Problem 1 – Genetics and early development
What is cell division?
Somatic cells → for repair and growth
Gametes → reproduction and its variety
How do we all have unique DNAs?
Meiosis: process of cell division into gamete production, diploid → haploid
• Divides twice Meiosis I and Meiosis II:
Meiosis Num. chromosomes Num. chromatids Haploid/diploid
I 46 →46 46→92→46 Diploid →diploid
II 46→23 46→23 Diploid → haploid
Variety insured by:
• Homologous chromosomes lining up by chance (not maternal on one side and paternal on the other →
mixed up)
• Fertilization – combination of two random gametes
o each gamete has unique combination of half of the DNA → chances of 223 (2 possible chromosomes
in each pair of 23 unique chromosomes meet) = 8,388,608 (probability that a woman would produce
the same egg without crossing over being included), and that is only the possibility of one gamete
• Crossing over: occurs in homologous chromosomes during meiosis I → non-sister chromatids of homologous
chromosomes trade segments of genes
How is genetic material present in the body and how is it passed on?
In the nucleus → chromosomes → DNA → genes → alleles → sequences of base pairs
• DNA usually free in the nucleus, when cell divides → coils into chromosomes
• Homologous chromosomes: same genes but not always the same alleles
• Homozygous: 2 identical alleles of a gene (AA)
• Heterozygous: 2 different alleles of a gene (Aa)
• Diploid and haploid: diploid are all somatic cells (2n), haploid are gamete (n)
Codominance – two heterozygous alleles are equally powerful → phenotype fully and equally expressed e.g. blood-
type AB
Polygenic traits – characteristics influenced by many genes not a single one e.g. weight, height, intelligence, skin
color
What types of chromosomal abnormalities are there and how do they
develop?
- Most abnormalities are lethal and will fail to develop or spontaneously abort
- Some are not lethal → 1 in 250 children has a chromosomal abnormality
Chromosomal abnormalities
1. Too many or too few – if meiosis or mitosis does not proceed well
2. Broken or damaged chromosomes
3. Sex or autosomal chromosomes
Sex chromosomes:
• Involve the 23rd pair = sex chromosomes
, • Turner’s syndrome (X0) – sterile, females but need more estrogen to look womanly, struggles with spatial
and verbal abilities
• Poly-X “superfemale” (XXX, XXXX or XXXXX) – female and fertile, somewhat below average intelligence,
developmental delays and intellectual problems the more X chromosomes
• Klinefelter’s syndrome (XXY or XXXY) – sterile male with some secondary sex characteristics of a female,
taller than XY males, intellectual problems the more X chromosomes
• Supermale syndrome (XYY, XYYY, XYYYY) – typically fertile, phenotypic males who are taller, and develop
more acne, intellectual characteristics similar to normal XY male
➔ Problems in meiosis (mostly anaphase), wrong attachment of spindle
➔ X chromosome is larger thus is more harm when there are more than 2 present (too much genetic
information being produced)
Autosomes:
• Problems with the 22 non-sex chromosomes
• Most commonly happens when an gamete carries an extra autosomal chromosome and combines with a
normal one = 47 chromosomes
o 3 chromosomes of one type =trisomy
o Most common = Down syndrome = trisomy-21
o Chromosome 21 is the smallest, trisomy’s of other chromosomes usually lead to death
• Down syndrome – trisomy-21
o Mentally retarded
o Average IQ around 55
o Congenital eye, ear, and heart defects
o Physiological features: almond eyes, protruding tongue, short stubby limbs, flattened nose
o Developmental progress is the greatest when they are included, with lots of emotional support
Genetic abnormalities
• Most genetic problems are recessive traits – does not appear unless both of the parents carry the harmful
allele and a child inherits it from each
• Sex-linked defects are more common in males because the alleles are often on the X-chromosome which he
inherits from the mother and only owns one (if it is defected, does not have an extra X that could be healthy
as females do)
• E.g. colorblindness = X-linked
• Sickle-cell anemia = 2 recessive alleles
• Dominant allele → the parent will display the disability e.g. Huntington’s disease (nervous system
degenerates but often displays late in life once the person already has children)
• Mutations – change the genetical information into harmful, non-harmful, beneficial or fatal
o Occurs spontaneously
o Can be induced by environmental hazards – toxic waste, radiation, chemicals etc.
