Genetics and Epigenetics Flashcards
Nature and Nurture
Both heredity and
environment influence individuals’ characteristics
– Use to emphasize one factor or the
other as the prime influence.
– only about 19,000 genes in human
genome
– we differ from one another by only
about 1 to1.5% of our genes
– Indeed, many genes conserved
across species
– which genes are turned on, when, &
for how long – and the background
context in the organism -determines
who we are as a species, &
accounts for most individual
differences
genotypes and phenotypes
genotypes: unique genetic makeup of an individual - what could be
-comes from parents
phenotype: refers to the obervable characteristics of an individual (phychological and physical) - what it is
-comes from parents and enviroment
genotypes > phenotypes (when the enviroment allows so)
Parents’ and Child’s Genotypes
- Genetic material is
passed on as chromosomes-long,
threadlike molecules made up of DNA
– Carry instructions involved in
the formation and functioning
of an organism
cell>chromsomos>DNA>genes
– Genes, sections of
chromosomes: basic units of
heredity for all living things
– Most of the DNA is non-
coding
Karyotype
What does this mean?
Yes, there are profound genetic influences on our bodies
and our behavior
- Work investigating genetic differences in abilities,
personality, disabilities, etc. - But each genetic trait has a norm of reaction
- The extent and timing of expression changed by environment
- Indeed, whether or not it is expressed at all can be
determined by the environment - Remember both evocative and active gene-environment
interactions - But even when passive gene-environment interactions,
the outcome is not deterministic
Norm of Reaction
Refers to all the phenotypes that
could theoretically result from a given
genotype, in relation to all the
environments in which it could
survive and develop
Human Examples
PKU
– enzyme deficiency that
➔ progressive cognitive
deficits & seizures
- mitigated by phenylanine
free diet: dose & timing
effects
MAOA
- severe maltreatment
increases likelihood of
antisocial behavior in males
- effect much stronger if a
relatively inactive MAOA
gene.
How does this happen
- Genes code for proteins
- Proteins → structures
- And, indirectly, for traits
- But many also regulate other genes
- The environment effects all of these
DNA
- 46 chromosomes, 23 pairs
- Each made up of long strands of DNA
- Organized in base pairs
- Genes are segments of DNA
- Genes code for proteins
- Also, many genes are regulator genes: turn other genes on and off
- non-coding DNA may play regulatory roles
- Most traits are polygenic – influenced by multiple genes
– Every cell in your body has the same DNA
– But different genes are turned on or off at different points in development or at different locations, to create different cell types, transporter molecules, etc
- Most traits are polygenic – influenced by multiple genes
Chromatin
is the combination of DNA and other proteins that make up the contents of the nucleus
Histones
are the chief proteins in the chromatin acting as spools
around which DNA winds
When does DNA get expressed?
- To be expressed, DNA needs to be loosened from histones
- And methyl group needs to be removed:
– So typically, demythlated genes are expressed
– And methylated genes are silenced - The environment influences methylation, and other epigenetic
processes
Epigenetics
- Epigenome – “above the genome”.(it added)
- Epigenetics: Genes stay the same – but their activation profiles change due to experiences and lifestyle
- So – across the lifespan your “genome” is constant, but your “epigenome” changes
-
The science of epigenetics
– Changes in the genome that are brought about through experience and can be passed on to the next
generation – likely through extracellular matrix
– sequence of amino acids is the same, but whether the
genes are turned on or not changes
methylation
Human Studies: Krol et al (rec) reading:
Epigenetic dynamics in infancy and the impact of maternal engagement
- Effect of maternal care on expression of “conserved regulatory sites” in the oxytocin receptor gene OXTR
- Tested methylation (OXTRm) in mother and infants, with
infants at 5- and 18 months of age - Measured maternal behavior in free play task at 5 mos
- Results: high correlation between maternal and infant methylation, but only infant methylation patterns dynamic
- Infant methylation changes bet 5 & 18 mos correlated with maternal behavior: engaged → more demethylation
- Infant temperament at 18 mos correlated w/methylation
– Assessed temperament: Early Child Behavior Questionnaire
Human Studies: Early Adversity
Dutch Hunger Winter, 1944
– Nazis cut-off trains ➔ famine
– If famine in1st trimester, normal birth weight, but later obesity
– If in 2nd & 3rd trimesters, SGA, and later obesity
– In both, also adult diabetes
– & earlier cog decline in aging
- Transgenerational effect:
– Their children also at greater risk for adult diabetes
– Could feeding the mothers a dietary supplement break the
cycle? Looking for such
Developmental Implications: Early
Adversity
- Epigenetics
– How early negative experience can have lasting effects
– And even inter-generational transmission - Has implications for health
- Has implications for well being
