Transcript Class 2 - Biological Beginnings

Psych 125
Human Development
Christopher Gade
Office: 1031-G
Office hours: Tu 12-1:30 and by apt.
Email: [email protected]
Class: T 1:30-4:20 Room 2210
Biological Beginnings
• At one point in time in each of our pasts, we
were one cell
• These cells contained a very
special code that was transferred
to every cell replicated from this
first cell
• These codes determined a very, very large
portion about who we are today, who we
were in the past, and who we will be in the
future.
More on the “Code”
• Your “code” was contained within
the nucleus of these cells on
threadlike structures called
chromosomes
– Deoxyribonucleic acid (DNA) – a
complex molecule that contains
genetic information and has a
double helix shape
– Genes – units of heredity
information composed of DNA;
Genes direct cells to:
• A) reproduce themselves
• B) assemble proteins that direct cell
growth and body processes
More on Genes
• Genes not only determine how your cells are
going to multiply and grow, they determine a lot
about who you are and how you’re going to
develop
• We now believe that the average human cell
contains approximately 20,500 genes
– Human genome – the complete set of genes
contained within a human being
– Note: genes are outnumbered by proteins, this
indicates that the genetic code in these genes
collaborate with each other, and can be turned on
and off due to these collaborations
– Computer programming analogy
Looking Closer at the Code
• Each of our genetic
combinations are located on
strands called chromosomes.
Each person has 23 pairs of
chromosomes (e.g. 4
chromosomes total).
• Most chromosomes in
humans look very similar
under the microscope,
except for one.
How do cells
multiply?
• Mitosis – the cell’s nucleus,
including chromosomes
multiply
• Meiosis – the cell’s nucleus
multiplies, but instead of
splitting into two different
cells, it splits into four cells
(gametes)
– Cool fact #1: this type of
replication occurs only in the
testes in males (sperm) and the
ovaries in females (eggs)
– Cool fact #2: that means in every
cell produced by meiosis can
have a very different
combination of genes
So where does the first cell come from?
• Fertilization – the fusing of a sperm cell with an
egg cell that creates one cell (zygote) with a full
set of 23 paired chromosomes
– Note: this fusion causes us to share
approximately half of our genes with
each of our parents, but makes it so
we’re never exact replicas of our
parents
– Identical twins – siblings that came from the same
zygote that split into two identical persons
– Fraternal twins – siblings that came from two
separate fuses that occurred during fertilization
Let’s do a little math…
• In groups of 3-4, come up with a list of six
observable characteristics (e.g. eye color). Then
determine for yourselves how many of these
characteristics came from a) your mother, b) your
father, or c) neither
What’s with all the imbalance?
• Genotype – the sum total of all genetic material
• Phenotype – the sum total of all the observable
characteristics of a person
• Phenotypes aren’t usually easy to predict within
individuals because of:
– Dominant and recessive genes
– Polygenetic inheritance – phenotypes that result from
the interaction of multiple genes
– Heredity-environment interactions
• Epigenetic view – development is the result of ongoing
biological interaction between heredity and the
environment
– Mutations
How brownhaired parents
can have a
blond-haired
child: the gene
for blond hair is
recessive
B Brown
hair
Blond
b hair
Father
Bb
B B
B b
Mother
Bb
B b
b b
Now Onto The Cell Multiplying…
• We know how cells split, but we’re more than
a mere blob of cells, we’ll discuss why that is
after the break.
