Biological Beginnings

Psych 125Human Development

Christopher GadeOffice: 1031-G

Office hours: Tu 12-1:30 and by apt.Email: gadecj@gmail.com

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 transferredto every cell replicated from thisfirst 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 witheach of our parents, but makes it sowe’re never exact replicas of ourparents

– 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

b bB bB bB B

b

B

Blond hair

Brown hair

How brown-haired parents

can have a blond-haired

child: the gene for blond hair is

recessiveMother

B bFather

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 cellsthat will eventually develop intothe embryo

– Trophoblasts – outer layer of cellsthat later provide nutrients andsupport for the cell

• Implantation – the attachment ofthe zygote to the uterine wall of afemale – 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

Brain Development at this Stage

• Neural tube, a collection of cells that will form the brain and nervous system develop during 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 movingand formation of nervous systemstructures• 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 TrimesterPoint 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 high-risk

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, butminimal 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, mortalityrates, and down syndromerates increase for veryyoung mothers and thoseover 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.