What types of environmental factors influence child development and
when? (based on the pictures in the problem)
Teratogens – environmental factors that may cause developmental deviations (most threatening in the embryonic
stage)
• Medications
• Drugs
• Environmental toxins
• Other factors: age, diet, emotional state affect the response of the mother to the teratogens
How teratogens exert effects on prenatal development
1. A teratogen exerts its effects largely during critical periods of development
, a. Embryonic stage
b. Each organ has a more specific period e.g. heart → 20-40 days after conception
2. Teratogens have specific effects → different teratogens influence different developmental processes
3. Maternal or fetal genotypes may counteract a teratogen’s effect (their vulnerability to a specific one or not)
4. Effects of one teratogen may intensify effect of another
a. Mothers physiological status, nutritional and hormonal balance modify the impact of a teratogen
b. E.g. nutritional deficiencies intensify effects of drugs ingested by the mother
5. Different teratogens may produce the same defect
6. The longer and the more intensely a fetus is exposed to a teratogen, the more likely it is to be harmed
Legal and illegal drugs
• Heavy use of Aspirin → low birth weight, lower IQ, and poor motor control
• Too much Caffeine → higher risk of miscarriage, low-birth-weight infants
• Smoking → disturbance in placental functioning
o changes in maternal physiology which leads to oxygen deprivation
o changes in fetal brain
• Nicotine and alcohol
o lower birth weight
o more prenatal growth deficiencies for mothers that do both than those that only use one substance
o Sudden infant death syndrome SIDS – more common in mothers who smoke, drink or take narcotics
during pregnancy
• Passive smoke
o Low birth weight (when e.g. father smokes)
o Can delay intellectual and behavioral development
o Increased risk for various illnesses
• Alcohol
o Fetal alcohol syndrome (FAS) – stunned growth, physiological abnormalities, mental retardation
o Facial, heart and limb defects
o 20% shorter than average children
o Mental retardation – mainly because of lack of oxygen
▪ Only 0,3 ml of vodka can stop respiratory actions of the fetus for more than half an hour
o Damage from alcohol is greatest in the last trimester
o Men who drink excessively may sustain genetic damage that leads to defects in their offspring
• FAS
o Children with FAS may be excessively irritable, distractible, hyperactive
o May repeatedly bang their heads or rhythmically rock their bodies
o Slow in turning head or suckling
o Lower IQ
• Cocaine
o Brian hemorrhages (bleeding), neuron damage
o Children → irritable, higher pitched prolonged crying, depressed, unresponsive behavior
• Addicted mother
o Offspring also addicted to this drug
o Following birth babies undergo withdrawal symptoms
▪ Irritability, minimal ability to control arousal, trembling, shrill crying, rapid respiration,
hyperactivity
▪ These symptoms can be so severe, they result in death in the first few days of life
o If the mother stops taking the drug in the 3rd trimester, the infant is less likely to be affected
o May contribute to problematic attachment relationship formation
▪ Infants not as alert and may not maintain visual or physical contact
Environmental toxins
• Radiation, lead, mercury, herbicides, pesticides, household cleaners, food additives, cosmetics
, • Automobile exhaust fuels, contaminated drinking water, lead-based paint
• Prematurity
• Low birth weight
• Brian damage
• Problems in cognitive and intellectual functioning
• PCB contaminated fish
o Babies were smaller, weighed less, less responsive, neurologically advanced
o Lower IQ, memory, higher impulsivity
o PCB in breast milk
• Fathers exposure to environmental toxins → chromosomal abnormalities
Medical interventions in pregnancy and childbirth
• Diethylstilbestrol – to prevent miscarriage → caused vaginal abnormalities, cancer of cervix and risk of
breast cancer in the female offspring
• Thalidomide – anti-anxiety, anti-nausea drug → children born with abnormalities of face, fusing fingers,
malformation of heart etc.
o Available only for treatment of cancer, AIDS etc.
