Chp.2 - Conception, Hereditary, and Prenatal Development Flashcards
What are Environment Correlations?
- processes by which genetic factors contribute to variations in the environment
3 types:
1) Passive Genotype-environment Correlation
- Occurs when children passively inherit genes and the environment provided by their family
- Ie. Being athletically inclined runs in families. Children inherit both the genes that enable success and given environmental encouragement to engage in athletics
2) Evocative Genotype-environment Correlation
- How the social environment reacts to individuals based on their inherited characteristics
- Ie. someone being more outgoing or shy will affect how they are treated by others
3) Active-Genotype Correlation:
- Occurs when individuals seek environment that support their genetic tendencies
What are Recessive disorders (homozygous)?
- the individual inherits a gene from both parents. If the gene is inherited from just 1 parent, the person is a carrier and does not have the condition
Examples of Recessive disorders?
1) Sickle Cell Disease
- RBC’s are shaped like a sickle (letter C) and affect the ability of blood to transport oxygen
2) Cystic Fibrosis
- Effects breathing and digestion due to thick and sticky mucus building up in the lungs and digestive system
3) Phenylketonuria
- Metabolic disorder
- Individual can not metabolize phenylalanine (an amino acid)
- If left untreated, intellectual deficits can occur
- Easily detected and treated with a special diet
4) Tay Sachs Disease
- Caused by enzyme deficiency resulting in accumulation of lipids in nerve cells of the brain
- Result: progressive damage to cells and decrease in cognitive and physical development
- Death occurs by age 5
5) Albinism
- Lacks melanin and processes little to no pigment in the skin, hair, and eyes
- Vision problems can occur
Examples of Autosomal Dominant Disorders (Heterozygous):
- to have the disorder, the individual only needs the gene from 1 parent
1) Huntington Disease
- Affects child’s nervous system
- Nerve cells become damaged causing parts of the brain to deteriorate
- Affects movement, behaviour, and cognition
- Fatal and occurs at midlife
2) Tourette Syndrome
- Results in uncontrollable motor and vocal tics and body jerking
3) Achondroplasia
- Uncommon form of disproportionate short stature
- Abnormal bone growth resulting in short satire, short arms and legs, large fingers, a large head, and specific facial features
What are Sex-Linked Disorders?
- when the X chromosome carries the mutated gene, the disorders is X-linked
- Males are more affected because they only have 1 X that can not be counteracted by another X
1) Fragile X Syndrome
- When the body can not make enough protein it needs for the brain to grow
- Problems with learning and behaviour occur
- Caused from an abnormality of the X chromosome (it breaks)
If a female has a fragile X, her 2nd X usually is healthy, but males with fragile X don’t have a second healthy X Chromosome.
- This is why symptoms are more serious in males.
2) Hemophilia
Problems in blood clotting
Causes internal and external bleeding
3) Duchenne muscular Dystrophy
- Weakening of muscles
- Results in inability to move, muscle wasting, and possibly death
Autosomal Chromosome Disorders:
1) Down Syndrome/Trisomy 21
- Extra chromosome 21
- Effects: intellectual disability, characteristic facial features, heart defects, other health problems
- Severity varies
2) Trisomy 9 Mosaicism
- Extra chromosome 9 in some cells
- Effects: fetal growth restriction resulting in low birth weight, facial, cardiac, musculoskeletal, genital, kidney, and respiratory abnormalities
3) Trisomy 13
- Extra chromosome 13
- Effects: multiple birth defects and die within the 1st weeks/months of life
4) Trisomy 18
- Extra chromosome 18
- Effects: multiple birth defects and early death
Sex-Linked Chromosomal Disorders
- when the abnormality is on the 23rd pair. Happens when a person has less or more than 2 sex chromosomes
1) Turner Syndrome (XO)
- Caused when all or part of 1 of the chromosomes is lost before or soon after conception due to random event
- Resulting zygote: XO composition
- Affects cognitive function and sexual maturation in girls
- Can cause infertility and short stature
2) Klinefelter Syndrome (XXY)
- When extra x chromosome is present in cells of a male due to a random event
- Y chromosome stimulates growth of male genitalia, but additional X chromosomes inhibit development
- Male might have breast development, infertility, low levels of testosterone
3) XYY Syndrome
- When an extra Y chromosome is present in cells of a male
- Effects: being taller than average, acne, increased risk of learning problems
- Has normal fertility
4) Triple X Syndrome (XXX)
- When an extra chromosome is in the cells of a female
- Effects: being taller than average, learning difficulties, decreased muscle tone, seizures, kidney problems
Germinal Period
- 14 days: lasts from conception to implantation of the fertilized egg
- Once a single sperm enters the egg wall, the wall become hard to prevent other sperm from entering
- After the sperm has entered the egg, the tail of the sperm breaks off and the head (containing genetic information) unites with the nucleus of the egg
- The sperm gets fertilized in the top section of the fallopian tube
- Zygote - cell containing combined genetic material from both parents
- During this time, the organism divides through mitosis
- After 5 days, there are 100 cells blastocyst
- Blastocysts contains an inner and outer group of cells
- Inner: embryonic disk becomes the embryo
- Outer: trophoblast, becomes the support system that nourishes the developing organism
- This stage ends when the blastocyst implants itself into the uterine wall
- Few zygotes survive beyond the 1st 2 weeks of mitosis because:
Egg and sperm do not join properly (their genetic material does not combine) - There is too little or damaged genetic material
- The zygote does not replicate
- The blastocyst does not implant into uterine wall
The Embryonic Period
- Begins the 3rd week the blastocysts is implanted in the uterine wall
- Upon implementation, blood vessels form to grow the placenta
- Placenta: structure connected to the uterus that provides nourishment and oxygen from the mother to the developing embryo via the umbilical cord
- Growth occurs in 2 different directions:
1. Cephalocaudal development - from head to tail
2. Proximodistal development - from midline outward - Structures nearest the head develop before those near the feet and structures near the torso develop before those away from the center of the body (ie. hands and fingers)
- The head develops in week 4
- In early stages, gills and a tail is present, but by the end of this stage they disappear
20% of organisms fail during this period due to chromosomal abnormalities - This period is when the organism is most vulnerable to damage if exposed to harmful substances
The fetal period
- Fetus: from 9th week-birth
Month 3: the fetus has all body parts - In the following weeks, the fetus develops hair, nails, teeth, excretory and digestive systems
Month 4-6: te eyes become more sensitive to light and hearing develops
Month 5: respiratory system develops, reflexes (ie. sucking, swallowing, and hiccuping) develop, cycles of sleep and wakefulness
Month 6: 1st chance of survival outside the womb (known as age of viability)
- Fetus can feel pain
Month 7–9: exercising its muscles and its lungs begin to expand and contract.
