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Heredity and Prenatal Development


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Title: Heredity and Prenatal Development

  • Heredity and Prenatal Development

The Influence of Heredity on Development
Chromosomes and Genes
  • Genetics - the field of biology that studies
  • Fundamental in the transmission of physical
  • Also plays a role in psychological traits
  • Chromosomes Rod-shaped structures composed of
    genes that are found within the nuclei of cells
  • Gene The basic unit of heredity. Composed of
  • Polygenic Resulting from many genes
  • Deoxyribonucleic Acid (DNA) Genetic material
    that takes the form of a double helix composed of
    phosphates, sugars and bases.

  • Life begins as a single cell or zygote that
    divides repeatedly.
  • Mitosis
  • Genetic code carried into new cells in our bodies
  • DNA breaks apart double helix duplicates
  • DNA forms two camps on either side of the cell,
    and then the cell divides

Fig. 2-1, p. 24
Fig. 2-2, p. 25
  • Sperm and ova are produced through meiosis or
    reduction division.
  • 46 chromosomes within the cell nucleus first line
    up into 23 pairs.
  • DNA ladders unzip, leaving unpaired halves of
    chromosome when cell divides, one member of each
    pair goes to each newly formed cell.
  • Each new cell nucleus contains only 23
    chromosomes, not 46.

Fig. 2-3, p. 25
Identical and Fraternal Twins
  • Monozygotic (MZ)
  • - Zygote divides into two cells that separate
    so that each
  • develops into an individual with the same
    genetic makeup.
  • Dizygotic (DZ)
  • - Two ova are produced in the same month, each
    fertilized by a different sperm cell.
  • Ovulation
  • - As women reach end of childbearing years,
    ovulation becomes less regular.
  • -Results in months when more than one ovum is

Dominant and Recessive Traits
  • Traits determined by pairs of genes
  • each member of pairs of genes termed an allele
  • Homozygous
  • having two identical alleles
  • Heterozygous
  • having two different alleles
  • Incomplete dominance/codominances
  • when both alleles are shown
  • Dominant trait
  • trait that is expressed
  • Recessive trait
  • trait that is not expressed when genes have been
    paired with dominant genes
  • Carriers
  • people who bear one dominant gene and one
    recessive trait

Fig. 2-4, p. 26
Table 2-1, p. 27
Chromosomal and Genetic Abnormalities
  • Down syndrome
  • Caused by an extra chromosome of the 21st pair,
    resulting in 47 chromosomes
  • Characteristic features
  • -rounded face
  • -protruding tongue
  • -broad, flat nose
  • -sloping fold of skin over the inner corners of
    the eyes
  • Show deficits in cognitive development and motor

Fig. 2-5, p. 28
Sex-Linked Chromosomal Abnormalities
  • 1 male in 700-1,000 has XYY
  • leads to heightened male secondary sex
  • most individuals with disorder are infertile
  • 1 male in 500 has Klinefelter syndrome (XXY)
  • leads to inadequate development of male primary
    and secondary sex characteristics
  • 1 female in 2,500 has a single X resulting in
    Turner Syndrome
  • poorly developed ovaries, short, and infertile.
  • 1 female in 1,000 has XXX sex chromosomal
    structure called Triple X syndrome
  • normal in appearance but tend to show
    lower-than-average language skills and poorer
    memory for recent events

Klinefelter Syndrome (XXY)
  • 1 male in 500
  • Caused by extra X on sex chromosome
  • Produces less testosterone than normal males
  • Characteristic features of testes, deepening of
    voice, musculature, and male pattern of body hair
    do not develop properly
  • Typically treated with testosterone replacement

Turner Syndrome (X)
  • 1 female in 2,500
  • Single X chromosome
  • External genitals are normal, ovaries poorly
    developed, producing little estrogen
  • Shorter than average and infertile
  • Cognitive deficits with low estrogen problems
    with visual-spatial skills, mathematics, and
    nonverbal memory

