Hereditary Influences on Development
Principles of hereditary transmission
Genotype (one’s genetic heritage) vs.
phenotype (what is expressed, visible to observe)
Conception- the moment the egg is fertilized by
the sperm. The entire genetic code is present.
Zygote-single cell formed at conception
Chromosomes-46 in nucleus of each cell, made
up of genes
DNA-deoxyribonucleic acid-double-stranded
molecules that make up chromosomes, double-helix
Mitosis-cell duplication by duplicating
chromosomes and dividing into identical cells.
Meiosis-process of division of sex cellsproduces gametes with half the parent’s
chromosomes.
Multiple births can occur in two ways:
Monozygotic (identical) twins-a single zygote
splits and produces twins with identical DNA 1/250
Dizygotic (fraternal) twins-two ova are
fertilized, producing different DNA when fertilized
by 2 sperm 1/125
Gender determination-the 23rd pair of chromosomes
determines sex. XX is female, XY is male A
karyotype is a picture of the chromosomes.
Functions of the genes
 Produce amino acids necessary for the
formation & function of new cells
 Regulate the pace of development
 Even so, environmental factors influence
how messages from the genes are carried out
Dominant-recessive inheritance is produced by
alleles (different forms of a gene that can appear on a
chromosome) and the combination of alleles. Simple
inheritance requires only one genetic pair.
Dominant allele-more powerful gene that is
expressed in the phenotype
Recessive allele-less powerful gene that us not
expressed unless paired with another recessive allele.
Carrier-person who displays no sign of a
recessive trait in his phenotype, but carries the
recessive allele and can pass the trait on to child.
Codominant-2 equally powerful alleles can
compete for dominance and both be expressed. (AB
blood type has allele for both A and B, with equal
portions of A- and B-antigens. Sickle cell anemia
can be carried recessively, but it affects blood cells to
some extent, not producing severe signs of disease.
Sex-linked characteristic-traits that are
determined by genes on the sex chromosomes,
mostly on the X, so they affect males more intensely
(since they only have one X) Color-blindness 8/100M
Genetic imprinting-a pattern of inheritance in
which only one parent’s gene is expressed, regardless
of whether it is dominant or recessive.
Polygenic traits -one trait that is created by the
action of several genes, not simply one. Height,
weight, IQ, skin color, temperament, risk of cancer.
Abnormalities
Congenital defects- defects present at birth even
if they aren’t noticeable. (Huntingdon’s disease is
present at birth but doesn’t begin the CNS
deterioration until later in life.)
Chromosomal Abnormalities-if during the
meiotic reproduction of alleles the distribution of
chromosomes is uneven, it’s usually fatal and results
in abortion of the fetus. Some simply produce odd
characteristics: Turner’s syndrome XO, Superfemale
XXX, Kinefelter’s syndrome XXY, Supermale XYY
Fragile-X syndrome-one X has broken off,
causes mental retardation, infantile autism, sterility
Down syndrome-is caused by trisomy 21,
where the 21st chromosome has extra chromosomal
material or not enough. Facial features are common,
mild to serious mental retardation, heart and sensor
(ear, eye) defects.
Aging-ova hypothesis-one hypothesis for
chromosomal abnormalities- aging mothers have
aging eggs with deteriorate. Also some mothers don’t
metabolize folic acid well and puts baby at risk.
Genetic Abnormalities-can result as a result of
mutations- spontaneous changes in the structure of a
gene that produces a new phenotype.
Recessive hereditary defects occur when
both parents carry a recessive gene for a disease and
the child inherits both. Sickle cell anemia. CF, PKU,
hemophilia, Tay-Sachs disease.
Genetic Counseling serves to help parents know the
risk of delivering a child with abnormalities due to
inheritance. It is particularly encouraged if the couple
has already delivered a child with abnormalities.
Prenatal Detection of abnormalities
Amniocentesis- extracting amniotic fluid with
fetal cells that can be tested for abnormalities. May
be done after 11-14 wks gestation.
Chorionic villus sampling (CVS)- take fetal
cells from the chorion for testing. Can be done 8-9
weeks gestation. Has a greater risk of miscarriage.
Ultrasound-scanning the womb externally with
sound waves to produce a visual of fetus. Helpful for
detecting gross abnormalities, multiple babies.
Treating hereditary disorders-with many severe
disorders, there is no treatment, but the parents have
the option of abortion.
PKU- phenylketonuria-disease where baby
can’t metabolize phenylanaine, a protein which
builds up in toxicity and produces mental retardation.
All babies are tested at birth. Those with it must stay
on a special diet, in which no toxins are produced.
Intrautero fetal surgery-can repair some heart,
neural tube, urinary tract or lungs can be corrected.
Gene replacement therapy-CF-cystic fibrosisthe CF gene has been pinpointed and can be
neutralized. Gene replacement therapy inserts normal
genes to replace the defective gene.
Germline gene therapy-potential therapy where
harmful genes are altered or replaced with healthy
ones in the embryonic stage. Still not OKed for
humans.
Ethical issues –
Fetal surgery can induce miscarriage &
problems from complications.
Gene replacement therapy-benefits outweigh
the risks for children with severe illnesses.
Germline gene therapy this could alter
genotypes for future generations (positive eugenics)
which brings the question- Who decides what is a
positive enhancement of the human race? Do we start
rejecting more and more borderline functioning
people because they are inconvenient? Even today in
vitro fertilization techniques allow parents to
choose the gender of their babies. Sonograms in
China have changed the rates of boys/girls there. The
results of negative eugenics were seen in Nazi
Germany as they attempted to eliminate all the
“undesirables”. In this country we have allowed legal
sterilization of mentally retarded adults with little
legal rights under the law.
