Genetics Flashcards
models of nature vs. nurture relationship
- all nature/all nurture
- additive model
- interactive model
- transactional model
all nature/all nurture model
can’t use these models -> every physical psychological and physical trait have some influence from both nature or nurture
additive model
- each trait is sum of nature vs. Nurture
- this lacks complexity -> it looks at nature vs. Nurture one time and assumes they’re binary (either low or high)
- simple and linear
interactive model
- nature and nurture exist on a spectrum and interact together to create outcomes
- however, this focuses on one time only
- non-linear (like plants growing at different heights)
transactional model
- recognizes that nature and nurture interact constantly throughout the lifespan
- nature and nurture influence each other
- spectral
genotype
- genetic material an individual inherits; constant across the lifespan
- Genetics can change, but the code/genotype itself cannot
phenotype
- observable characteristics of the genotype, including physical and behavioural characteristics
- Ex. Eye colour, outgoing behaviour
environment
every aspect of the individual and her experiences other than the genes themselves
epigenome
- heritable chemical changes to gene expression
- Epigenome tells genome when/how to work -> tells our cells which cells they should be (hair, heart, etc.) by turning them on/off
chromosomes
- 46 chromosomes -> 23 pairs
- One chromosome from each pair comes from each parent
DNA
- Genetic info made of long strings of DNA -> building blocks of genetic material
- DNA made of base pairs
- Every cell in your body has the same DNA
if every cell in your body has the same DNA, why aren’t all your cells the same?
- Some genes are turned on/off at different points in development or at different locations to create different cell types, etc.
- Ex. Genes that are responsible for secondary sex characteristics are present throughout the life time, but aren’t turned on until puberty
- Ex. Genes that are responsible for red blood cells are never turned on in hair cells
5 types of nature/nurture interactions
- Parent’s genotype -> child’s genotype
- Child’s genotype -> child’s phenotype
- Child’s environment -> child’s phenotype
- Child’s phenotype -> child’s environment
- Child’s environment -> child’s genotype
Parent’s genotype -> child’s genotype
- Variations in genetics amongst children from the same parents
- due to random assortment, crossing over, and/or mutations
random assortment
- You only get 1 chromosome for each pair from each parent, and whichever one you get is random
- Chromosomes are shuffled in the process of gamete (egg and sperm) formation
- Unlike all our other cells, gametes only have 23 chromosomes
- Results in 2^23 possible combinations -> chances are genetically 0 that two sperms/eggs will be the exact same
crossing over
Division of germ cells in embryonic development results in shuffling of DNA sections
mutations
- Errors in DNA transcription
- Some mutations are invisible, but some create inviable gametes/fetuses (resulting in fetal death), or maladaptive characteristics
- A minority of mutations are adaptive rather than maladaptive -> result in gradual evolution of the species
Child’s genotype -> child’s phenotype
- Although every cell in the body contains all of an individual’s genetic material, only some of those genes are expressed at a given time
- Some are switched on during cell differentiation (eg. To form limbs, brain cells, blood cells)
- Activated/deactivated by regulator genes
- Some recessive genes are never expressed at all
- Most of the differences between humans are due to gene expression, not genetic differences (1-1.5% variation in the population)
Child’s environment -> child’s phenotype
- Norm of reaction: the range of all phenotypes that could theoretically result from one given genome
- Growing up in a rich vs. Impoverished environment can influence the expression of genes
- Ex. Genetic predisposition to be taller than average, but undernourished as an infant -> end up at average height
- Ex. Genetic predisposition to be extroverted, but experience trauma as an infant -> introverted
Genetic experiences put you in a certain range, but your experiences move you up or down in the range
Child’s phenotype -> child’s environment
- Reflects the active child theme
- Children change their own environments based on their phenotypes
- Ex. A child with a predisposition for low sustained attention may choose activities that require less attention
- Ex. Choosing to be active and play outside rather than sitting in once place and reading a book
Child’s environment -> child’s genotype
- Environment can cause changes in gene expression
- Epigenetics
- Gene silencing: methylation (addition of methyl group to DNA) prevents transcription
- While one’s genome is constant throughout lifespan, the epigenome changes
shared genome in humans
- Humans share 99% of the human genome
- Gene expression is what changes in order to make us different from each other
- Allows us to have genetic similarities but phenotypic differences
epigenetics
- The fifth type of nature-nurture interaction (child’s environment – child’s genotype)
- Experience mother has affects genetic expression in offspring, and that epigenetic change is inheritable by the next generation
- Genetic expression = turning on/off
- Can change during critical periods (ie. Pregnancy, puberty)
Human and non-human epigenetics examples
- Rats: changing pregnant rat diet to create obese or thin offspring (and offspring of that offspring)
- People: famine post-WWII affected babies of mothers who had gone through the famine (even though the famine happened before they got pregnant) -> ex. Offspring had difficulty regulating body weight. This was also shown in the grandchildren of people who experienced famine
forebrain vs. midbrain vs. hindbrain
- Forebrain: structures responsible for cognition, perception, etc.
