GENETIC FOUNDATIONS
Why are we the way we are?
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Genotype
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Heredity supplies our genotype (genetic makeup).
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Phenotype
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Heredity and environment combine to form the phenotype
(observable characteristics).
The Genetic Code
Chromosomes
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Store and transmit genetic information
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Each cell in the human body contains 23
pairs.
DNA:
Deoxyribonucleic Acid
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DNA molecules make up chromosomes.
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Code for transmission of all genetic
information
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A gene is a segment of a DNA
molecule.
The Sex Cells
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Gametes
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Sperm and Ova
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Contains 23 chromosomes (normal body cells
contain 46 chromosomes)
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Sperm and Ovum unite to form zygote
Male or Female?
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Chromosome Pairs
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The 22 pairs of matching
chromosomes within a human cell are called autosomes.
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The 23rd pair are sex
chromosomes.
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Females have an XX pair.
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Males have an XY pair.
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Sex is determined by whether
an X-bearing or a Y-bearing sperm fertilizes the ovum.
Multiple Births
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Fraternal or dizygotic
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Two separate ova are fertilized by two separate sperm.
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Identical or monozygotic
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A single zygote separates into two clusters of cells that develop
into two individuals.
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Monozygotic twins have the same genetic makeup.
Multiple Births
Patterns of Genetic Inheritance
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Two forms of each gene occur at the same place on the autosomes, one
from the mother and one from the father.
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If the genes are alike, the child is homozygous and will
display the inherited trait.
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If they are different, then the child is heterozygous, and
relationships between the genes determine the trait that will appear.
Patterns of Genetic Inheritance
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Dominant-recessive inheritance: Only
one heterozygous gene's influence is exhibited.
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The dominant gene is expressed.
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A heterozygous individual can pass on a recessive gene.
Patterns of Genetic Inheritance
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Mutation
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A sudden and permanent change in a DNA
segment takes place, by chance or as a result of substances in the
environment.
Patterns of Genetic Inheritance
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X-linked inheritance
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A recessive gene is carried on the X chromosome.
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Males are more likely to be affected.
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The Y chromosome is not as long as the X and may not have a
corresponding dominant gene.
Chromosomal Abnormalities
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Occur mostly during meiosis –
production of ova and sperm cells.
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Involve more DNA than
single-gene disorders, so they often produce disorders with many mental and
physical symptoms.
Down Syndrome
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Cause
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21st pair of chromosomes contains extra chromosome
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Symptoms
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Distinct physical features, mental retardation, speech problems, and
slow motor development
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Incidence
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Increases with maternal age
PRENATAL ENVIRONMENTAL
INFLUENCES
Teratogens
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Environmental agent that causes damage during the prenatal period
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The genetic makeup of the mother and developing organism may enable
or hinder their ability to withstand harm.
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The presence of several negative factors at once can worsen the
impact.
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The effects vary with the organism's age at time of exposure.
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Especially vulnerable during a period of rapid development
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The embryonic period is when serious defects are most likely to
occur, since the foundations for all body parts are being laid down.
Prescription and Nonprescription Drugs
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Thalidomide, a sedative used in the 1960s
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Caused severe limb
deformations in embryos
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Diethylstilbestrol (DES) was widely prescribed between 1945 and 1970
to prevent miscarriages.
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Babies seemed unharmed at
birth; problems with reproductive systems sometimes appeared later.
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Aspirin
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Linked to low birth weight,
infant death around the time of birth, poorer motor development, and lower
intelligence scores in early childhood
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Heavy caffeine intake
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Linked to prematurity,
miscarriage, and newborn withdrawal symptoms, such as irritability and
vomiting
Illegal Drugs
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Mothers who use cocaine, heroin, or methadone during pregnancy may
have babies who are born drug-addicted.
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Babies who are prenatally exposed to cocaine may have genital,
urinary tract, kidney, and heart deformities, as well as brain seizures.
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Fathers may contribute to these negative effects as cocaine may
attach itself to sperm and cause birth defects.
Tobacco
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Effects include low birth weight and increased chances of prematurity,
miscarriage, and infant death.