Methods of study of hereditary influences
Behavioral genetics- study of how genotype
interacts with environment to produce personal
attributes such as IQ, personality, disorders.
Heritability studies seek to determine the
heritability of various traits. How much a trait is
determined by heredity or environment.
Selective breeding studies track breeding of
animals to try to develop certain traits.
Family kinship studies-examining traits
according to how genetically similar members are
who carry it.
Twin design-comparing twins reared
together to fraternal twins on a specific trait.
Adoption design-compares adoptees to
genetically unrelated people in the family.
Concordance rates-comparing percentages of
one twin with a trait to the other twin. (If a trait is
found in both twins all the time, it is 100%
concordant. If it is present half the time, it is 50%)
Heritability coefficient-the estimate of variation
in a attribute that is attributable to heredity. IQ is .52
heritable (meaning over half the trait can be linked to
genetics)
Nonshared environmental influencesenvironment that people living together don’t share
that contributes to differences in family members.
Activities, friends, treatment by parents. Parents,
especially dads treat boys differently from girls. It
contributes a lot to personality differences. Siblings
treat one another differently depending on birth
order.
Shared environmental influences-experiences
the family members share that contribute to similarity
Misconceptions about heritability-estimates
only apply to populations, not individuals. They
differ with different environmental influences. They
are subject to modification by environment.
Inheritance is not unchangeable.
 Hereditary influences on IQ-Genetic influences
appear more obviously the older the child grows.
The influence of shared environment declines
with age.
 Hereditary influences on personality-while
overall the hereditary influence on personality is
more subtle than in IQ, some traits are highly
heritable.
Introversion/extroversion-similar level of
heritability as IQ, since this has to do with
physiological responses to novel stimuli.
Empathy-measure of how much a person
recognizes and responds to the needs of others. This
is noticeable soon after birth in nursery – how much
some children respond to others’ crying.
 Hereditary influences on Mental disordersSchizophrenia-genetic connection from parent
shown in concordance rates of identical twins
compared to fraternal twins (.48 Id, .17 frat)
Manic-depression-mood disorders show high
levels of heritability
Neurotic disorders-brain response is
heightened, more stimuli are considered threats.
There is a predisposition to develop illness, not a
mandate. Environment does figure in here.
Canalization principle-restriction of phenotype to
only a few outcomes- the more canalized a trait is,
the more predetermined the outcome, so environment
has less possible effect. Babbling in infancy is
common to all babies, even deaf ones.
Range-of-Reaction Principle- genotype restricts the
range of possible manifestations- variety is possible.
 Passive genotype/environment correlationsrearing environments of a child are influenced by
the parents’ genes. More empathic or athletic
parents will set up opportunities to display and
reward those behaviors in child, triggering their
inheritance.
 Evocative genotype/environment correlationsour genetic dispositions affect the people who
raise us and influence our social environment.
Temperament really figures in here.
 Active genotype/environment correlations-our
genetic predispositions will lead us to seek
environments that fit us, enhancing those traits.
Goodness of fit makes a difference here – the better
the child’s traits match the parents, the better
parenting they receive, the more affirmed and
confident they will become.
Separated identical twins-Bouchard studied 100
pairs of twins separated at birth and reunited as
adults. He found remarkable similarities in traits,
regardless of environment raised in. Even so they had
differences, somewhat due to the differences in
environment.
“Good Enough” parenting?- Scarr believes people
have such a strong genetic drive to become who we
are supposed to be, that reasonable parenting is
sufficient. Genes will out within a broad range of
environments. Only severe abuse or neglect will
restrict the natural development of a person. This is
seen cross-culturally with a wide variety of parenting
practices still producing functional adults. Good
enough parenting presupposes normal behavioral
practices. Because children also get responses from
many other people beyond the parents, parents can’t
completely mold a child. Baumrind disagreed,
studying parenting styles and finding consistent
differences in how children turn out, depending on
how supportive and guiding the parents are. Parents
need to feel invested in the process to offer children
the best opportunities to fulfill potential. The society
needs to feel invested to continue pouring in
resources into interventions that have positive results,
such as in school success, moderating violence, etc.
Hereditary Influences on Development
Principles of hereditary transmission
Genotype vs. phenotype
Conception
Zygote
Chromosomes
DNA-deoxyribonucleic acid
Mitosis
Meiosis
Multiple births
Monozygotic (identical) twins
Dizygotic (fraternal) twins
Gender determination
Functions of the genes
Dominant-recessive inheritance
Dominant allele
Recessive allele
Carrier
Codominant
Sex-linked characteristic
Genetic imprinting
Polygenic traits
Abnormalities
Congenital defects
Chromosomal Abnormalities
Fragile-X syndrome
Down syndrome
Aging-ova hypothesis
Genetic Abnormalities
Recessive hereditary defects
Mutations
Genetic Counseling
Prenatal Detection of abnormalities
Amniocentesis
Chorionic villus sampling (CVS)
Ultrasound
Treating hereditary disorders
PKU- phenylketonuria
Intrautero fetal surgery
Gene replacement therapy-CF-cystic
fibrosis
Germline gene therapy
Ethical issues
Methods of study of hereditary influences
Behavioral genetics
Heritability studies
Selective breeding studies
Family kinship studies
Twin design
Adoption design
Concordance rates
Heritability coefficient
Nonshared environmental influences
Shared environmental influences
Misconceptions about heritability
Hereditary influences on IQ
Hereditary influences on personality
Introversion/extroversion
Empathy
Hereditary influences on Mental disorders
Schizophrenia
Manic-depression
Neurotic disorders
Canalization principle
Range-of-Reaction Principle
Passive genotype/environment correlations
Evocative genotype/environment correlations
Active genotype/environment correlations
Separated identical twins
“Good Enough” parenting?