Genetics _ Prenatal Development

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					Genetics & Prenatal
  Development
       Overview of Genetics
• Chromosomes are long twisted strands
  of deoxyribonucleic acid (DNA) and are
  found in the nucleus of the cell
• Humans have 23 pairs of chromosomes
• DNA is the chemical basis of heredity
  and carries instructions
• DNA code carried on each chromosome is
  arranged in thousands of segments called
  genes.
• Genes are the basic unit of heredity
Conception
              Conception
• At conception, the genes carried on the
  23 chromosomes contributed by your
  biological mother’s ovum were paired
  with the genes carried on the 23
  chromosomes contributed by your
  biological father’s sperm, creating your
  unique genetic makeup.
• Multiple gene pairs are involved in
  directing many complex features of
  development.
         Dominant and Recessive
• Genotype—underlying genetic makeup
• Phenotype—traits that are expressed/displayed
• Dominant genes—will always be expressed if present
  – Traits such as freckles, dark eyes, dark hair, and
    dimples are referred to as dominant characteristics
    because they require only one member of a gene
    pair to be dominant for the trait to be displayed
• Recessive genes—will expressed only if paired
  with an identical recessive gene. Will not be
  expressed if paired with a dominant gene.
• We inherit from our biological parents a
  genetic potential, the expression of which can
  be influenced by environmental conditions.
Characteristic Dominant    Recessive

Eye color     Brown        Grey, blue

Hair          Dark         Light
              Curly        Straight

Hands         Extra fingers 5 fingers
              Limb dwarfing Normal limbs

Face          Broad lips   Thin lips
              Dimples      No dimples
              Sex Linked Traits
• The sex chromosomes, the 23rd pair of
  chromosomes, determine biological sex
• In females, the 23rd pair of chromosomes is made
  up of two large X chromosomes. XX
• In males, a large X chromosome and a smaller Y
  chromosome make up the 23rd pair. XY
• For males, the smaller Y chromosome often does
  not contain a corresponding gene segment to match
  the one on the X chromosome.
• This means that a male can display certain
  recessive characteristics as the result of having
  only one recessive gene carried on the X
  chromosome of his XY pair.
• Traits determined by recessive genes on the X
  chromosomes are referred to as sex-linked
    Physical and Psychological
     Development Related
• Physical development begins at
  conception
• Physical maturity sets limits on
  psychological ability
  – visual system not fully functional at birth
  – language system not functional until much later
• Prenatal environment can have lifetime
  influence on health and intellectual ability
Prenatal and
 Childhood
Development
         Prenatal Development
• Prenatal defined as “before birth”
• Prenatal stage begins at conception and ends
  with the birth of the child.
• At conception, chromosomes from the
  biological mother and father combine to
  form a single cell—the fertilized egg, or
  zygote.
• The prenatal stage has three distinct
  phases:
     1. germinal period,
     2. embryonic period,
        Prenatal Development
• Conception—when a sperm penetrates the
  ovum
• Zygote—a fertilized egg
• Germinal period—first two weeks after
  conception
• Embryonic period—weeks three through
  eight after conception
• Fetal period—two months after conception
  until birth
From Conception to Zygote
                Zygote
• A newly fertilized egg
• The first two weeks are a period of
  rapid cell division.
• Attaches to the mother’s uterine wall
• At the end of 14 days becomes a
  cluster of cells called an
  embryo.
                    Embryo
• Developing human from about 14 days until the
  end of the eighth week
• Time of rapid growth and intensive cell
  differentiation
• Most of the major organs are formed during this
  time.
• Genes on the sex chromosomes and
  hormonal influences trigger the initial
  development of the sex organs
• At the end of the eighth week the fetal period
  begins.
               Embryo
• The embryo is protectively housed
  in the fluid-filled amniotic sac; the
  embryo’s lifeline is the umbilical
  cord.
• Via the umbilical cord, the embryo
  receives nutrients, oxygen, and
  water and gets rid of carbon
  monoxide and other wastes
                 Placenta
• A cushion of cells in the mother by which
  the fetus receives oxygen and nutrition
• Acts as a filter to screen out substances
  that could harm the fetus
• The umbilical cord attaches the embryo
  to the placenta, a disk-shaped tissue on
  the mother’s uterine wall.
• The placenta prevents the mother’s
  blood from mingling with that of the
  developing embryo, acting as a filter to
  prevent some, but not all, harmful
  substances that might be present in the
  mother’s blood from reaching the
  embryo
Prenatal Development
                Fetal Period
• The period between the beginning of the ninth
  week until birth
  1. By the end of the third month, the fetus can
     move its arms, legs, mouth, and head
  2. During the fourth month, the mother
     experiences quickening—she can feel the
     fetus moving.
  3. By the fifth month, the fetus has distinct
     sleep–wake cycles and
     periods of activity.
  4. During the sixth month, the fetus’s brain
     activity becomes similar to that of a
     newborn baby.
  5. During the final two months, the fetus will
Prenatal Development – 45 Days
Prenatal Development – 2
         months
          Prenatal Influences
           on Development
•   Nutrition
•   Anxiety
•   Mother’s general health
•   Maternal age
•   Teratogens—any agent that causes
    a birth defect (e.g., drugs, radiation,
    viruses)
                Teratogens
• Substances that pass through the placenta’s
  screen and prevent the fetus from developing
  normally
• Teratogens include:
  – Exposure to radiation
  – Diseases, such as rubella, syphilis, genital
    herpes, and AIDS
  – Toxic industrial chemicals, such as
    mercury and PCBs
  – Drugs taken by the mother, such as
    alcohol, nicotine, cocaine, and heroin
      Prenatal Development
• Play “Teratogens and Their Effects on
  the Developing Brain and Mind”
  (12:44) Segment #12 from The Mind:
  Psychology Teaching Modules (2nd
  edition)
Smoking and Birth Weight
   Fetal Alcohol Syndrome
– cluster of defects occurring in infants
  born to mothers that drink heavily
  during pregnancy
– leading cause of mental retardation
– can be totally prevented by abstaining
  from alcohol during pregnancy
  Prenatal Brain Development
• Play “The Effects of Hormones and
  the Environment on Brain
  Development” (6:50) Module #2 from
  The Brain: Teaching Modules (2nd
  edition)

				
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