Nature Vs. Nurture Flashcards
Nature and Nurture
Today, there is a
consensus that almost all
human characteristics are
influenced by both
genetics (i.e., nature) and
environment (i.e.,
nurture).
- Genes and experience
interact to produce
unique outcomes.
Genes
units of
heredity that maintain
their composition from
one generation to the
next.
Genes come in pairs
because they are aligned
on chromosomes that
also come in pairs.
Chromosomes
are
double-helix strands of
deoxyribonucleic acid
(DNA).
DNA
contains four
nucleotide bases:
adenine, guanine,
cytosine, and thymine.
In a double-helix strand of
a chromosome, adenine
bonds to thymine and
guanine binds to cytosine
the genetic code
The sequence of
nucleotide bases
genotype
The genetic makeup of
an individual
phenotype
An individual’s
observable characteristics
autosomal
chromosomes
22 pairs of the
chromosomes and
contain autosomal
linked genes.
sex
chromosomes
are only a
pair in females.
- Sex chromosomes are
labelled X and Y.
- Females have two X
chromosomes and males
have a X and a Y
chromosome. - The X and Y
chromosome differ in
appearance and carry
different genes. - Genes located on the
sex chromosomes are
called sex-linked genes.
X
chromosome
One example of a sexlinked gene is a gene that
codes for color vision
homozygous
If you have the same
version of a gene on both
chromosomes
heterozygous
If you have different versions of a
gene on both
chromosomes
alleles
Different versions of the
same gene
can be dominant
or recessive (in some
cases they can be
intermediate as well).
- A dominant allele is
expressed in either a
homozygous or
heterozygous condition. - A recessive allele is only
expressed in the
homozygous condition.
messenger
ribonucleic acid
(mRNA).
One of the strands of
DNA then serves as a
template for the
construction of a strand
RNA contains four
nucleotide bases:
adenine, guanine,
cytosine, and uracil.
Genetic Expression
During genetic
expression, the partial
section of the
chromosome that
contains the gene
unravels separating
the bonds between the
nucleotide bases.
transcription
The synthesis of mRNA
from DNA
Translation
The ribosome uses the
strand of mRNA to
construct a protein. The
synthesis of a protein
from mRNA is called
Proteins
chains of
amino acids that form
the structures of the body
and facilitate biological
functions (e.g., enzymes).
codon
Three nucleotide bases
along a strand of mRNA
transfer RNA
(tRNA)
- A ribosome translates
the messenger RNA by
moving along the RNA
bases. At each codon, it
signals to a molecule to deliver the
corresponding amino
acid. The amino acid is then attached to a
growing chain. - This process continues
until the ribosome
reaches a stop codon
which signals that the
protein is complete (see
picture).
Humans have how many genes?
approx.
20000 genes.
- The expression of genes
is controlled by sections
of DNA called
enhancers
or promotor regions
- Enhancers are regulated
by proteins called
transcription factors
that bind to enhancer
regions.
- The interaction between
transcription factors and
enhancers is regulated in
part by environmental
signals
Mutations
Genes can undergo
spontaneous changes
called mutations.
- Genetic mutations can
then be passed to
offspring.
- A genetic mutation
typically does not
increase the fitness of the
individual who inherits it,
however, in some rare
cases it can (e.g.,
FOXP2 gene).
Two other types of
genetic mutations are
duplications and
deletions.
Deletions
occur when
part of a DNA sequence
on a chromosome is
removed.
Duplications
occur when
part of a DNA sequence is repeated.
Most deletions or
duplications are not
beneficial (e.g., Williams
Syndrome).
An example of a disorder
that is caused by a
duplication in the DNA
sequence is Fragile X
syndrome. It affects 1 in
4000 males and 1 in 8000
females.
Fragile X Syndrome
caused by a
duplication in the
enhancer/promoter
region of the FMR1
gene (the Fragile X
Mental Retardation 1
gene) located on the X
chromosome.
- Normally, this region
contains 5 to 54
repeating CGG bases (i.e.,
cytosine, guanine,
guanine). For example,
CGGCGGCGGCGGCGGCG
GCGG.
The full mutation in
the promoter region of
the FMR1 causes the
gene to become
inactivated (i.e., the
gene is not
expressed).
- Therefore, an important
protein called the fragile
X mental retardation
protein (FMRP) is not
synthesized.
- Lack of the FMRP causes
the symptoms associated
with Fragile X syndrome.
a FMR1 gene
premutation.
Some people have a
version of this gene
that contains 55 to 200
repeats of the CGG
segment.
Epigenetics
The relatively new
field of epigenetics
explores changes in
genetic expression as
the result of
environmental
influences.
These changes in
genetic expression occur
without changes to the
underlying DNA base
sequence.
- Epigenetic changes
provide a mechanism
through which genes and
experience interact.
histone
remodeling.
epigenetic
mechanism
DNA wraps around
proteins called histones
(think of string wrapped
around a ball).
- DNA wrapped around
histones is called
chromatin.
- For a gene to be
expressed, DNA must
partially unwrap from the
histones.
- When DNA is wrapped
tightly around the
histones, genes are
unable to be expressed.
- When DNA is unwound
from the histones, genes
can be expressed.
- Experiences (e.g.,
feeling socially isolated)
can alter the chemical
environment in a cell,
which can cause histone
remodeling and changes
in genetic expression.
DNA
methylation
- DNA methylation occurs
when methyl groups
(CH3) bind to the
promotor region of a
gene. - Methylation typically
causes a gene to be
turned off (but not
always). - Methyl groups typically
bind to cytosine bases. - In fact, this is what
occurs in Fragile X
syndrome. The repeated
CGG segment becomes
hypermethylated, turning
off the FMRI gene.
Many types of
environmental factors
that can promote
epigenetic changes.
transgenerational
epigenetics.
epigenetic changes can
be passed from parents
to offspring.
Behavioral Genetics
the study of genetic
influences on individual
differences in
psychological
characteristics and
behavior.
Molecular genetics
focused on identifying the
specific genes associated
with psychological
characteristics and
behaviors (e.g., which
genes are associated with
psychopathy?).
A heritability estimate
provides a percentage of
the amount of trait
variation in a population
that can be accounted for
by differences in
genetics.
- Heritability estimates
range from zero to 100%.
- Heritability estimates
cannot be applied to
specific individuals within
the population that was
used to calculate it.
A heritability estimate
can only be applied to
the population that
was used to calculate
it because it is directly
influenced by the
degree of genetic and
environmental
variability that exists
within a population.
How do behavioral
geneticists calculate
heritability estimates?
- Twin studies compare
the degree of similarity
on a trait between
monozygotic twins and
dizygotic twins. - The higher the degree of
similarity on a trait
between monozygotic
twins compared to
dizygotic twins, the
higher the heritability
estimate will be.
Studies of heritability
estimates using Western
samples have shown that
differences in almost
every trait and behavior
in psychology has a
substantial genetic
influence (i.e., between
40 to 80 percent).