Triple X Syndrome (XXX)
  • 1 female in 1,000
  • Appears normal, but demonstrates
    lower-than-average language skills
  • Poorer memory for recent events
  • Development of external sex organs appears normal
  • Increased incidence of infertility

Phenylketonuria (PKU)
  • Enzyme disorder transmitted by a recessive gene
    affecting 1 child in 8,000
  • Cannot metabolize an amino acid called
    phenylalanine builds up in body and impairs
    functioning of the central nervous system (CNS)
  • Results are mental retardation, psychological
    disorders, physical problems
  • No cure, but children can be placed on diets low
    in phenylalanine and develop normally

Huntingtons Disease (HD)
  • Affects 1 in 18,000 Americans
  • Fatal, progressive degenerative disorder
  • Dominant trait
  • Physical symptoms include uncontrollable muscle
  • Psychological symptoms include loss of
    intellectual functioning and personality change
  • Onset of HD is delayed until middle adulthood
  • Possibly half their offspring will develop it
  • Medicines can deal with some symptoms

Sickle-Cell Anemia
  • Carriers
  • -1 in 10 African Americans
  • -1 in 20 Latino or Latina Americans
  • Caused by a recessive gene
  • Red blood cells take on the shape of a sickle and
    clump together, obstructing small blood vessels
    and decreasing the oxygen supply
  • Lessened oxygen can impair cognitive skills
  • Physical problems
  • -painful and swollen joints
  • -jaundice
  • -potentially fatal conditions such as
    pneumonia, stroke, and heart and kidney failure

Tay-Sachs Disease
  • 1 in 30 Jewish Americans are carriers
  • Caused by recessive gene
  • Causes the central nervous system to degenerate,
    resulting in death
  • Commonly found among children in Jewish families
    of Eastern European background

Cystic Fibrosis
  • Approx. 30,000 Americans have disorder, 10
    million more are carriers (1 in 31 people)
  • Caused by recessive gene
  • Most common fatal hereditary disease among
  • Children suffer from excessive production of
    thick mucus that clogs the pancreas and lungs
  • Most victims die of respiratory infections in
    their 20s

Sex-Linked Genetic Abnormalities
  • Genetic defects only carried on the X sex
  • Hemophilia genetic disorder in which blood does
    not clot properly
  • Duchenne muscular dystrophy sex linked
  • Involve recessive genes
  • Females with two X sex chromosomes are less
    likely than males to show sex-linked disorder
  • Sons of female carriers are more likely to be

Genetic Counseling and Prenatal Testing
  • Genetic counselors compile information about a
    couples genetic heritage to explore if their
    children will have a genetic abnormality.
  • Couples with likelihood of passing on genetic
    abnormality tend to adopt or not have children of
    their own.
  • Prenatal testing can indicate if the embryo or
    fetus is carrying genetic abnormalities.

  • Performed on mother 14-16 weeks after conception
  • Syringe withdraws fluid from the amniotic sac
    contains cells sloughed off by fetus
  • Cells separated, grown in culture, and examined
    for genetic and chromosomal abnormalities
  • Routine for women over 35 to detect for Down
    syndrome other chromosomal abnormalities
    increase dramatically as women approach 40
  • Amniocentesis carries some risk of miscarriage.

Fig. 2-6, p. 30
Chorionic Villus Sampling
  • Carried out between 9th and 12th week of
  • Syringe inserted through vagina into uterus to
    suck out threadlike projections (villi) from the
    outer membrane that covers the amniotic sac and
  • Results available in days
  • CVS slightly greater risk than amniocentesis of
    miscarriage both increase the risk of miscarriage

  • Sound waves that are too high in frequency to be
    heard by human ear obtain information about the
  • Ultrasound waves are reflected by the fetus
    computer uses the information to generate a
    picture of the fetus
  • Picture is termed a sonogram
  • Used to guide the syringe in amniocentesis and
    CVS by determining the position of the fetus
  • Used to track growth of fetus, detect multiple
    pregnancies, detect structural abnormalities