Parental factors
• Age and parity (how many children the mother had)
o Under 15 and over 35 → experience more problems
o Older women more difficulty conceiving (by 40 it is less than 5%)
o Chances of miscarriage and chromosomal abnormality increases with age
o Emerging health risks of mothers such as hypertension, diabetes, alcoholism increases with age, it
not the age per se
o Higher age of the father also causes more birth defects
o Too young women → unhealthy habits
o Usually connected to SES
• Diet
o Deficiencies in vitamins, minerals, and proteins
o Increased risk of miscarriage
o Lower social and motor development, cognitive abilities
o Supplements of folic acid daily in the last 2 months of pregnancy reduce the risks of premature birth
• Emotional state
o Mother’s emotionality can lead to metabolic and biochemical changes
▪ Stress
▪ Anxiousness
o Fetuses more active in the uterus
o Hyperactive infants, irritable, tend to cry more, feeding and sleep problems
o At the age of 7 more likely to be depressed and anxious
o More likely to develop schizophrenia
• Diseases and disorders
o Rh factor incompatibility – mother’s blood produces antibodies that attack the fetal blood cells →
death of fetus
▪ Less likely in first time mothers
o Hypertension (high blood pressure) and diabetes → underdeveloped immune system
o Genital herpes – one of the most harmful viruses
▪ Can cause blindness, motor abnormalities, mental retardation, neurological disorders
▪ 60% babies die, 90% survive with serious problems
o HIV and AIDS
▪ 25% chance that the mother transmits it to child, however greater if she breastfeeds
▪ If use of drug therapy and Caesarean delivery → rate of transmission reduced to 1%
, What are the stages of pregnancy? (what happens in what stage?)
Germinal stage – zygote
• First 2 weeks of life from fertilization
• Rapid cell division
• Implants itself in the wall of the uterus
• From this point on the zygotes becomes dependent on the mother
• Until this point, alcohol, drugs etc. won’t harm the organism
Embryonic stage – embryo
• 3rd – 8th week of gestation (carrying of the embryo/fetus)
• Development of
o Amniotic sac (filled with amniotic fluid which serves as a protective buffer against physical shock and
temperature changes)
o Placenta – transfers O2 and nutrients, removes CO2, does not permit direct blood exchange –
however some drugs, viruses and antibodies are able to pass to the embryo
o Umbilical cord – transmits between placenta and embryo
• Inner mass differentiates into
o Endoderm becomes – gastrointestinal tract, trachea, bronchi, glands, and vital organs (lungs,
pancreas, liver)
o Mesoderm – muscles, skeleton, circulatory and excretory systems, and inner skin layer
o Ectoderm – sensory cells, nervous system (and skin, nails, hair, teeth…)
• 4th week → head begins to take shape, eyes, nose and mouth
o Blood vessels that will become the heart start to pulsate
• 5 week → buds that will become limbs start to form
th
• End of embryonic stage – 8th week (10th of pregnancy)
o Face, fingers, toes, external genitalia
o Most common miscarriages often unnoticed (1 in 4 pregnancies)
Development in directions
- Cephalocaudal: development starts at the brain and proceeds down to trunk and legs (from head to tail)
- Proximal-distal: development from center to more distant areas (from middle out)
The fetus
• From 3rd month of gestation to delivery
• Development of muscles and the nervous system
• By the 3rd month the fetus has all its body parts including organs and external genitalia
• 4th months – starts moving
• 5 months – reflexes (suckling, swallowing, hiccupping)
• Develops nails, sweat glands, more adult-like skin
• 6 months – eyes open and close
• Age of viability (22-26 weeks → app. 6 months)
o Point at which the fetus has physically advanced systems to survive even if born prematurely
(reasonable chances not 100%)
o However, can have difficulties mainly depending on the environmental conditions
