HUME HOUSE CDC
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• Target Child
• Teacher Meeting
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• Typed doc of observations
HEREDITY AND
ENVIRONMENT:
NOT WHICH ONE IS IT,
NOW HOW MUCH OF
EACH, BUT HOW?
Sharon Carnahan, Ph.D.
OVERVIEW
• Our genetic substrate interacts with environmental influences in
complex ways
• Genes provide the raw materials to shape and be shaped by the
environment
• Developmental psychologists are interested in specific applications of
genetic information
• Practical applications and ethical quandaries surround genetics
FROM ONE CELL TO TRILLIONS
• Gamete = reproductive cell
• Male gamete = sperm
• Female gamete = ovum (egg cell)
• Growth begins
• Male and female gametes fuse and become a zygote
• Zygote begins process of duplication and division
• At the eight-cell stage differentiation begins
THE GENETIC CODE
• Gene = basic unit for transmission of
heredity instructions
• Genes are discreet segments of a chromosome
• Chromosome = genetic material child
inherits from parents.
• Each parent contributes 23 chromosomes.
• The 23 pairs of chromosomes carry between 30,000 and 40,000 distinct
genes
KARYOTYPE
IS A PICTURE OF ALL 23 PAIRS IN
ORDER
• What can you tell about the fetus from looking at a
karyotype?
• Sex
• Major chromosomal anomalies like trisomy 21, Penta X,
Klinefelter’s XXY, Turner XO
SPECTRAL KARYOTYPE (SKY) =
VISUALIZATION OF ALL OF AN ORGANISM’S
CHROMOSOMES TOGETHER, VIEWED WITH
FLUORESCENT DYE
CHECK POINT
PUT IN ORDER OF SIZE
Gene
Chromosome
Nucleus
Cell
A-T Base Pair
CHECK POINT
IN ORDER OF SIZE
BIGGEST
CELL
TO
NUCLEUS
CHROMOSOME
SMALLEST
GENE
A-T BASE PAIR
THE HUMAN GENOME PROJECT
• The Human Genome Project was the international research effort to determine
the DNA sequence of the entire human genome.
• Human Genome Project Results. In 2003, an accurate and complete human genome
sequence was finished two years ahead of schedule and at a cost less than the original
estimated budget.
________________________________
99% of all human genes are basically the same
worldwide and are shared with many other species of
animals
• Regulator genes guide growth & development and make
up the 1% differentiation between species
CHROMOSOMES
Genetic code = sequence in which pairs of chemical bases appear
along each segment of DNA molecule
• Each person has 46 chromosomes or 23 pairs of chromosomes
• One set is inherited from the mother and one from the father
• This pairing encoded for life in every cell except in gametes
• sperm and ova, each of which have only 23 chromosomes
SEX DETERMINATION
• Sex determination
• Twenty-third chromosome pair =
determines the zygote's sex
• XX = twenty-third pair in the
female, one X from the father and
one from the mother
• XY
= twenty-third pair in the
male, the X from the mother and
the Y from the father
How does this ratio change with age? Why?
Is this a pos or neg correlation?
THE MECHANISMS OF DIVERSITY
• Vast number of chromosome combinations possible.
• 8 million chromosomally different ova or sperm
produced by an individual
• = 64 trillion possibilities between one mother and
father
STUDYING HEREDITY &
ENVIRONMENT: TWINS
• MONOZYGOTIC
TWINS
• Formed from a
single zygote which
splits after
fertilization
• Identical genetic
info
• DIZYGOTIC TWINS
• Formed from 2 different
zygotes which then implant
• As alike as any two siblings
• Occurs once in 60 births
• Women in late 30s are
three times as likely as
younger women to have
dizygotic twins
DZ TWINS
• Dizygotic (DZ) twins, also called fraternal twins, occur
when two egg cells are each fertilized by a different sperm
cell in the same menstrual cycle.
• DZ twins are about twice as common as MZ twins, and
they are much more likely to run in families.
• Compared with the general population, women with a
mother or sister who have had DZ twins are about twice
as likely to have DZ twins themselves.
• DZ twinning is thought to be a result of hyperovulation,
which is the release of more than one egg in a single
menstrual cycle.