Blood Tests
  • Used to identify sickle-cell anemia, Tay-Sachs
    disease, and cystic fibrosis
  • Alpha-fetoprotein (AFP) used to detect neural
    tube defects such as spina bifida and chromosomal
  • Neural tube defects cause elevation in the AFP
    level in the mothers blood
  • Elevated AFP levels related to increased risk of
    fetal death

Heredity and the Environment
Heredity and Environment
  • Inheritance, nutrition, learning, exercise,
    accident, and illness contribute to development
    of traits
  • Genotypes
  • -Set of traits we inherit from our parents
  • Phenotypes
  • -Actual set of traits
  • -Both genetic and environmental influences

Kinship Studies
  • The more closely people are related, more genes
    they have in common
  • Parents and children have 50 genetic overlap
  • Siblings have 50 genetic overlap
  • Aunts, uncles have 25 overlap with nieces and
    nephews grandparents, 25 overlap with
  • First cousins have 12.5 overlap

Twin Studies
  • Monozygotic (MZ) twins share 100 of genes
  • -MZ twins resemble each other more closely than
    DZ twins on a number of physical and
    psychological traits.
  • -MZ twins more likely to look alike and be
    similar in height
  • -MZ twins more likely to share autism,
    depression, schizophrenia, and vulnerability to
  • Dizygotic (DZ) twins share 50 of genes same as
    other siblings

Adoption Studies
  • Children that are separated from their natural
    parents at an early age and reared by adoptive
    parents provide special opportunities for sorting
    out nature and nurture.
  • When children who are reared by adoptive parents
    are nonetheless more similar to their natural
    parents in a trait, a powerful argument is made
    for a genetic role in the appearance of that

Conception Against All Odds
  • Conception refers to the union of an ovum and a
    sperm cell.
  • Ova
  • Women born with all the ova they will ever have,
    about 400,000
  • Released from ovarian follicle and enter
    fallopian tube 3-4 days later, egg propelled by
    small, hairlike structures called cilia, and
    perhaps, by contractions in the wall of the tube
  • If egg not fertilized, discharged through the
    uterus and vagina, along with endometrium that
    had formed to support an embryo, in the menstrual
    flow during reproductive years, about 400 ova
    will ripen and be released

Conception (contd)
  • Ova are larger than sperm, barely visible to the
  • Sperm cells develop through stages sperm with Y
    sex chromosomes swim faster than sperm with X sex
  • Male fetuses suffer a higher rate of miscarriage
    than females, often during the first month of
  • 150 million sperm ejaculated, only 1 in 1,000 can
    approach an ovum

Conception (contd)
  • Sperm have to fight vaginal acidity, gravity, and
    swim against current fluid coming from the
  • If sperm survive, reach fallopian tubes 60-90
    minutes after ejaculation approximately 2,000
    enter the correct tube
  • Sperm are egged on by a change in calcium ions
    that occurs when an ovum is released.
  • Only one enters have to thin the gelatinous
    layer of egg secrete an enzyme that briefly
    thins layer
  • Once sperm enters, layer thickens and locks out
    other sperm

Conception (contd)
  • Chromosomes from the sperm cell line up across
    from corresponding chromosomes in the egg cell.
  • Form 23 new pairs with unique set of genetic
  • The direction that sperm travel is guided by a
    change in calcium ions that occurs when an ovum
    is released.

Fig. 2-8, p. 33
Fig. 2-9, p. 34
  • Infertility problems with men
  • - Low sperm count (most common)
  • - Lack of sperm
  • - Genetic factors
  • - Environmental poisons
  • - Diabetes
  • - Sexually transmitted infections
  • - Overheating of the testes
  • - Pressure (e.g., bike seats)
  • - Aging
  • - Certain prescription and illicit drugs

Infertility (contd)
  • Infertility problems with women
  • - Irregular ovulation, lack of ovulation
  • - Irregularities among the hormones that govern
  • ovulation, stress, and malnutrition
  • - Pelvic inflammatory disorder (PID)
  • -infection that scars the fallopian tubes and
    other organs,
  • impeding the passage of sperm
  • -Endometriosis
  • -can obstruct the fallopian tubes