Month 8: layer of fat develops under the skin - serves as insulation and helps regulate body temperature after birth.
Week 37: all of the fetus’s organ systems are developed enough that it could survive outside the mother’s uterus without many of the risks associated with premature birth
Week 40: fetus continues to grow and gain weight until it hits 40 weeks
Twins
Monozygotic (identical) twins:
- occur when a fertilized egg splits apart in the first 2 weeks of development
- Result: 2 separate, but genetically identical offspring
they possess the same genotype and often the same phenotype
Zygotic (fraternal) twins: 2 eggs or ova are released and fertilized by 2 separate sperm
- They share the same amount of genetic material as would any two children from the same mother and father
- possess a different genotype and phenotype
- Older mothers are more likely to have dizygotic twins
- Couples who use fertility drugs are also more likely to give birth to dizygotic twins
Factors that influence risk problems during the first 3 months of development.
1) Timing of exposure:
- Body structures are most vulnerable to damage when they are forming
- If a substance is introduced during a particular structure’s time of development, the damage to that structure may be greater
- Ie. At 6 weeks, the ears and arms reach their critical period. If the embryo is exposed to certain substances during this period, the arms and ears may be malformed
2) Amount of exposure
Some substances are only harmful at a certain amount
The critical level depends on the size and metabolism of the mother
3) # of teratogens
- Fetuses exposed to multiple teratogens typically have more problems than those exposed to only 1
4) Genetics
- Genetic makeup impacts the affect a teratogen may have
- Genetic makeup of mother also has an effect; some mothers may be more resistant to teratogenic effects than others
5) Being male or female
- Males are more likely to experience damage due to teratogens than females
4 Categories of Teratogens
1) Physical Teratogens
- saunas, hot tubs, or infections that raise a pregnant woman’s body temperature to 102 degrees Fahrenheit or higher
- associated with neural tube defects, spontaneous abortions, and cardiovascular abnormalities
2) Metabolic Conditions affecting Pregnant Females
- Metabolic conditions: abnormalities in the chemical process of producing energy from food, and thereby affect the development and function of the body.
- Ie. malnutrition, diabetes, and thyroid disorders.
3) Infections
Rubella virus, herpes simplex virus, and syphilis can cause congenital abnormalities in fetuses
4) Drugs and chemicals Effects if based on specific agent, amount of exposure, and timing
- Includes: radiation, heavy metals (including lead), insecticides and herbicides, prescription and over the counter drugs, illicit and recreational drugs, alcohol, cigarettes, nicotine, caffeine, and even some vitamins.
Drugs as Teratogens
1) Caffeine
- Moderate amounts (200mg/12oz) are safe
- Studies show a link between higher amounts of caffeine and miscarriage and preterm birth
2) Tobacco
- Tobacco use is associated with low birth weight, placenta previa, preterm delivery, fetal growth restriction, sudden infant death syndrome, cleft lip or palate, and later health problems (ie. high bp and diabetes)
3) Alcohol
- No safe amount
- Alcohol slows down the baby’s growth, affect the baby’s brain, and cause birth defects, and may results in fetal alcohol spectrum disorder
- Children born with severe form of FASD can have abnormal facial features, severe learning disabilities, behavioral problems, and other problems
4) Cocaine
- Associated with low birth weight, stillbirths, spontaneous abortion, placental abruption, premature birth, miscarriage, and neonatal abstinence syndrome (fetal addiction causes newborn to experience withdrawal)
5) Marijuana
- No amount is safe
- Heavy use is associated with brain damage, premature birth, and stillbirth
6) Heroin
- Can cause birth defects, placental abruption, premature birth, low birthweight, neonatal abstinence syndrome, still birth, and sudden infant death syndrome
7) Over the counter medication
Some are safe
Others cause health problems
8) Prescription Drugs
Some cause birth defects that change the shape or function of one or more parts of the body that can affect overall health
9) Herbal or dietary supplements
Little is known
- Some herbs that are safe in small amounts as food might be harmful when used in large amounts as medicines
Environmental teratogens
1) Lead
Exposure to high levels of lead before and during pregnancy can lead to high bp, problems with fetal brain and nervous system development, premature birth, low birthweight, and miscarriage
2) Mercury
Exposure to mercury in the womb can cause brain damage and hearing and vision problems
3) Radiation
Exposure to radiation during pregnancy (especially bw 2 and 18 weeks) can slow growth, cause birth defects, affect brain development, cause cancer, and cause miscarriage
4) Solvents
Include degreasers, paint thinners, stain and varnish removers, paints
Maternal inhalation of solvents can cause miscarriage, slow fetal growth, premature birth, and birth defects