ARTIFICIAL INCREASES
IN THE TWIN POPULATION: TROUBLE
• Number of multiple
births has doubled
in last decade due
to methods of
helping infertile
couples such as
fertility drugs
• Ethical concerns?
DISCORDANT TWINS
HEREDITY, ENVIRONMENT, AND
THE QUESTION HOW?
• Concordance rate = rate at which a disorder
develops in both twins
• Bipolar disorder
• 65% concordance in identical twins
• 21% concordance for fraternal twins
• 40% for schizophrenia in identical twins
THE BUSINESS OF CONCEPTION
• Sex weekly for a year =
• Infertile couples are defined as couples who
cannot produce a baby after one year of
trying
• Many are helped by assisted reproductive
technology (ART)
• Example: in vitro fertilization
• (IVF)
FROM GENOTYPE TO PHENOTYPE
• Genotype =
• person’s genetic inheritance
• Phenotype =
• genetic inheritance that can be observed or is expressed
• Polygenetic traits =
• characteristics produced by gene interaction
• Multifactorial traits =
• characteristics produced by gene and environment interaction
CHECK POINT
DEFINE THESE TERMS
Genotype
Phenotype
Polygenetic traits
Multifactorial traits
The Human Rainbow
Multifactorial inheritance:
•The type of hereditary
pattern seen when there is
more than
factor involved and when
there are also
environmental factors
participating in the
causation of a condition or
trait.
•SIMPLE: height
•COMPLEX: Autism
An important idea which helps us to
understand why one person is affected,
while a close relative or sib is not.
The liability-threshold model is a threshold model of categorical (usually
binary) outcomes in which a large number of variables are summed to yield an overall
'liability' score; the observed outcome is determined by whether the latent score is
smaller or larger than the threshold.
AKA RISK INDEX
The liability-threshold model is frequently employed in medicine and genetics to model
risk factors contributing to disease.
In a genetic context, the variables are all the genes and different environmental
conditions, which protect against or increase the risk of a disease,
and the threshold is the biological limit past which disease develops.
The threshold can be estimated from population prevalence of the disease (which is
usually low).
The model explains more common diseases which have many genes and also an
environmental component.
CHECK POINT:
SKETCH A PICTURE & GIVE EXAMPLE:
THRESHOLD THEORY
DOMINANT & RECESSIVE GENES
• Dominant gene =
stronger of an
interacting pair of genes
• Recessive gene = weaker
of an interacting pair of
genes
• Example:
• Cystic fibrosis is an autosomal recessive
disorder
• If normal allele dominates, child with a
heterozygous genotype will not show the
disease
• If the 2 codominate, then see both
• (AB type blood)
• (Five Feet Apart)
X-LINKED TRAITS ARE LINKED TO THE X
CHROMOSOME & ARE USUALLY RECESSIVE.
GENES LINKED TO X
CHROMOSOME
If X-linked genes are recessive and harmful,
it is critical to know if a parent is a carrier.
• Male has one X and one Y chromosome and female has two X chromosomes
• Female’s recessive gene can be counterbalanced by the other X, but male’s
cannot because there is only one X
• Color blindness and some allergies, diseases, and learning disabilities are
caused by recessive X-linked genes
CHECK POINT: X LINKED TRAITS
• X linked traits are seen
far more often in males
than in females (XY).
• WHY?
• Red green color blindness
• Haemophilia A
HEREDITY AND ENVIRONMENT:
TYPES OF GENETIC DISORDERS
(KNOW ONE EXAMPLE OF EACH)
• A single, dominant, defective gene
• Huntington’s Disease
• Pairs of recessive genes
• TAY SACHS DISEASE
• Inborn errors of metabolism
• PKU
• X linked recessive = seen more often in males
• Color blindness, some learning disabilities, haemophelia
• Sex linked = of the gametes
• Turner’s XO, Kliinefelter’s, Penta X
• Extra or missing autosomal genetic material
• Down syndrome & trisomy 13, 18
• Most cases of “wrong number of chromosomes” are miscarried
WHY NOT 100%, IF
INHERITED?
epigenetics
WEEK 2
EPIGENETICS
Read, What is Epigenetic Theory? 1 & 2