Infertility Options
  • Artificial insemination
  • -Sperm is collected and quick-frozen
  • -Sperm then injected into womans uterus at
    time of ovulation
  • addresses low sperm count as well as low
    sperm motility
  • -Can be used for a woman to get pregnant who
    does not have a partner
  • In vitro fertilization
  • -Ripened ova are surgically removed from the
    mother and
  • placed in laboratory dish fathers sperm also
    placed in dish
  • -One or more ova fertilized and injected into
    mothers uterus to become implanted
  • -Used when fallopian tubes are blocked or
    father has low sperm motility
  • -A donor can be used

Infertility Options (contd)
  • Donor IVF
  • -Mother does not produce ova
  • -Ovum from another woman is fertilized and
    injected into the
  • uterus of the mother-to-be
  • Surrogate mothers
  • -Mothers who bring baby to term for other women
    who are
  • infertile
  • -Can be artificially inseminated by partner of
    infertile woman
  • Adoption
  • -Another way for people to obtain children that
    results in the
  • formation of loving new families

Preimplantation Genetic Diagnosis (PGD)
  • Reliable method for selecting the sex of the
    child prior to implantation
  • Ova are fertilized in vitro
  • After a few days of cell division, cell is
    extracted from each
  • Sex chromosomal structure of the cell is examined
    microscopically to determine its sex
  • Embryos of desired sex are implanted in the
    womans uterus

Prenatal Development
Prenatal Development
  • Normal gestation period 280 days from date of
    fertilization 266 days
  • Divided into three periods
  • 1. Germinal stage (Weeks 0 - 2)
  • 2. Embryonic stage (Weeks 3 - 8)
  • 3. Fetal stage (Weeks 9 - Birth)

The Germinal Stage
  • The period from conception to implantation
  • Blastocyst
  • -Cells separate into groups that will become
    different structures
  • -Inner part of blastocyst has two distinct
    layers that form a thickened mass of cells called
    embryonic disk
  • -These cells eventually become the fetus
  • Trophoblast
  • Four membranes that will protect and nourish the
  • 1. One produces blood cells, then it
  • 2. One develops into umbilical cord and blood
    vessels of the
  • placenta
  • 3. One develops into the amniotic sac
  • 4. One becomes the chorion, which will line
    the placenta

The Embryonic Stage
  • Development follows cephalocaudal (head to tail)
    and proximodistal (near to far).
  • Growth of the head takes precedence over growth
    of the lower parts of the body.
  • Relatively early maturation of the brain and
    organs that lie near the spine
  • Ectoderm
  • -Outer layer of cells
  • -Develops into nervous system, sensory organs,
    nails, hair,
  • teeth, and outer layer of skin
  • Endoderm
  • -Forms digestive and respiratory system, liver,
    and pancreas
  • Mesoderm
  • -Develops into excretory, reproductive, and
    circulatory systems, muscles, the skeleton,
    and the inner layer of skin

The Embryonic Stage (contd)
  • Head and blood vessels form third week after
  • Heart starts beating
  • Major organ systems develop within first 2 months
  • -Arm buds and legs appear by end of 1st month
  • -Eyes, ears, nose, and mouth take shape
  • -Nervous system and brain begins to develop
  • During 2nd month, nervous system begins to send
  • Embryo is 1 inch long and weighs 1/30th of an
  • Teeth buds are formed by end of stage

The Embryonic Stage (contd)
  • At 5-6 weeks, internal and external genitals
    resemble primitive female structures.
  • By 7th week, genetic code asserts itself, causing
    sex organs to differentiate
  • Genetic activity on Y sex chromosome causes the
    testes to begin to differentiate.
  • Ovaries begin to differentiate if the Y
    chromosome is absent.
  • Androgens begin to produce.
  • Embryo and fetus develop within protective
    amniotic sac sac is surrounded by clear membrane
    and contains amniotic fluid

The Embryonic Stage (contd)
  • Amniotic fluid acts as natural air bag allowing
    embryo and fetus to move without injury.
  • Placenta is a mass of tissue that permits the
    embryo to exchange nutrients and waste with the
  • Mother and embryo have separate circulatory
  • Placenta permits oxygen and nutrients to reach
    the embryo from the mother, and permits carbon
    dioxide and waste products to pass to the mother
    from the embryo.

