Heredity Influences on Development Chapter 3

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Heredity Influences on DevelopmentChapter 3

• Dr. Pelaez

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Principles of Heredity Transmission

• The Genetic Code
• Conception is the moment of fertilization, when a
  sperm penetrates an ovum, forming a zygote.
• The zygote contains 46 chromosomes, consisting of
  thousands of chemical segments, or genes.
• Genes are hereditary blueprints for development
  that are passed on unchanged from generation to
  generation.
• Chromosomes come in matching pairs. (23
  chromosomes from each parent.)

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• Growth of the Zygote and Production of Body Cells
• The zygote moves through the fallopian tube
  toward the uterus, and begins the process of
  mitosis.
• The zygote first divide into 2 cells, then 2
  become 4, 4 become 8, 8 become 16, etc.
• Before each division, the zygote duplicates its
  46 chromosomes.

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• Germ (or Sex) Cells
• The germ cells are the sex cells of the zygote.
• The germ cells function is to produce gametes,
  which are either sperm in males or ova in
  females.
• Meiosis occurs when the male germ cell in the
  testes produces sperm and when the female germ
  cell in the ovaries produces ova.
• Often cross-over takes place. This is when
  there is an exchange of genetic material.

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• Multiple Births
• Multiple births occur when the are two people who
  share a genotype. When the zygote begins the
  process of mitosis it may begin to split into
  identical cells. At this moment two individuals
  have been formed. This is an example of
  monozygotic twins.
• Dizygotic twins are more common. These are twins
  that result when a mother releases two ova at the
  same moment and each is fertilized by a different
  sperm.

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• The 23rd pair of chromosomes
• The sex of the zygote is determined by the 23rd
  pair of chromosomes.
• For a female sex, both of these sex chromosomes
  are an X chromosome.
• For a male sex, the 23rd pair consists of one X
  chromosome and one Y chromosome.
• The purpose of our genes..
• Our genes are responsible for the construction of
  our enzymes and other proteins.
• These genes are essential in order to form new
  cells and their specific functions.
• Other genes are accountable for regulating the
  pace of development.

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• How are genes expressed?
• Simple Dominant-Recessive Inheritance
• Alleles human characteristics that are
  influenced by one pair of genes (one from the
  mother, one from the father).
• 1) Dominant-recessive a pattern of inheritance
  in which one allele dominates another so that its
  phenotype is only expressed
• 2) Dominant a powerful gene expressed
  phenotypically masking the effect of a less
  powerful gene (i.e., a gene for normal vision)
• 3) Recessive a less powerful gene not expressed
  phenotypically when paired with a dominant allele
  (i.e., a gene for nearsightedness)

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• Codominance
• Codominance The phenotype produced is a
  compromise between the two genes.
• Sex linked Inheritance
• Genes that are determined by genes located on the
  sex chromosomes (i.e., red/green color blindness)

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• Genetic Imprinting
• A process in which particular gene pairs are
  biochemically marked so that only one parents
  allele is expressed, regardless of its
  composition.
• Polygenic Inheritance
• Human characteristics that are influenced by many
  pairs of alleles (i.e., height, weight,
  intelligence, skin color, temperamental
  attributes, susceptibility to cancer).

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Chromosomal and Genetic Abnormalities

• Congenital defects are those that are present at
  birth, although many are not detectable when the
  child is born.
• Chromosomal Abnormalities
• Abnormalities of Sex Chromosomes
• Involve the 23rd pair sex chromosomes.
• Males may be born with an extra X or Y
  chromosome.
• About 1 in every 1,000 individual has an X
  chromosome that is fragile and may have separated
  into two or more pieces, known as the Fragile-X
  syndrome.

