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The Start of Life: Genetics & Prenatal Development


Chapter 2 The Start of Life: Genetics & Prenatal Development What is Heredity? Inheritance! – PowerPoint PPT presentation

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Title: The Start of Life: Genetics & Prenatal Development

Chapter 2
  • The Start of Life Genetics Prenatal Development

What is Heredity?
  • Inheritance! The transmission of qualities
    genetically derived from ones ancestors
  • As humans, we begin life as a single cell!
  • (1/20,000,000th of an ounce!)

This single cell is transformed into something
resembling a person by the human genetic code!
  • How is the human genetic code transferred??
  • The sex cells from the mother and father that
    form a new cell at conception (also known as
    sperm and ovum)

  • Fertilization is the process by which a sperm and
    an ovum (the gametes) join go form a single new
    cell, called a zygote
  • Some important things to remember about
  • Females are born with all their ova (about 400,
    000! the ova mature only when the female reaches
    puberty an ovum ripens every 28 days)
  • Males produce several hundred million sperm
  • Fertilization typically takes place in the
    fallopian tubes

Genes Chromosomes The Code of Life
  • Genes are the basic unit of genetic information
  • Composed of DNA (deoxyribonucleic acid) sequences
  • DNA determines the nature of every cell in the
    body and how it will function

(More about genes)
  • Humans have over 100, 000 genes!
  • They are arranged in specific locations and in a
    specific order along 46 chromosomes
  • (chromosomes are rod-shaped sections of DNA
    organized into 23 pairs)

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Some more things to know about chromosomes
  • One pair of chromosomes is provided (through the
    gametes) by the mother
  • One pair of chromosomes is provided by the father
    at fertilization
  • Gametes (sperm ova) are formed by a process
    called meiosis
  • ALL other cells replicate the genetic code by a
    process called mitosis

Some important things to know about multiple
  • Less than 2 of ALL pregnancies produce twins!!
    (the odds are even slimmer for triplets,
    quadruplets, etc.!)

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A Comparison of Twins
  • Genetically identical form when cluster of cells
    in the ovum splits off within the first 2 weeks
    following fertilization
  • 2 separate ova are fertilized by 2 separate
    sperm no more genetically similar than 2 siblings

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Other kinds of multiple births
  • Triplets, quadruplets, etc. can be either
    monozygotic or dizygotic
  • The use of fertility drugs increases the chance
    of having multiple births
  • 1 in 10 that the birth will be dizygotic
  • Twin births are up 42 under these
  • Racial Ethnic differences affect the rate of
    multiple births
  • African American 1 out of 70 births are
  • Caucasians 1 out of 86 dizygotic
  • Chinese Americans 1 out of 300 dizgotic

Some important facts
  • The 23rd chromosome determines the sex of the
  • Females are XX
  • Males are XY
  • The FATHERs sperm determines the sex of the

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The Basics of Genetics
  • Gregor Mendel
  • Worked with peas discovered that when 2
    competing traits were present, only one could be
  • The DOMINANT TRAIT is the trait that is expressed
  • The RECESSIVE TRAIT is present in the organism
    but not expressed

(More basics of genetics)
  • A GENOTYPE is the underlying combo of genetic
    material present (but not outwardly visible) in
    an organism
  • A PHENOTYPE is an observable trait that is
    actually seen physical appearance
  • -Alleles are genes for traits that may take
    alternate forms (example hair texture/color,
    skin tone)
  • Homozygous (inheriting similar genes for a given
    trait )
  • Heterozygous (inheriting different forms of a
    gene for a given trait)

Alleles (genes for traits that make take
alternate forms) continued
  • A recessive allele from each parent ?the child
    displays the recessive characteristic
  • A dominant allele received from each parent ? a
    dominant characteristic is displayed
  • MOST traits are the result of POLYGENIC
    INHERITANCE (a combo of multiple gene pairs leads
    to a particular trait)

  • Some genes are neither dominant nor recessive,
    but instead are a combination
  • AB blood type
  • Some are x-linked genes
  • Located on the x chromosome
  • Males have higher risk for x-linked disorders
  • Why?! Because the lack a 2nd X chromosome to
    counteract the genetic info that produces the
  • examples of x-linked disorders red-green color
    blindness, hemophilia