The Embryonic Stage (contd)
  • Mother eliminates waste through her lungs and
  • Drugs such as aspirin, narcotics, alcohol,
    tranquilizers, and others cross the placenta and
    affect the fetus.
  • Placenta secretes hormones that preserve
    pregnancy, prepare breasts for nursing, and
    stimulate contractions.
  • Placenta passes from the birth canal after the
    baby, hence the term afterbirth.

The Fetal Stage
  • Lasts from beginning of third month until birth
  • Between 9th and 10th, week fetus responds to
    external stimulation
  • Major organ systems formed at end of first
  • Second trimester consists of further maturation
    and gain in size
  • Weight advances from 1 ounce to 2 pounds and
    grows from about 3 to 14 inches

The Fetal Stage (contd)
  • Fetus can open and shut eyes, suck thumb at end
    of second trimester
  • Gains about 5 1/2 pounds and doubles in length
  • By 7th month, fetus turns upside down toward
  • Doubles in weight by end of 7th month
  • 90 survival if born at end of 7th month and
    given quality care

The Fetal Stage (contd)
  • By 13th week, fetus responds to sound waves
  • Experiment by DeCasper and Fifer (1980)
    demonstrated that a fetus is learning while in
  • Fetal movements are noticeable during middle of
    4th month
  • At 29-30 weeks, fetus moves limbs vigorously and
    turns summersaults
  • Fetus gets cramped as it grows, becomes less
    active during 9th month

Fig. 2-12, p. 41
Environmental Influences on Prenatal Development
  • Maternal malnutrition effects
  • -low birth weight
  • -prematurity
  • -retardation of brain development
  • -cognitive deficiencies
  • -behavioral problems
  • -cardiovascular disease
  • Fetal malnutrition can sometimes be overcome by a
    supportive, care-giving environment.
  • Supplementing diets of pregnant women shows
    positive effects on motor development of infants.
  • Maternal obesity linked with higher risk of

Environmental Influences on Prenatal Development
  • Women should gain between 25-35 pounds
  • -Overweight women may gain less
  • -Slender women may gain more
  • Teratogens
  • -Environmental agents can harm the embryo or
  • -Includes drugs taken by mother, lead, mercury
  • Pathogens
  • -Disease-causing organisms
  • -Bacteria and viruses

Environmental Influences on Prenatal Development
  • Critical periods refer to the times when organs
    are developing.
  • Particular teratogens at a particular time can be
    harmful to the fetus.
  • Sexually transmitted infections such as syphilis
    and HIV/AIDS can affect the development of the
  • -Routine blood tests are given early in
    pregnancy to diagnose syphilis

Environmental Influences on Prenatal Development
  • Rubella
  • -Women affected by rubella (German measles)
    during first 20 weeks of pregnancy stand 20
    chance of bearing children with birth defects
    such as deafness, mental retardation, heart
    disease, eye problems (including blindness)
  • Preeclampsia (or Toxemia)
  • -Life-threatening characterized by high blood
    pressure that may afflict women late in 2nd
    trimester or early in 3rd trimester
  • Rh incompatibility
  • -Consists of antibodies produced by the mother
    and transmitted to a fetus or newborn infant that
    cause brain damage or death

Drugs Taken by the Parents
  • Thalidomide
  • -A sedative used for treatment of insomnia and
  • -Causes missing or stunted limbs during second
    month of pregnancy

