Lecture 2: Heredity, Brain, Prenatal Flashcards
What is a Genotype?
the genetic material an individual inherits
What is a Phenotype?
the observable expression of the genotype, including body characteristics and
behavior
What is Environment?
includes every aspect of the
individual, and his or her surroundings, other
than genes
What are Chromosomes?
structures found in the nucleus of living cells— carry genetic information
What is DNA?
Each chromosome is a single molecule of DNA (deoxyribonucleic acid),
What are genes?
– The basic units of heredity
– Each chromosome consists of thousands of genes, small segments of DNA
– Genes contain “instructions” for building specific proteins
– A gene is “expressed” if it has been turned on to make its specific protein
What cell did each complex human start with?
The ZYGOTE
– ZYGOTE = sperm (23 chromosomes) + ova (23
chromosomes)
– So each parent contributed half of your genetic
makeup
What are ALLELES?
The same gene has multiple different forms; these are called ALLELES
- You have 2 alleles for every gene – 1 from each parent
– HOMOZYGOUS
– HETEROZYGOUS
Phenotypic plasticity?
The degree to which
environmental factors affect a given trait
Canalization?
Certain characteristics are restricted in their outcome, even if the environment varies widely
- i.e., they are less susceptible to variations in the
environment
– Example: language
What is Norm of Reaction?
The range of possible phenotypes for a given
genotype
Epigenetics?
The complex, dynamic process
through which environments shape the expression of genes
Four different ways of gene-environment interacting?
- Environmental factors turn genes on/off
- Environmental factors alter magnitude of genetic effects on development
- Gene expression can affect how people respond to children – “evocative”
- Genotype affects the types of environments the person seeks out – “active”
What are neurons?
Neurons are communication
cells, there are approx 100 million
What are Synapses?
connective spaces
between neurons
What are Glia?
supporting cells that
produce myelin
What are the Stages of Brain Development?
- Neurulation
– Formation of neural tube - Neurogenesis
– Birth and migration of neurons - Circuit formation
– Synaptogenesis and synaptic pruning - Myelination
– Formation of fatty covering on axons
What is Neurulation?
Neurulation happens 3 weeks after conception. Neural tube forms from the ectoderm, and cells inside the tube form the CNS; cells outside the tube form the PNS
What are the four lobes of the cerebral cortex ?
Frontal Lobe: Movement, attention, impulses
Partial Lobe: Touch, pain, body position
Occipital Lobe: Visual Lobe
Temporal Lobe: Smell, taste, hearing, language
What is Neurogenesis?
Proliferation of neurons through cell division and Neuron migration where they move to appropriate place in the brain
What is Circuit formation?
Most rapid during pre and postnatal periods, Overproduction: many more synapses are produced than will actually be used
What is Synapse pruning?
Experience determines which synapses will live or
die – the “USE IT or LOSE IT” phenomenon. Timing of pruning also varies across brain regions
What is Myelination?
Glia produce myelin: a lipid/protein substance and then Myelin insulates axons so that signals can travel
faster
Developmental Plasticity
The degree to which, and the conditions under which, brain development is open to
modification by the environment
- The effect of an experience on the brain
depends on:
– TIMING
– DOSE
– DURATION
HOW does experience influence the developing brain?
There’s two different experiences
1. Experience-expectant plasticity
2. Experience-dependent plasticity
What is experience-expectant plasticity?
The ability of the brain to adapt in response to sensory information is referred to as experience-expectant plasticity
– Due to pruning of synapses that were overproduced
– Sensitive periods
Examples of experience-expectant plasticity?
– Vision
– babies born with cataracts
– Language
– Genie
Critical period?
A very narrow period during which a particular experience must occur for development to proceed normally
- Example: Imprinting in chicks
Sensitive period?
A developmental stage during which the brain is most
susceptible to experiences, but changes are still possible
outside of this window
Experience-dependent plasticity?
Changes in the brain due to an individual’s unique
personal experiences
– Due to formation of new synapses throughout the
lifespan
Experience-dependent plasticity examples
– Adult violin players
– London cab drivers
Germinal period
days 0-14
From conception to implantation in uterine wall (zygote)
Embryonic period
weeks 3 – 8
Formation of major organs
Fetal period
week 9 – birth
– Organ systems begin to function
– Significant growth
How long does it take the zygote to become a fetus ?