PKU is an inherited disorder in which a child is
unable to use an essential amino acid, and allows
a build up of toxins causing brain damage and
mental retardation. We can see the transmission
of genetic information in humans by considering
the transmission of this disorder.
-neither parent carries gene child cannot
develop PKU -one parent carries child cannot
develop -both parents child has 1 in 4 chance
The MOST recent approach to the study of the
effects of heredity on behavior development
  • Behavioral Genetics

The Human Genome Project
  • In early 2001 molecular biologists succeeded in
    mapping the sequence of genes on chromosomes
  • -one of the most important moments in the
    history of genetics!
  • -already leading to important advances in our
    understanding of genetics
  • -99.9 of gene sequence is shared by all
    humans similarities of people realized!
  • of human genes less than thought (30,000 rather
    than 100,000)
  • Will also help id disorders

Uniquely Human?
The human genome project has lead to the
realization that humans are less complex than
originally thought, and not much different that
some primitive species!
Behavioral geneticists investigate several
  • Behavioral geneticists explore how behavioral
    difficulties may have a genetic basis (example
  • How genetic defects may be remedied
  • The inheritance patterns of genetic disorders

(the focus of behavioral geneticists continued)
  • How physically damaged genes contribute to
    genetic disorders
  • The role of spontaneous mutation in genetic
    disorders (how genes sometimes change form on
    their own)
  • How environmental factors affect genetic mutation
    (x-ray exposure, teratogens)

Some genetic disorders include
  • Down Syndrome
  • A disorder produced by the presence of an extra
    chromosome on the 21st chromosome pair
  • Sickle-Cell Anemia
  • A blood disorder (named for the shape of the
    disordered blood cells)

(More genetic disorders include)
  • Tay-Sachs Disease
  • An untreatable disorder produces blindness,
    muscle degeneration prior to death
  • Klinefelters Syndrome
  • -- Results from the presence of an extra X
    chromosome that produces underdeveloped genitals,
    extreme height, and enlarged breasts.

Inheriting Hemophilia
Hemophilia is a blood-clotting disorder that has
been an inherited problem in the royal families
of Europe, as illustrated above in the
descendants of Queen Victoria of Britain.
What is Genetic Counseling??
  • The discipline that focuses on helping people
    deal with issues related to inherited disorders
  • Blood, skin, urine often used to isolate/examine
    specific chromosomes
  • -- Possible genetic defects can be identified by
    assembling a karyotype, a chart containing
    enlarged photos of each of the chromosomes.

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Other tests that can take place once a woman is
  • AMNIOCENTESIS (the process of identifying genetic
    defects by examining a small sample of fetal
    cells drawn by a needle inserted into the
    amniotic fluid surrounding the unborn fetus).
    find genetic defects that involves taking samples
    of hairlike material that surrounds the embryo).
  • ULTRASOUND SONOGRAPHY (a process in which
    high-frequency sound waves scan the mother's womb
    to produce an image of the unborn baby whose size
    and shape can then be assessed).

Some Facts About Infertility
  • About 15 of couples suffer from infertility
    (inability to conceive after 12 to 18 months of
  • There are several causes
  • Parental age
  • Previous use of birth control pills, illicit
    drugs or cigarettes, STDs
  • men who have an abnormally low sperm count
  • the woman's mother taking certain drugs during

Several Alternate Routes to Pregnancy
  • -- ARTIFICIAL INSEMINATION (fertilization that
    occurs after a man's sperm is placed directly
    into a woman's vagina by a physician).
  • -- IN VITRO FERTILIZATION (IVF) (a procedure in
    which a woman's ova are removed from her ovaries,
    and a man's sperm are used to fertilize the ova
    in a laboratory).
  • -- SURROGATE MOTHER, a woman who agrees to carry
    the child to term, may be used in cases where the
    mother is unable to conceive.

