Science
farie20
prenataldevelopment.pptxPrenatal Development
Learning Objectives
You will learn about how we inherit genes
You will learn about the combined influence of environment and genetics on development
You will learn the stages of prenatal development
You will learn about common teratogens
Building Blocks
Gametes- reproductive cells (sperm and ovum)
Zygotes- fertilized ovum (genetic material of both gametes)
Building Blocks
Genes- 25,000 of them, our code
Dna (deoxyribonucleic acid)- makes up genes, huge molecules
46 chromosomes in 23 pairs
Gametes hold one chromosome from each pair (23 in each)
Zygote has a unique set of 46 chromosomes
Twins
Monozygotic
Dizygotic
Twins
Monozygotic- one zygote, identical twins
Dizygotic- Two zygotes, Fraternal Twins
Triplets and quadruplets can be a combination of mono and dizygotic
How do you get your sex?
In pair #23 Chromosomes are not always the same
Xx- female
Xy- male
Each ova carries an x, each sperm carries an x or y
How do you get everything else?
Lets talk about gregor mendel and his Peas
Green Peas and yellow Peas
GG+YY = yG and GY- seemed like G trait disappeared
YG +YG= YY, YG, GY, and GG- ¼ were green
What’s the deal greg?
The gene for yellow peas was dominant
The gene fore green peas was recessive
Phenotype- what you see
Genotype- what your genetic material contains
Homozygous- when both inherited genes are the same
Heterozygous- when one gene is dominant, one recessive
Common genetic disorders
Down Syndrome- extra chromosome on 21st pair
Most common cause of mental retardation
Fragile X Syndrome- caused by injured gene on x chromosome
Results in mild to moderate MR
Sickle-Cell Anemia- blood disorder common in people of African descent (also provides resistance to malaria)
Results in poor apetite, stunted growth, yellowish eyes, swollen stomach
Severe cases result in death in childhood
Common genetic disorders
Tay-sachs disease- causes blindness and muscle degeneration, leads to death in childhood
Most common among those of eastern European Jewish descent and French Canadians
Klinefelter’s syndrome- XXY males, underdeveloped genitals, very tall, large breasts
Heredity and environment
We inherit characteristics, but our parents also have those characteristics, so in a way, our genes influence our environment
Multifactorial transmission- both genetic and environmental factors determine a trait
Why can’t my family stop eating pasta?
Appearance and predisposition for diseases from parents
Pick up on behavior patterns from caregivers
So we are all socialized to eat all the time
Culture of carbs
Everyone has diabetes, high blood pressure, bad cholesterol, etc.
Intelligence
There is a genetic link
Identical twins score more similar than fraternal twins
There is an environmental link
twins raised together score more similar than twins raised apart
Identical twins raised apart still score more similar than siblings raised together
I’m going to stop harping on this point
Look in your book for lots of examples of environment + genetics
Stages of prenatal development
How to make a zygote
Step 1: sperm enters vagina
Step 2: sperm pass through cervix into the uterus
Step 3: sperm meets ovum in fallopian tube
Step 4: fertilization- one sperm enters the ovum
Germinal stage
Fertilization – 2 weeks
Zygote divides rapidly and travels to the uterus
Now we call it a blastocyst
It implants into the uterine wall
Cells begin to specialize
Embryonic stage
2 weeks – 8 weeks
Firmly attached to wall- embryo
Ectoderm- outer layer that will become hair and skin, teeth, nerves, brain, spinal cord
Mesoderm- middle layer that will become muscles, bones, blood, veins, arteries, hearth
Endoderm- inner layer which will become the digestive system, liver, pancreas, respiratory system
Head and brain rapidly growing
Fetal stage
8 weeks – birth
Sexual differentiation begins
Starts when major organs are differentiated
Limbs fully develop, kicking starts ~6 months
Brain divides into hemispheres- they can hear, sleep
Rapid changes, grows from 1 inch to a full sized baby
Teratogens
External agents (e.g. drugs, chemicals, viruses, etc.) that produce birth defects
Placenta can’t keep everything out
Remember critical periods/sensitive periods?
Teratogens
Diet- more varied diet=less complications
Avoid- fish high in mercury, raw Meat and fish, Raw Egg, soft cheese and unpasteurized dairy, Caffeine, herbal tea, alcohol, unwashed fruits and vegetables
Drug Teratogens
Cigarettes- risk of miscarriage, stillbirth, low weight, premature birth, cleft palate, SIDS, can be multigenerational
Accutane- risk for hydrocephalus, brain defects, MR, ear/face/heart/limb abnormalities, skin lesions, miscarriage
Tetracycline and Doxycycline- yellow teeth and weak bones
Drug Teratogens
Antidepressants- risk of learning difficulties, maybe withdrawal symptoms, irritability, benefits to mother may outweigh risks
Cocaine- risk of miscarriage, premature birth, detachment of placenta, low birth weight, brain damage, head and limb abnormalities, gastro-urinary abnormalities, heart defects, withdrawal in infancy
Other risks and complications
Age- risks increase with age for miscarriage, down syndrome, ectopic pregnancy,
Prenatal care/health- stress, poor care increase risks
Rubella, chicken pox, mumps- cause birth defects
Syphilis and gonorrhea can be transmitted to fetus
Aids can be passed to children if AZT isn’t taken
Other risks and complications
Fetal alcohol syndrome (FAS)- below-average intelligence/MR, growth delays, facial deformities, due to alcohol use during pregnancy
Father’s smoking during pregnancy and drug use before conception can impact health of the fetus, same with teratogens like mercury, lead, which bind to sperm
Mother’s stress as a result of father’s behavior