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Nicotine causes the placenta to grow abnormally; the transfer of
nutrients is reduced, and the fetus gains weight poorly.
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Raises concentrations of carbon monoxide in bloodstreams of both
mother and fetus
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Stopping smoking can help the baby, even in the third trimester.
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Passive smoking is related to low-birth-weight, infant death, and
possible long-term impairments in attention and learning.
Alcohol
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Fetal alcohol syndrome (FAS)
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Defects occur when women consume a lot of alcohol during pregnancy;
mental retardation, slow physical growth, and facial abnormalities.
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Fetal alcohol effects (FAE)
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Condition of children who display some, but not all, of the defects
of FAS. Usually the mother drank less.
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FAS babies fail to catch up later in physical size.
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Mental impairment is permanent.
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Alcohol requires large quantities of oxygen to metabolize, which is
drawn away from the developing embryo or fetus.
Radiation
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Radiation exposure can cause
miscarriage, slow physical growth, an underdeveloped brain, and
malformations of the skeleton and eyes.
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Low-level radiation can
increase the risk of childhood cancer.
Environmental Pollution
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Mercury
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Mental retardation, abnormal
speech, difficulty in chewing and swallowing, and uncoordinated movements
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Lead
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Prematurity, low birth weight,
brain damage, and a wide variety of physical defects
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Polychlorinated-biphenyls
(PCBs)
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Lower than average birth
weight, smaller heads (possible brain damage) and less interest in
surroundings
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Memory and learning
difficulties later in development
Infectious Disease
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Rubella (three-day or German measles)
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Many abnormalities during the
embryonic period
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Acquired immune deficiency syndrome (AIDS)
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20 to 30% of women pass the
virus to the developing organism.
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Herpes viruses
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Developing organism is
especially sensitive.
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Toxoplasmosis
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Parasitic disease caused by
eating undercooked or raw meat or by contact with the feces of infected cats
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During the first trimester, it
leads to eye and brain damage.
Other Maternal Factors
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Nutrition
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Malnourished babies who die reveal fewer brain cells, a lower brain
weight, and abnormal brain organization.
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Prenatal malnutrition can damage the immune system and the structure
of the pancreas, liver, and blood vessels.
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Successful intervention after birth must not only provide nutrients,
but must also deal with mother-baby interactions.
Emotional Stress During
Pregnancy
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Intense stress is associated
with a higher miscarriage rate, prematurity, low birth weight, respiratory
illness, and physical defects.
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When mother experiences fear
and anxiety, blood supply increases to the brain, heart, and limbs resulting
in decreased blood supply to the uterus. Stress hormones also cross the
placenta.
Rh Blood Incompatibility
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The Rh factor is a protein
that, when present in the fetus's blood but not in the mother's, can cause
the mother to build up antibodies that can return to the fetus's system and
destroy red blood cells.
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Rh blood incompatibility can
result in mental retardation, miscarriage, heart muscle damage, and infant
death.
Maternal Age and Previous
Births
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In the thirties or forties
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Increased risk of infertility,
miscarriage, and chromosomal defects
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Women without serious health
difficulties in their forties do not experience more prenatal problems than
those in their twenties.
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In the teenage years
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A teenager's body is
physically capable of supporting pregnancy.
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But problems arise when
adolescents do not have access to medical care or are afraid to seek it.
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No relationship has been found between number of previous births and
prenatal problems.
Importance of Prenatal Health
Care
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Regular prenatal checkups help ensure the health of the mother and
fetus.
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Toxemia
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In the last half of pregnancy, the mother's blood pressure increases
and face, hands, and feet swell. If untreated, it can cause convulsions in
the mother and death of the fetus.
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Lack of health insurance, psychological stress, demands of taking
care of other young children, lack of transportation, ambivalence about the
pregnancy, and family crises can deter mothers from obtaining prenatal care.
Prenatal Diagnosis and Fetal
Medicine
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Detection of problems using
procedures such as amniocentesis, chorionic villus sampling, ultrasound, and
maternal blood analysis
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Some problems can be treated
before birth, but practices are controversial.
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Today, the goal is to map
chromosomes and correct hereditary defects with genetic repair or
replacement.
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