  • ? Evidence suggests that the quality of parenting
    in families who have used artificial means to
    conception may even be superior to naturally
    conceived children.
  • ? The psychological adjustment of children
    conceived artificially is no different than that
    of children conceived using natural techniques

Nature vs. NurtureThe interaction of heredity
vs environment
  • The correct question is not whether behavior is
    caused by nature or nurture but how much by
    nature and how much by nurture

Possible Causes of Intelligence Nature vs.
Intelligence may be explained by a range of
possible causes, spanning the nature-nurture
continuum. Which explanation do you find most
convincing, based on information in this chapter?
How do scientists investigate the effects of
heredity environment on development anyway??
  • Nonhumans studies
  • - Laboratory animals
  • bred to share genetic backgrounds and placed
    in different environments to explore the effects
    of these environments.
  • conversely, they use genetically different
    animals in similar environments to determine the

(How scientists investigate the effects of
heredity environment, continued)
  • Human studies
  • ? Human twins used to study the effects of genes
    and the environment.
  • ? Differences between monozygotic twins separated
    at birth (usually most likely but not always due
    to different environments).
  • ? If monozygotic twins are more similar than
    dizygotic twins on a particular trait than we can
    assume that genetics plays a role.

(Human studies in heredity/environment research,
  • ? People who are unrelated but share the same
    environment also tell us about environmental
  • ? Researchers also study biological parents and
    their children versus adoptive parents and their
    children to see the effects of heredity versus
  • ? Bottom line Virtually all traits,
    characteristics, and behaviors are the joint
    result of the combination and interaction of
    nature and nurture.

No issue looking at the influence of heredity and
environment has more research than the topic of
intelligence, because it is a core human
The closer the genetic link between two
individuals, the more similar their IQ scores are
More about the interaction of heredity
environment in effecting development
  • --The more genetically similar two people are,
    the more likely they are to share physical
    characteristics (e.g., height, weight).
  • --Genetics plays a significant role in
    intelligence however, the environment is also a
    significant factor.
  • --Increasing evidence supports the conclusion
    that at least some personality traits have at
    least some genetic components. Some personality
    characteristics have been found to be linked to
    genetic factors (neuroticism, extroversion)

Genetic Environmental Influences On Personality
  • Increasing evidence supports the conclusion that
    at least some personality characteristics are
    affected by genetic factors
  • Neuroticism (emotional reactivity)
  • Extroversion (outgoing/sociability)
  • How do we know which personality traits reflect
  • Examination of genes
  • Twin studies

Inheriting personality traits
These personality traits have been found to have
genetic components. The higher the percentage,
the greater the influence of heredity.
Some Psychological Disorders at Least Partially
Related to Genetic Factors
  • schizophrenia
  • major depression
  • alcoholism
  • autism
  • attention-deficit hyperactivity disorder

The psychological disorder of schizophrenia has
clear genetic components. The closer the genetic
link, the more likely a relative is to develop
Psychological Disorders Predisposition or
Automatic Inheritance?
  • Genetics alone does not automatically lead to the
    development of schizophrenia or other
    psychological disorders.
  • If genetics were the sole cause, identical twins
    would automatically develop schizophrenia, and
    this is not the case!
  • Other factors contribute, including structural
    abnormalities, biochemical imbalances, and

Can Genes Influence Environments?
  • Developmental psychologist Sandra Scarr says
    yesgenetics can influence environment!
  • 3 ways
  • 1. Active genotype-environment effects (kids
    focus on aspects of the environment that are
    congruent with their genetic abilities)
  • Noticing the music tryouts flyer over the sports
    tryout flyer

(Sandra Scarr, genetics environment continued)
  • 2. Passive genotype-environment effects (parents
    genes are associated with environment where kids
    are raised)
  • Parents are sports oriented more opportunities
    for kids in this area
  • 3. Evocative genotype-environment effects (kids
    genes elicit a type of environment
  • Kid with athletic ability draws attention to this
    so parents will nurture

The Start of Life Genetics Prenatal
Developmental Development
  • Fertilization The Moment of Conception
  • The joining of the sperm and ovum to create the
    single-celled zygote that develops into a baby
  • Females are born with 400,000 ova, which mature
    at puberty
  • Males produce sperm with a much shorter lifespan!
    Several hundred million sperm per day in adult

Anatomy of the Sex Organs
Routes to Pregnancy
  • Sexual Activity
  • During sexual activity, the sperm released wind
    their way to the ovum. One sperm fertilizes an
    ovum, and together contain all the genetic data
    to produce a new human.
  • Artificial insemination (sperm placed in vagina
    by physician)
  • In vitro fertilization (ova removed and
    fertilized by sperm in a lab)
  • Surrogate Mother (another woman carries a
    couples baby)

Prenatal Growth Change
The Stages of the Prenatal Period The Onset
of Development
  • Developmentalists divide the prenatal period into
    three phases the germinal, embryonic, and fetal

The 3 Phases of the Prenatal Period
  • the first and shortest stage of prenatal
  • takes place during the first two weeks following
  • characterized by methodical cell division and the
    attachment of the organism (blastocyst) to the
    wall of the uterus.
  • The baby is called a zygote at this stage.