Drugs Taken by the Parents (contd)
  • Hormones
  • -Women at risk for miscarriages have been
    prescribed hormones to help maintain their
  • -Progestin
  • -Synthetic version of naturally occurring
  • -Can masculinize the external sex organs
    of female embryos
  • -Diethylstilbestrol (DES)
  • -Used to prevent miscarriage during 1940s
    and 1950s
  • -Caused cervical and testicular cancer in
    some offspring
  • -1 in 1,000 daughters of DES users will
    develop cancer in the reproductive
  • tract

Drugs Taken by the Parents (contd)
  • High doses of vitamins A and D
  • -Associated with central nervous system damage,
    small head size, and heart defects
  • Narcotics (heroine, methadone) easily pass
    placental membrane and cause fetuses to become
  • -After birth, drug is substituted so serious
    withdrawal symptoms are minimized
  • -Addicted newborns may have behavioral effects,
  • motoric delays, language delays

Drugs Taken by the Parents (contd)
  • Marijuana
  • Contributes to slower fetal growth, low birth
  • Babies of women who regularly used marijuana show
    increased tremors and startling, suggesting
    immature development of the nervous system.
  • Study by Goldschmidt et al. (2000) indicates
    prenatal exposure to marijuana can result in
  • -increased hyperactivity
  • -impulsivity
  • -problems paying attention
  • -increased delinquency and aggressive behavior

Drugs Taken by the Parents (contd)
  • Cocaine
  • Cocaine use during pregnancy increases risk of
    stillbirth, low birth weight, and birth defects.
  • Infants are excitable, irritable, or lethargic
    sleep is disturbed
  • Suggestions of delays in cognitive development
    even at 12 months of age
  • Prenatal exposure linked to lower receptive and
    expressive language abilities at older ages

Drugs Taken by the Parents (contd)
  • Alcohol
  • Heavy alcohol consumption during pregnancy can
    result in fetal alcohol syndrome (FAS).
  • FAS babies
  • -often smaller, with smaller brains
  • -facial features include widely spaced eyes,
    underdeveloped upper jaw, flattened nose
  • Psychological characteristics appear to reflect
    dysfunction of the brain.
  • Maladaptive behaviors such as poor judgment,
    distractibility, and difficulty perceiving social
    cues are common.

Fig. 2-13, p. 44
Drugs Taken by the Parents (contd)
  • Caffeine
  • Research regarding caffeine consumption is
  • -Several studies have found that pregnant women
    who take in a good deal of caffeine are more
    likely than nonusers to have a miscarriage or a
    low-birth-weight baby.

Drugs Taken by the Parents (contd)
  • Cigarettes
  • Consist of nicotine, carbon monoxide, and
    hydrocarbons (tars)
  • -Nicotine and carbon monoxide pass through
    placenta and reach the fetus
  • -Nicotine stimulates the fetus long-term
    effects unknown
  • -Carbon monoxide decreases amount of oxygen
    available to the fetus
  • -Connected with impaired motor development
    academic delays, learning disabilities, mental
    retardation, and hyperactivity
  • Smokers babies likely to be smaller than those
    of nonsmokers
  • -Babies of smokers more likely to be stillborn
    or to
  • die soon after birth
  • Men who smoke are more likely to produce abnormal
  • -Babies of fathers who smoke have higher rates
    of birth defects, infant mortality, lower
    birth weights, and cardiovascular problems.

Environmental Hazards
  • Environmental hazards consist of heavy metals
    such as lead, mercury, and zinc.
  • Exposure to lead related to delayed mental
    development at 1 and 2 years of age
  • Consumption of PCB-contaminated fish from Lake
    Michigan resulted in babies that were smaller and
    showed poorer motor functioning and memory
  • Exposure to radiation has been linked to mental
    retardation and physical deformity suggestion to
    avoid unnecessary x-rays

Parents Age
  • Older fathers more likely to produce abnormal
  • 20s ideal age for women to bear children
  • Teenage pregnancy can result in higher incidence
    of infant mortality and low birth weight.
  • Stillborn or preterm babies increase as age of
    mother increases adequate prenatal care
    decreases this likelihood even for first-time
    older mothers.