Chapter 2: Genes and Heredity

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Chapter 2 Genes and Heredity

• How Traits and Genetic Abnormalities are Inherited

• By Kati Tumaneng
• (for Drs. Cook Cook)

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Dominant-Recessive Traits

• Dominant-Recessive Relationship is a relationship
  between genes where the dominant allele will
  govern a particular trait, and the recessive
  allele will be repressed. To express a recessive
  trait, the individual needs to inherit two
  recessive alleles one on each chromosome.

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Dominant-Recessive Traits

• Dominant Gene Diseases
• Huntington Disease is the most common example.
• Symptoms do not usually appear until after 30,
  causes progressive damage to brain and nervous
  system and involuntary movements

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Dominant-Recessive Traits
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Dominant-Recessive Traits

• Recessive Gene Diseases
• Less common because two recessive alleles need to
  be inherited before the individual shows the
  condition
• Cystic fibrosis most common among Caucasians
  nearly 1 in 22 carry gene
• Sickle cell disease most common in those of
  African or Hispanic descent
• Tay-Sachs disease fatal in childhood

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Dominant-Recessive Traits
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Dominant-Recessive Traits

• X-Linked (Sex-Linked) Traits
• Differences in males and females caused by
  dominant and recessive alleles on the X and Y
  chromosomes.
• Y chromosome small contains little genetic
  material.
• Since many genes on X chromosome do not have
  counterpart on Y, males (XY) more likely to
  suffer recessive disease traits.
• Hemophilia, Duchenne muscular dystrophy, and
  color blindness more likely in males.

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Dominant-Recessive Traits

• X-Linked (Sex-Linked) Traits (cont.)
• Dominant disease alleles on X chromosomes are
  very rare.
• Females are two times more likely to have these
  types of diseases than males.
• Vitamin D-resistant rickets
• Rett syndrome

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Chromosome Abnormalities

• 1 in every 160 live births
• Account for majority of miscarriages
• Errors occur that cause sperm or egg to have a
  missing or extra chromosome
• Down Syndrome extra 21st chromosome

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Down Syndrome
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Chromosome Abnormalities
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Prenatal Screening and Genetic Testing
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Prenatal Screening and Genetic Testing

• Ultrasonography (ultrasound) Images, produced
  by sound waves, of the fetus inside the mothers
  womb. Help physicians monitor fetal growth and
  detect physical defects.
• Amniocentesis Procedure used to detect
  chromosomal and genetic abnormalities in the
  fetus. A needle is inserted through the mothers
  abdomen and uterus and into the amniotic sac, and
  fetal cells are withdrawn from the amniotic
  fluid.
• Chorionic Villus Sampling (CVS) Procedure used
  to detect chromosomal and genetic abnormalities
  in the fetus. A catheter (tube) is inserted into
  the uterus and cells are taken from the chorionic
  layer of the placenta around the fetus.
  Chromosomes are removed to conduct genetic tests.
• National Society of Genetic Counselors
  www.nsgc.org

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Prenatal Screening and Genetic Testing
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• Dominant Disease Alleles on Slide 4 from Cook,
  J. L., Cook, G. (2005). Child development
  Principles and perspectives (1st ed.) (p. 57).
  Boston Allyn and Bacon.
• Recessive Disease Alleles on Slide 6 from Cook,
  J. L., Cook, G. (2005). Child development
  Principles and perspectives (1st ed.) (p. 58).
  Boston Allyn and Bacon.
• Chart on Slide 10 from Cook, J. L., Cook, G.
  (2005). Child development Principles and
  perspectives (1st ed.) (p. 61). Boston Allyn and
  Bacon.
• Ultrasound on Slide 12 from Cook, J. L., Cook,
  G. (2005). Child development Principles and
  perspectives (1st ed.) (p. 63). Boston Allyn and
  Bacon.
• Image on Slide 14 from Cook, J. L., Cook, G.
  (2005). Child development Principles and
  perspectives (1st ed.) (p. 64). Boston Allyn and
  Bacon.
• All other images retrieved from Microsoft
  PowerPoint Clip Art.