The Start of Life: Genetics & Prenatal Development

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Chapter 2

• The Start of Life Genetics Prenatal Development

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What is Heredity?

• Inheritance! The transmission of qualities
  genetically derived from ones ancestors

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Genes Chromosomes The Code of Life

• Genes are the basic unit of genetic information
• Composed of DNA sequences
• DNA determines the nature of every cell in the
  body and how it will function

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(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 by the
  mother.
• One pair of chromosomes is provided by the father
  at fertilization.

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Some important things to know about multiple
births

• 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

• MONOZYGOTIC Twins
• Genetically identical form when cluster of cells
  in the ovum splits off within the first 2 weeks
  following fertilization

• DIZYGOTIC Twins
• 2 separate ova are fertilized by 2 separate
  sperm no more genetically similar than 2 siblings

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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
  expressed
• The DOMINANT TRAIT is the trait that is expressed
• The RECESSIVE TRAIT is present in the organism
  but not expressed

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(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)

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Behavioral geneticists investigate several
areas

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

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(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)

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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)

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(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.

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Some Facts About Infertility

• About 15 of couples suffer from infertility
  (inability to conceive after 12 to 18 months of
  trying)
• 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
  pregnancy

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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.

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• ? 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

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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

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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)

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Some Psychological Disorders at Least Partially
Related to Genetic Factors

• schizophrenia
• major depression
• alcoholism
• autism
• attention-deficit hyperactivity disorder

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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
  stressors

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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
  stages.

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The 3 Phases of the Prenatal Period

• GERMINAL STAGE
• the first and shortest stage of prenatal
  development
• takes place during the first two weeks following
  conception.
• 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.

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(The 3 Phases of the Prenatal Period, continued)

• The EMBRYONIC STAGE
• 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
  layers
• the ectoderm (the outer layer forming the skin,
  hair, teeth, sense organs, the brain and spinal
  cord)
• 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).

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(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
  weight.
• Organs become more differentiated and
  operational.
• By three months the fetus swallows and
  urinates.
• By four months the mother will be able to feel
  her fetus move

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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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Teratogen Sensitivity
Various parts of the body are more sensitive to
teratogens at different stages of development
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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.
• -- 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

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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.

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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.

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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

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(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
  delayed.
• Fathers can affect the prenatal environment
• (second hand smoke and the environment)