adoption studies
Heritability – the degree to which differences among
individuals on a trait may be the result of their having
different genes – when people are different, around what
percent of the variation is due to genetic differences
The degree to which identical twins differ on a trait is a
measure of the role of nonshared environment (different
envt input)
Similarities between twins that go beyond the estimates of
gentic influence can be attributed to shared envt (similar
experiences)
Area of Concern
Environmental influences may be underestimated:
 twins share a prenatal environment
 many separated twins share a portion of their lives
together (early &/or late)
 Identical twins are more likely to be dressed alike
and may be treated alike in other ways
 adoptive studies – prenatal environmental effects
could contribute to similarity to biological mother
Genetic Influences on Environment
Multidimensional models – layers & levels of
interacting causes of behavior(bidirectionality)
People play a role in shaping their own
experiences (this shaping is influenced by
genes); these experiences in-turn influence
behavior
Effects of Genes on the Environment
1.
2.
3.
Passive effects – due to parents & children’s sharing
of genes – parents’ genes affect the environment
they create for their children – environment created
is compatible with the child’s own inherited
tendencies
Evocative effects – behavior that is influenced by
genes affects the reaction of others (similar to
demand characteristics) – e.g. antisocial behavior
Active effects – people choose their own
environments (niche picking), which provide
support for & likely strengthen their choices
Coaction
 Older paradigm: Additive model of behavior
genetics, phenotype = genes + environment
 Newer paradigm: Coaction – Contributions of
genes and environment do not just add up, but
interact in complex ways. In some environments,
genes play a major role in affecting behaviors, in
other environments, the same genes have less
influence on outcomes.
 Epigenome – full set of factors (from DNA to
outside world) that controls the expression of
coded genes
 Human Epigenome project – trying to understand
the “gene-environment dance” (NIH, 2008) – p.49
Coaction & Epigenetic Model
Many interacting causal layers of functioning exist
between the physical/molecular level at which
genes operate and the level of the social
environment. Nothing exists that is purely genetic.
E.g. Rat pups stress response & mothering (p.49);
Caspi et al. (p. 50) – MAOA enzyme production
interacts with parenting environment to influence
aggressive behavior in humans; IQ & SES (P.51)
Genes impact neural activity via proteins/enzymes & neural
activity influences behavior; behavior influences the
environment & experiences; environmental influences
channel or constrain behavior, which alters neural activity
& changes genetic activity (p.51)
Genetic Interventions
Hopes for diagnosis, screening, development of
vaccines, replacement/correction of defective
genes
Somatic cell therapy – insertion of healthy genes into
appropriate tissue
Germline gene therapy – alteration of sperm or eggs to
pass-on healthy genes
Ethics?
Developmental Psychopathology: Autism
Spectrum Disorders
 Rates of autistic disorders are rising
 Co-action, nature & nurture - causes of autism is






unknown- interaction of genetic and environmental factors
Early view (1940s) autism due to poor parenting
Today conceptualized as a disorder on the spectrum of
pervasive developmental disorders
Most PDD are neurological in origin
Typically diagnosed around age 3
Social and academic performance improves when Applied
Behavioral Analysis is used for treatment
Early intervention – take advantage of the sensitive
(critical) period for developing social networks
Prenatal Development
Period of the ovum – 1st 3 weeks of pregnancy
- fertilization to implantation & development of the
neural tube (beg. of nervous system)
Period of the embryo – 4th week – 8th week
- organs systems & structures are forming in cephalocaudal and proximo-distal directions
Period of the fetus – 9th week – birth
- rapid growth & further differentiation
_
Early prenatal brain development
 Formation of the neural tube, neurulation, at 2
weeks, around 25th day the first neurons form
 Formation of major structures of the brain
 Hindbrain: medulla, pons, cerebellum, and reticular
formation, regulate autonomic functions
 Midbrain: superior colliculi, inferior colliculi, and
substantia nigra, involved in vision, hearing, and
consciousness
 Forebrain: cerebrum, thalamus, hypothalamus, and
limbic system, handles neural communication
Structure and Function of Neurons
 Neurons vary in size and shape
 A typical neuron includes
 Cell body, containing the nucleus
 Dendrites, short extensions, receive impulses
 Axon, long extension, transmits impulses
 Axon terminals, stores and releases neurotransmitters
to transmit signals across the synapse, the gap between
neurons
 Rapid neuron reproduction continues in 1st year
 Some neurons reproduce even in adulthood
 The formation of synapses is ongoing
Environmental Influences on Prenatal
Development
Teratogens – substances which produce fetal
deformities when taken or absorbed by the
mother during pregnancy
Damage is related to:
1. Stage of development
2. sensitivity/resistance
3. Dosage amount
4. Presence or absence of multiple risk factors
Alcohol
There is no safe level of alcohol consumption during
pregnancy
Fetal Alcohol Syndrome – unique facial
characteristics (small head, widely spaced eyes,
flattened nose), mental retardation, & behavioral
problems
Fetal Alcohol Effects – learning impairments
See table 2.4 for information about other teratogens
Nutrition
A shortage of protein, vitamins &/or minerals pre &
post-natally can negatively impact physical, socioemotional & intellectual devel.
Long-term impact depends in part on other risk factors
- social, educational & medical advantages help
moderate the effects of early food deprivation
Stress
Stress is unavoidable!
Eustress – positive
Distress – negative
Stress Response:
1.
Alarm phase – preparation for flight or fight
- activity of Sympathetic N.S. & adrenal glands increases
2. Resistance phase – body is moderately aroused
- parasympathetic N.S. takes over
3. Exhaustion phase – body’s resources are depleted
(depression, illness, death can occur)
The Developing Stress and
Adaptation System
 In the allostatic model, the architecture of the stress
response includes
 Central nervous system, controls multiple regulatory
processes, adjusts a variety of systems to create an
adaptive balance
 Primary stress management apparatus is the
hypothalamic-pituitary-adrenal (HPA) axis
 Sympathetic nervous system releases epinephrine and
norepinephrine, activates “fight or flight” response
 Chronic stress called allostatic load
Stress & Fetal Development
1.
2.
3.
Hormones cross the placental barrier &
contribute to shaping the developing
neuroendocrine system - influences responsivity
to stimulation, activity rhythms, ability to
modulate & regulate behavior
Heightened levels of maternal epinephrine
decrease blood flow to the uterus & placenta
If timing is on, stress hormones will interfer
with fetal testosterone production & affect
sexual orientation of male offspring
Associated problems: Hyper-reactivity to stress,
increased risk of psychopathology
Premature & Low Birth Weight
Risk factors: poverty, teratogens, insufficient
prenatal care, inadequate healthcare
Leading cause of death for neonates (1st month)
More likely to suffer from chronic medical probs,
delays in achievement of developmental
milestones, behavioral probs, feeding probs, low
IQ, academic probs
Healing touch – massage therapy
Prevention
Comprehensive in scope for high risk women
- prenatal medical care, education, counseling,
telphone contact & access to contact, postpartum visits
from nurses
Teen Pregnancy
Teen mothers:
Increased health problems
Higher rates of complications due to poor prenatal care
At risk for dropping out of school & unemployment
Children of teen mothers:
Poverty, academic failure, high rates of family violence,
unemployment, contact with criminal justice system,
teen parenthood
Programs should target multiple issues:
1. support
2. information on birth control, pregnancy & child
care
3. academic & vocational education
4. social & emotional concerns