Genes and Behavior

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Genes and Behavior

• Monozygotic, or identical, twins develop from a
  single fertilized egg and have identical genes.
• Dyzygotic, or fraternal, twins develop from two
  eggs and share only half of their genes, like any
  other sibling set.
• Studying sets of twins is a useful and
  informative way to know more about the influence
  of genes on behavior.

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Genes and Behavior

• From twin studies and other genetic research,
  its still unclear
• How genes shape mental processes and behavior
• Which aspects of the environment are most
  important in influencing psychological processes
• How genes and environment work together to shape
  mental processes and behavior

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Genetic Principles

• Chromosomes
• Most animal and plant cells contain a nucleus
  with hereditary material instructions in the
  form of strands called chromosomes.
• Humans have 46 chromosomes 23 pairs in every
  body cell except for the sex cells. Sperm and ova
  each contain 23 unpaired chromosomes that unite
  at conception.

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Genetic Principles

• Genes
• The genes that form the sections of the
  chromosomes direct an organisms development
• Genes control protein production in order to
  produce specific characteristics a specific
  group of genes will exert a large influence over
  height, weight, or eye color.

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Figure 5.1

• Figure 5.1 Genes are sections of chromosomes in
  the nuclei of cells (scale is exaggerated for
  illustration purposes).

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Genetic Principles

• Genes
• Genes are composed of DNA, special chemicals that
  control the production of RNA.
• RNA in turn controls the production of proteins.

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Genetic Principles

• Genes
• If one receives one gene for wavy hair and
  another for straight hair, the hair will be wavy.
• Gene for wavy hair is a dominant gene.

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Genetic Principles

• Genes
• A recessive gene will only show its effects if 2
  identical genes are present (homozygous
  condition). You must receive a gene for blue eyes
  from both parents in order to develop blue eyes.
  
• The gene for blue eye color is a recessive gene.

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Genetic Principles

• Sex-linked genes
• The sex chromosomes determine whether an
  individual will become a male or female.
• There are two types of sex chromosomes, called X
  and Y.
• Females receive an X from each parent males
  receive an X from mother and a Y from father.

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Genetic Principles

• Sex-linked genes
• Genes that are on the X-chromosome are called
  sex-linked genes.
• The influence of these genes is seen more often
  in men than in women.

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Genetic Principles

• Sex-linked genes
• A man may have the hemophilia gene on his
  X-chromosome. There is no gene on the Y, and so
  the trait manifests.

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Genetic Principles

• Genetic screening
• Genetic diseases have been of great concern.
  Technology now allows us to identify and localize
  genes that cause such diseases.
• Some examples of these are
• Alzheimers Disease
• Huntingtons Disease
• PKU
• Some interesting issues have arisen

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Genetic Principles

• Heritability
• But even traits traced to a single gene may be
  strongly environmentally influenced.
• PKU causes profound mental retardation, but only
  if the affected persons diet includes foods
  containing a certain enzyme.

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Genetic Principles

• Heritability
• Heritability is measured from 0 to 1
• 0 means that almost none of the variance in the
  trait in due to heredity
• 1 signifies that variance in the trait is due
  entirely to heredity

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Temperament and Gene-Environment Interaction

• Research suggests that temperament is stable over
  much of the lifespan
• Kagan and his associates were able to strongly
  relate infant temperament to later levels of
  sociability.
• Genetic influences make contributions to
  temperament, although environment is also a
  factor.

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The Fetus and the Newborn

• Prenatal Development
• The growth and changes that occur before birth
  are referred to as prenatal development. There
  are identifiable stages of this period of life.

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The Fetus and the Newborn

• Prenatal development
• Zygote Fertilized egg cell
• Blastula
• Gastrula
• Embryo 2 to 8 weeks after conception
• Fetus 8 weeks after conception until birth

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The Fetus and the Newborn

• Prenatal development
• Prenatal brain development
• By seven weeks the hindbrain and midbrain are
  developed enough to produce movements.
• By 36 weeks those brain structures produce head
  and eye movements in response to sounds, a
  sleep-wake cycle, and REM sleep.
• The cerebral cortex is relatively inactive during
  this period.

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The Fetus and the Newborn

• Prenatal development
• The maternal-fetal connection
• Everything that mother consumes reaches the baby
  through the placenta.
• If mothers nutrition and prenatal care are poor
  or deficient, baby will also be deprived.
• If mother drinks, uses drugs, or smokes, baby
  will receive these substances, often with serious
  consequences.

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The Fetus and the Newborn

• Prenatal development
• Low-birth weight and premature infants
• Small and premature babies have a higher risk of
  dying in infancy.
• They are more likely to have impaired brain
  development.
• If they survive they are at higher risk of
  behavioral and academic problems.
• Low birth weight and prematurity correlate with
  the factors that cause these problems, even if
  they are not in fact the direct cause.

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The Fetus and the Newborn

• Prenatal development
• Fetal alcohol syndrome
• If mother drinks alcohol during pregnancy, the
  baby is likely to be born with fetal alcohol
  syndrome (FAS)
• FAS is characterized by stunted growth of the
  head and body, facial, cranial and ear
  malformations, neurological damage, learning
  disabilities, and mental retardation.

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The Fetus and the Newborn

• Prenatal development
• There is a milder version, fetal alcohol effects
  (FAE).
• A child with FAE appears normal but has impaired
  academic skills and mild behavioral problems.
• The more alcohol mother drinks, and the longer
  she continues drinking, the greater the risk to
  the developing baby.
• There is no safe level of alcohol consumption
  during pregnancy.

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The Fetus and the Newborn

• Prenatal development
• During prenatal development, growing neurons need
  persistent excitation to survive.
• Alcohol facilitates GABA, the main inhibitory
  neurotransmitter of the brain which leads the
  neurons to self-destruct.
• Any chemicals that increase activity at
  inhibitory synapses, such as tranquilizers,
  anesthetics, and anti-depressants, should be
  avoided.

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The Fetus and the Newborn

• Prenatal development
• Maternal smoking
• Smoking (before and after birth) has been
  associated with an increased risk of SIDS.
• Conduct disorder has been found to correlate with
  mothers smoking during pregnancy more strongly
  than with fathers antisocial behavior, SES, lack
  of supervision, or use of harsh punishment by the
  parents.

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Behavioral Capacities of the Newborn

• Newborns learning and memory
• Older infants (2-3 months old) show ability to
  learn responses and remember them for days
  afterwards, such as kicking their legs to make a
  mobile move.
• Nine-month-olds can learn to press a lever to
  move a toy train around a track, and can retain
  this memory for a fairly long time.