Genetics

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Genetics Prenatal Development
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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

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Conception
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Conception

• At conception, the genes carried on the 23
  chromosomes contributed by your biological
  mothers ovum were paired with the genes carried
  on the 23 chromosomes contributed by your
  biological fathers sperm, creating your unique
  genetic makeup.
• Multiple gene pairs are involved in directing
  many complex features of development.

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Dominant and Recessive

• Genotypeunderlying genetic makeup
• Phenotypetraits that are expressed/displayed
• Dominant geneswill 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 geneswill 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.

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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
  recessive characteristics
• Color blindness, baldness, hemophilia, Fragile X

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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

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Prenatal and Childhood Development
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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
  cellthe fertilized egg, or zygote.
• The prenatal stage has three distinct phases
• germinal period,
• embryonic period,
• fetal period.

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Prenatal Development

• Conceptionwhen a sperm penetrates the ovum
• Zygotea fertilized egg
• Germinal periodfirst two weeks after conception
• Embryonic periodweeks three through eight after
  conception
• Fetal periodtwo months after conception until
  birth

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From Conception to Zygote
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Zygote

• A newly fertilized egg
• The first two weeks are a period of rapid cell
  division.
• Attaches to the mothers uterine wall
• At the end of 14 days becomes a cluster of cells
  called an embryo.

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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.

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Embryo

• The embryo is protectively housed in the
  fluid-filled amniotic sac the embryos 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

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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 mothers
  uterine wall.
• The placenta prevents the mothers 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
  mothers blood from reaching the embryo

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Prenatal Development
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Fetal Period

• The period between the beginning of the ninth
  week until birth
• By the end of the third month, the fetus can move
  its arms, legs, mouth, and head
• During the fourth month, the mother experiences
  quickeningshe can feel the fetus moving.
• By the fifth month, the fetus has distinct
  sleepwake cycles and periods of activity.
• During the sixth month, the fetuss brain
  activity becomes similar to that of a newborn
  baby.
• During the final two months, the fetus will
  double in weight.

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Prenatal Development 45 Days
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Prenatal Development 2 months
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Prenatal Influences on Development

• Nutrition
• Anxiety
• Mothers general health
• Maternal age
• Teratogensany agent that causes a birth defect
  (e.g., drugs, radiation, viruses)

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Teratogens

• Substances that pass through the placentas
  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

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Prenatal Development

• Play Teratogens and Their Effects on the
  Developing Brain and Mind (1244) Segment 12
  from The Mind Psychology Teaching Modules (2nd
  edition)

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Smoking and Birth Weight
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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

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Prenatal Brain Development

• Play The Effects of Hormones and the Environment
  on Brain Development (650) Module 2 from The
  Brain Teaching Modules (2nd edition)