Zygote has full complement of genetic material, half from each parent Takes about 266 days for the one-celled zygote to become a fetus of 200 billion cells
Discuss The Germinal Period: (2 weeks)
Zygote travels towards
uterus
**By the 4th day after conception, the
zygote arranges itself into a hollow sphere of cells (the blastocyst) with a bulge of cells, the inner cell mass, on
one side.
**Blastocyst implants in uterine wall:
–Inner layer (embryonic disc) becomes embryo
–Outer layer (trophoblast) becomes:
*Amniotic sac
*Placenta
*Umbilical cord
What is Cleavage?
The division of the zygote
into many cells. It Occurs while the zygote travels down the fallopian tube towards uterus
Discuss The Embryonic Period (3-8 weeks)
The embryonic period spans the time of implantation to about the eighth week of pregnancy. During the embryonic period, cells of the embryo (the inner cell mass called the embryonic disk) begin to differentiate into specialized cells and brain regions that take on different forms and serve unique functions.
During the embryonic period, what three layers do the cells fold to?
- Ectoderm
- Mesoderm
3.Endoderm
What is Ectoderm?
The outer layer or ectoderm develops into the nervous system, sensory organs, the nails, teeth, and the outer surface of the skin.
What is Mesoderm?
The middle layer or mesoderm develops into muscles, bones, the circulatory system, inner layers of the skin, and other internal organs.
What is Endoderm?
The inner layer or endoderm develops into the digestive and respiratory systems.
What is cephalocaudal development?
Areas near the head develop earlier than those farther down, in a pattern referred to as cephalocaudal development—head before body; arms before legs.
What is proximodistal development?
Embryonic growth also is characterized by proximodistal development, with areas near the center of the body developing before areas toward the periphery
What is the important milestone during week 3 of embryonic period?
– 3rd week
* Neural tube (from ectoderm) becomes the brain and
spinal cord; major areas of the brain begin to divide
What is the important milestone during week 4 of embryonic period?
– 4th week
* Heart begins beating; limbs, eyes, ears, and digestive
system begin to form
What is the important milestone during week 5 of embryonic period?
– 5th week
* Lungs begin to form
What is the important milestone during week 6 of embryonic period?
– 6th week
* Head becomes dominant; brain is differentiated
What is the important milestone during week 7 of embryonic period?
– 7th week
* Nerve cells form in the brain; muscles differentiate;
sexual differentiation
What is the important milestone during week 8 of embryonic period?
– 8th week
* Ears are fully formed; fetus is capable of moving
What is the fetal period?
The fetal period lasts from about the ninth week of pregnancy to birth, and involves impressive changes in fetus size, brain development, sensory capacities, and learning
How does fetal period affect growth and organ systems?
A period of rapid growth and refinement of organ systems
– From 1½ to 20 inches
– From 0.02 to 7.1 pounds
- Fetus becomes more responsive
What is Habituation?
the fetus decreases responses to repeated or continued
stimulation, then increases
response to new sound
Do newborn infants recognize
rhymes and stories presented before birth?
YES. example - cat in the hat, or native language
Do newborn infants recognize smell and taste?
YES newborns also prefer
smells and tastes that are
familiar because of
prenatal exposure
What are Teratogens?
Any disease, drug, or other environmental agent that can harm a developing embryo or fetus
What are some possible teratogens?
– Maternal diseases
– Drugs
– Environmental hazards
What are the three key factors determine the magnitude of a teratogen’s effects?
- Timing of exposure
- Amount and length of exposure (dose-response
relation) - Genetic susceptibility of the fetus
What Is timing of exposure?
Teratogens affect the organs that are developing at the time of exposure, and may have no effects at all during certain prenatal periods.
What is Amount and length of exposure (dose-response
relation)?
The amount of the harmful substance that reaches the fetus will determine the extent of abnormal development, which can range from no effect at all to fetal death.
What is the Genetic susceptibility of the fetus?
For example, although thalidomide was tested on animals and found to be safe, the unique genetics of humans made fetuses susceptible to its negative effects.
What other hazards are there for the fetus?
- Nutrition
– Severe malnutrition in the mother - babies born low
birthweight, later cognitive deficits - Stress
– Prolonged and severe emotional stress is associated with stunted growth, prematurity, low birthweight, and irritable infants - Age
– Prime time for childbearing: 16-35 years