(The 3 Phases of the Prenatal Period, continued)
  • the period from two to eight weeks following
    fertilization during which significant growth
    occurs in the major organs and body systems.
  • At this point the child is called an embryo.
  • The developing child is now composed of three
  • the ectoderm (the outer layer forming the skin,
    hair, teeth, sense organs, the brain and spinal
  • the endoderm (the inner layer producing the
    digestive system, liver, pancreas, and
    respiratory system)
  • the mesoderm (sandwiched between the inner and
    outer layers and forms the muscles, bones, blood,
    and circulatory system).

(The 3 Phases of the Prenatal Period, continued)
  • 3) The FETAL STAGE begins about eight weeks after
    conception and continues until birth.
  • The developing child from eight weeks after
    conception until birth is called a FETUS.
  • The fetus dramatically increases in size and
  • Organs become more differentiated and
  • By three months the fetus swallows and
  • By four months the mother will be able to feel
    her fetus move

During the fetal period, the proportions of the
body change dramatically!
Threats to Prenatal Development
  • Certain aspects of mothers' and fathers'
    behavior, both before and after conception, can
    produce lifelong consequences for the child.
  • ? TERATOGENs (environmental agents such as a
    virus, chemical, or other factor that produces a
    birth defect. )
  • -- At some phases of prenatal development, a
    teratogen may have minimal impact at other
    periods, consequences can be severe.

Teratogen Sensitivity
Various parts of the body are more sensitive to
teratogens at different stages of development
Other threats to prenatal development
  • -- A mother's diet clearly plays an important
    role in bolstering the development of the fetus.
  • -- Research shows that mothers over 30 and
    adolescent mothers are at greater risk for a
    variety of pregnancy and birth complications
  • premature birth
  • low birth weight
  • Down syndrome
  • higher infant mortality rates
  • Illness

Other threats to prenatal development
  • ? Illness in a pregnant woman can have
    devastating consequences
  • - Rubella (German measles) prior to the 11th
    week can cause blindness, deafness, heart
    defects, or brain damage.
  • - Chicken pox and mumps may cause birth defects
    and miscarriage, respectively.
  • - Syphilis and gonorrhea can be transmitted to
    the child.
  • - Babies born with AIDS can have birth
    abnormalities including small, misshapen faces,
    protruding lips, and brain deterioration. 90
    percent have neurological delays and deficits in
    motor coordination, speech, and facial
    expression. In addition, they are susceptible to
    infection. Survival past infancy is rare.

More threats to prenatal development
  • ? Mother's use of legal and illegal drugs pose
    serious risks to the unborn child
  • - aspirin can lead to bleeding
  • -thalidomide caused missing limbs
  • -marijuana restricts oxygen to the fetus
  • -cocaine restricts blood flow and oxygen, babies
    are born addicted and go through withdrawal they
    are shorter and weigh less they have serious
    respiratory problems and birth defects or
    seizures it is often impossible to soothe them.

Still more threats to prenatal development
  • Both alcohol and cigarettes can disrupt the
    development of the fetus
  • -just two drinks a day has been associated with
    lower intelligence
  • FETAL ALCOHOL SYNDROME (FAS) is a disorder
    caused by the pregnant mother consuming
    substantial quantities of alcohol during
    pregnancy potentially resulting in mental
    retardation, delayed growth, and facial

(threats to prenatal development)
  • --smoking reduces the oxygen content and increase
    carbon monoxide babies can miscarry or are born
    with abnormally low birth weight babies born to
    smokers are shorter and may be intellectually
  • Fathers can affect the prenatal environment
  • (second hand smoke and the environment)

  • Dont forget to read chapter 3 for next time!!!!!