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• Autosomal Abnormalities
• 22 pairs of chromosomes that are similar in males
  and females
• The most common occurs when an abnormal
  sperm/ovum carrying an extra autosome combines
  with a normal gamete to form a zygote that has 47
  chromosomes (i.e., Down syndrome, or trisomy-21).
• Causes of Chromosomal Abnormalities
• Most chromosomal abnormalities result from the
  uneven segregation of chromosomes during the
  meiosis of male and female germ cells.
• Aging-ova hypothesis is another cause of
  chromosomal abnormalities found in the offspring
  of older mothers.

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• Genetic Abnormalities
• Mutations changes in chemical structure of one
  or more genes that produce a new phenotype.
• Genetic abnormalities may occur from mutations.
• Mutations may be induced by
• toxic industrial waste
• radiation
• agricultural chemicals that enter the food supply
• additives and preservatives in processed foods

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Applications Genetic Counseling, Prenatal
Detection, and Treatment of Hereditary Disorders

• Genetic Counseling
• Genetic counseling is a service that helps
  prospective parents to assess the likelihood that
  their children will be free of hereditary
  defects.
• Counselors usually begin by obtaining a complete
  report of family history.

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• Prenatal Detection
• The overall rate of chromosomal abnormalities
  dramatically increases after the age of 35. A
  prenatal screening known as amniocentesis is a
  method performed by extracting amniotic fluid
  from a pregnant woman that can be tested for
  chromosomal abnormalities and other genetic
  defects.

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• Disadvantage
• Amniocentesis is not easily performed before the
  11th 14th week of pregnancy.
• Alternative procedures
• Chorionic villus sampling (CVS) collects tissue
  and can be performed during the 8th or 9th week
  of pregnancy
• Ultrasound scanning the womb with sound waves
  most useful after the 14th week of pregnancy

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• Treating Hereditary Disorders
• New medical and surgical techniques, performed on
  fetuses have made it possible to treat some
  hereditary disorders
• Delivering drugs or hormones to the unborn
  organism by performing bone marrow transplants
• Surgically repairing womb genetically transmitted
  defects of the heart, neural tube, urinary tract,
  and respiratory system.
• Germline gene therapy

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Hereditary Influences on Behavior

• Behavioral Genetics is the scientific study of
  how genotype interacts with the environment in
  order to determine behavioral attributes such as
  intelligence, personality, and mental health.
• Methods of Studying Heredity Influences
• Heritability is the amount of variability in a
  trait that is attributable to hereditary factors.
• Selective breeding experiment
• Family studies
• Estimating the Contribution of Gene and
  Environment
• Gene Influences
• Nonshared Environmental Influences (NSE)
• Shared Environmental Influences (SE)

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• Heredity Influences in Intellectual Performance
• Plomin et al (1997)
• Wilson (1978)
• Heredity Contributions to Personality
• Twin data may be used to estimate genetic
  contributions
• There is a heavy influence by the environment
• (i.e., Nonshared Environmental influences (Rowe,
  1994))
• For example, parents who often treat sons
  differently than daughters, or first-born
  children differently than later-borns.

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• Heredity Contributions to Behavior Disorders and
  Mental Illness
• There is strong indication that schizophrenia is
  genetically influenced.
• Schizophrenia is a serious mental illness
  characterized by severe disturbances in logical
  thinking, emotional expression, and social
  behavior.
• Heredity may also contribute to abnormal
  behaviors such as alcoholism, criminality,
  depression, hyperactivity, manic-depressive
  psychosis, and a number of neurotic disorders.

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Heredity and Environment as Developmental
Co-conspirators

• The Canalization Principle
• There are multiple pathways along which an
  individual might develop.
• Nature and nurture combine to determine these
  pathways.
• Either genes or the environment may limit the
  influence on development by other factors.

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• The Range-of-Reaction Principle
• Range of reaction is when an individual genotype
  establishes a range of possible responses to
  different kinds of life experiences.
• Gottesman (1963)
• Genotype/Environment Correlations
• Passive Genotype/Environment Correlations
• Evocative Genotype/Environment Correlations
• Active Genotype/Environment Correlations