- Midbrain: responsible for basic functions (ex. Transmitting info from spinal cord to brain)
- Hindbrain: primitive, responsible for basic functions (ex. Respiration)
infant brain development - brain structures and timing
- 3 main brain structures differentiated at 26 days -> midbrain and hindbrain are quite large at this stage
- Once born, baby’s brain structures and sizes are quite similar to our own adult brains
neurons
- Cells in nervous system that communicate with one another to perform information-processing tasks
- 100 billion of them; make up grey matter
- Pass information to each other so we can do things
- 3 main types of neurons: Sensory neurons, Motor neurons, Interneurons
- billions of neurons throughout the body
sensory neurons
- Communicate information from outside world to brain
- ex. Sound, touch, taste, odor, vision
motor neurons
- Communicate information from spinal cord to muscles
- Allows us to move
interneurons
- Connect sensory neurons, motor neurons, or other interneurons
- Most common
cell body
cell’s life support centre
nucleus
contains chromosomes with DNA
dendrites
receive messages from other cells
axon
passes messages away from cell body to other nuerons, muscles, or glands
neural impulse/action potential
electrical signal traveling down the axon
terminal branches of axon
form junctions with other cells
myelin sheaths
- Covers the axon of some neurons to help speed up neural impulse
- Breaks in between myelin = nodes of Ranvier -> speed process up -> signal can jump from sheath to sheath
- Formed by glial cells (support cells)
neural tube formation
1-2 day old embryo has formed into ectoderm (outer layer), mesoderm (middle layer), and endoderm (inner layer)
ectoderm
- skin cells, neuron on brain, pigment cells
- As new cells are added to the ectoderm, the neural groove begins to form
- As the groove closes, the neural tube is formed
This neural tube will eventually form the brain and spinal cord
mesoderm
- cardiac and skeletal muscle cells, kidney tubules, red blood cells, smooth muscle cells in gut
endoderm
- lung, thyroid, and digestive cells
neurogenesis
- Cell division in the new neural tube occurs rapidly starting in the 3rd/4th week of gestation
- Neural stem cells divide -> some become neural support cells or glial cells, small amount become neurons, about half die off
- Complete by 18 weeks
- New neurons then migrate to their permanent location and form axons and dendrites to communicate with other neurons
myelination (when it happens, what it does)
- Myelin sheaths necessary for information transmission are mostly formed in the third trimester of gestation
- Much myelin production occurs after birth in the infancy, childhood, and adolescent years
- Speeds up information processing
synaptogenesis (when does it happen)
- A lot of synaptogenesis occurs before birth
- However, visual cortex synaptogenesis peaks right after birth since we can finally see
- Prefrontal cortex continues to increase through toddler-hood and into the early elementary school years
synaptic pruning
- There is an overaboundance of synapses at birth, resulting in exhuberant connectivity (may result in infant synesthesia, since it’s much more common for infants than adults)
- These synapses are slowly pruned away after birth throughout infancy, childhood, and adolescence
- Synaptic pruning occurs by: Axon degeneration and shedding, and Axon retraction
- Sensitive periods and plasticity in development -> infant brain much more plastic and malleable than adult brain is -> exuberant connectivity allows for easier learning -> this gets pruned throughout the development
genes
- segments of DNA
- anology: If DNA is a building, genes are rooms in that building
- humans have 21,000 genes and share most of them with all living things
alleles
- 2 or more different forms of a gene
- can be dominant (gets expressed) ex. brown hair, or recessive (not expressed if dominant allele is present) ex. blonde hair
homozygous vs. heterozygous
- homozygous: having two of the same alleles for a trait
- heterozygous: having two different alleles for a trait -> only dominant one is expressed
norm of reaction
all the phenotypes that can theoretically result from a given genotype in relation to all the environments in which it can survive and develop (ex. plants growing at different altitudes)
behaviour genetics
- science concerned with how variation in behaviour and development results from combo of genetic and environmental factors
- why are we different?
- traits that are polygenetic (affected by many genes) and multifactorial (affected by many environmental factors) can account for diversity
cerebral cortex
grey matter of brain that plays a primary role in “human-like functioning” - seeing, hearing, writing, feeling emotion, etc.
spines
- formations on the dendrites of neurons that increase the dendrites’ capacity to form connections with other neurons
- part of neurogenesis
experience-expectant plasticity
- the role of general human experience in shaping brain development - ex. patterned visual stimulation, voices and sounds
- the brain can rely on and expect input from these sources to help shape it and fine-tune it
experience-dependent plasticity
the process through which neural connections are created and reorganized throughout life as a function of an individual’s experiences
sensitive period for brain damage
- has worst effects during prenatal development and in the first year after birth, when neurogenesis is occurring
- if damage occurs in early childhood, there’s a good chance the brain can rewire itself and recover
body development
- humans spend 20% of life growing
- growth of body parts is uneven -ex. head measures 50% of body at 2 months, but 10% at adulthood
- proportion of body fat is greatest in infancy and decreases into early childhood
failure to thrive
a condition in which infants become malnourished and fail to grow or gain weight for no obvious medical reason
breastfeeding and cognitive development
has positive effect on cognitive development and may increase IQ scores
what can infants taste?
sweet, sour, bitter