From a Single Fused Cell to Birth
• Developmental scientists believe that our
development from fertilization to birth can be
split up into three different periods:
– Germinal period (0-14 days after conception)
– The embryonic period (2-8 weeks after conception)
– The fetal period (8 weeks to birth)
The Germinal Period (0-2 weeks)
• The fertilized egg is called a zygote in this period
• The original cell multiplies rapidly (mitosis) in this
stage (over 100 cells by 1 week)
• Two masses of cells already begin to form in this
stage
– Blastocysts – inner mass of cells
that will eventually develop into
the embryo
– Trophoblasts – outer layer of cells
that later provide nutrients and
support for the cell
• Implantation – the attachment of
the zygote to the uterine wall of a
female – marks the end of this stage of development
The Embryonic Period (2-8 weeks)
• After the blastocysts attach to the uterine wall
• Cells multiply faster in this period
• The cells diversify even further
(organagenesis - organ formation)
– Endoderm – digestive/respiratory systems
– Ectoderm – nervous system, sensory receptors
– Mesoderm – circulatory, bones, muscles, excretory and
reproductive systems
– Life support system
• Amnion - protective envelope that eventually contains amniotic
fluid
• Umbilical cord – arteries and vein that connect the baby to the
placenta
• Placenta – a group of tissues that intertwine with the mother and
is used for for sharing of small molecules between the mother
and child
• Neural tube, a collection of cells
Brain
that will form the brain and
Development nervous system develop during
at this Stage this period
– Located on the embryo’s back
– Forms between 2 to 3 weeks after
conception
– Must close or severe birth defects
occur
• Ancephaly – highest regions of the
brain fail to develop
• Spina bifida – lower regions of the
neural tube fail to close, resulting in
varying levels of paralysis
After the Neural Tube Closes
• Neurogenesis – massive reproduction of the cells in this
tube (become the nervous system)
and
• Neuronal migration – the moving
and formation of nervous system
structures
• Synapses – connection between
neural cells called neurons
– video
occur after the neural tube has closed
The Fetal Period – (8 Weeks to Birth)
• Human growth is often split into three trimesters,
the fetal period begins in the last 1/3 of the first
trimester
The Second Trimester
Point of Possible Survival Outside the Womb
The Third Trimester
At Birth
•
•
•
•
Little to no control over most muscles
Horrible visual abilities
23 million neurons in the brain/nervous system
Apgar scale – identifies ability to handle stress and highrisk infants
• A few reflexes (Rooting, Sucking, Grasping, Babinski, Stepping)
Abnormalities
• Though most births follow a very set pattern,
there are a lot of things that can go wrong
during the time from conception to birth.
• In this last section, we’ll discuss both the
nature, and the proposed causes of these
problems that can arise.
Chromosomal Linked Abnormalities
• Meiosis usually occurs without problem, but when it does,
a number of problems can occur when these problematic
gametes successfully fuse with other gametes.
– Down syndrome - physical indications and retardation of motor
and mental abilities
• an extra copy of chromosome 21 is found
• 1/700 births, related to mother’s age at birth (16-34 OK)
– Klinefelter syndrome – underdeveloped testes, enlarged
breasts, and very tall (male)
• an extra X chromosome (23)
• Recently linked to other mental and physical impairments
• 1/800 births
– Fragile X syndrome – shortened attention span and hindered
learning abilities (autism-like behaviors)
• X chromosome structural problems (23)
• Impacts males (1 X) more than females (2 X’s) (1/3600, 1/4000-6000)
Other Chromosomal Abnormalities
• Turner syndrome – Short in stature, webbed neck.
Usually infertile.
– Only one X chromosome (female)
– 1/2,500 births
• XYY syndrome – Linked to height,
aggression, and cognitive skills, but
minimal effects if any.
– extra Y chromosome in the male (23)
– 1/1,000 births
• Note: there are many more chromosome and
mutation linked disorders that are out there,
these are merely a small list.
Environment Linked Abnormalities
• Teratogen – any agent that can potentially cause a
birth defect or negatively alter cognitive and
behavioral outcomes.
– Teratogens impact babies based on when they are
introduced and how much is introduced
– Teratogens come in a number of forms (drugs – both
prescription and recreational , diets, maternal
diseases, maternal stress) and impact newborns in a
number of different ways
Developmental Periods and Teratogens
Specific Drug
Teratogens
• Alcohol –
defective limbs,
facial
abnormalities,
and intelligence
issues
• Nicotine –
attention and
birth weight
issues
Other Teratogens
• Blood type issues – Rh- mothers and a Rh+ fetus
might cause the mother’s immune system to
attack the fetus. A number of extremely negative
factors can occur (heart, brain, skin, and other
fatal abnormalities)
• Maternal age issues –
birth weight, mortality
rates, and down syndrome
rates increase for very
young mothers and those
over 35
Summing Things Up
• We reviewed what scientists use to determine
what we are like, and what makes us unique.
• We covered how we go from one cell to the
complex organism that we are at birth.
• We discussed some of the problems that can
occur during this growth process.
That’s it for today…
• In the next class, we begin to look at
development after birth.
• Please make sure to have read chapter 3 by the
time we get back.