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The Start of Life: Genetics


Less than 2% of ALL pregnancies produce twins! ... DIZYGOTIC Twins. 2 separate ova are fertilized by 2 separate sperm ... Twin births are up 42 % under these ... – PowerPoint PPT presentation

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Title: The Start of Life: Genetics

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 ? Zygote
  • Important things to remember about fertilization
  • Females are born with all their ova
  • Males produce several hundred million sperm daily
  • 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

More about chromosomes…
  • One pair of chromosomes is provided by the mother
    and one pair by the father
  • 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
  • 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

Basics of Genetics Continued
  • A GENOTYPE is the underlying combo of genetic
    material present in an organism
  • A PHENOTYPE is an observable trait that is
    actually seen
  • Alleles are genes for traits that may take
    alternate forms
  • Homozygous
  • Heterozygous

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.
-neither parent carries gene child cannot
develop PKU -one parent carries child cannot
develop -both parents child has 1 in 4 chance
Alleles 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
  • X-linked genes
  • Males have higher risk for x-linked disorders
  • Why?! Because they lack a 2nd X chromosome to
    counteract the genetic info that produces the

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
  • of human genes less than thought

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 areas…
  • Behavioral geneticists explore how behavioral
    difficulties may have a genetic basis (example
  • How genetic defects may be remedied
  • The inheritance patterns of genetic disorders

Behavioral Genetics Continued
  • How physically damaged genes contribute to
    genetic disorders
  • The role of spontaneous mutation in genetic
  • How environmental factors affect genetic mutation
    (x-ray exposure, teratogens)

Some genetic disorders include…
  • Down Syndrome
  • Extra chromosome on the 21st pair
  • Sickle-Cell Anemia
  • A blood disorder
  • Tay-Sachs Disease
  • Causes death before school-age
  • Klinefelters Syndrome--XXY

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 --a small sample of fetal cells
    drawn by a needle inserted into the amniotic
  • samples of hairlike material that surrounds the
  • ULTRASOUND SONOGRAPHY high-frequency sound waves
    scan the mother's womb to produce an image of the
    unborn baby whose size and shape can then be

Nature vs. Nurture… The 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?
  • Nonhuman 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

Studying Heredity
  • Human studies
  • Twin studies
  • Differences between monozygotic twins separated
    at birth
  • If monozygotic twins are more similar than
    dizygotic twins on a particular trait than we can
    assume that genetics plays a role

Studying Heredity Continued
  • Unrelated but shared environment
  • Biological parents and their children versus
    adoptive parents and their children
  • 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

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 in 3 ways!
  • Active Genotype-Environment Effects
  • Passive Genotype-Environment Effects
  • Evocative Genotype-Environment Effects

The Start of Life Genetics Prenatal Development
  • Fertilization The Moment of Conception
  • The joining of the sperm and ovum to create the
    single-celled zygote
  • 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

Some Facts About Infertility…
  • About 15 of couples suffer from infertility
  • There are several causes
  • Parental age
  • hormone imbalance
  • illicit drugs or cigarettes
  • STDs
  • stress
  • the woman's mother taking certain drugs during

How Can I Get Pregnant?
  • Having sex would be a good start!
  • 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.

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.

Psychological Effects of Alternative Pregnancies
  • 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

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 2 to 8 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
  • ectoderm
  • endoderm
  • mesoderm

(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!
Miscarriage and Abortion
  • Miscarriage or Spontaneous Abortion
  • 15 to 20 of all pregnancies end in miscarriage
  • Usually occurs in the first several months
  • Usually happens because of genetic abnormality
  • Abortion A very emotional issue
  • Effects of abortion study by APA
  • Most women feel relief after abortion but also
    feel regret and guilt sometimes severe
  • However, in most cases negative feelings did not
    last unless the woman was already experiencing
    serious psychological distress prior to the
  • Difficult choice with a lot of strong

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.

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Other threats to prenatal development…
  • A mother's diet clearly plays an important role
    in bolstering the development of the fetus.
  • Women with a diet high in nutrients are more
    likely to have fewer complications during
    pregnancy, easier labor, and healthier baby
  • Mothers over 30 and adolescents at greater risk
  • 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
  • Rubella (German measles)
  • Chicken pox and mumps may cause birth defects and
    miscarriage, respectively.
  • Syphilis and gonorrhea can be transmitted to the
  • 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 (drug given in 50s for morning
    sickness) 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 deformities
  • Fetal Alcohol Effects (FAE)

More Threats to Prenatal Development
  • Smoking reduces the oxygen content and increase
    carbon monoxide
  • Smokers are 50 more likely to have a mentally
    retarded child than non-smokers
  • Fathers can affect the prenatal environment
  • Use of drugs may affect fathers sperm and cause
    genetic consequences at conception
  • second hand smoke
  • Stress on mother is unhealthy