Chapter 11 Complex Inheritance and Human Heredity

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Chapter 11 Complex Inheritance and Human Heredity

• 11.1 Basic Patterns of Human Inheritance

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Recessive Genetic Disorders

• Mendels work went unnoticed by the scientific
  community for about 30 years then it was
  rediscovered in the early 1900s.
• At that time many scientists were interested in
  the cause of diseases and noticed that some
  diseases ran in families.
• Alkaptonuria was the first identified (recessive)
  genetic disorder. Alkaptonuria, from an enzyme
  deficiency, causes black acidic urine and later
  in life affects bones and joints.

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Recessive Genetic Disorders

• A recessive trait is expressed when the
  individual is homozygous recessive for the trait.
  
• Both parents would need to have at least one
  recessive allele.
• Usually the parents are heterozygous (carriers)
  for the disorder.

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Cystic Fibrosis

• Affects the mucus-producing glands, digestive
  enzymes, and sweat glands
• Chloride ions are not absorbed into the cells of
  a person with cystic fibrosis but are excreted in
  the sweat.
• Without sufficient chloride ions in the cells, a
  thick mucus is secreted

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Cystic Fibrosis
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Cystic Fibrosis
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Albinism

• Caused by altered genes, resulting in the absence
  of the skin pigment melanin in hair and eyes
• White hair.
• Very pale skin
• Pink pupils

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Albinism
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Tay-Sachs Disease

• Caused by the absence of the enzymes responsible
  for breaking down fatty acids called gangliosides
  
• Gangliosides accumulate in the brain, inflating
  brain nerve cells and causing mental
  deterioration.
• Death by age 2

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Dominant Genetic Disorders
99.9 of population is homozygous recessive for
achondroplasia
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Huntingtons Disease

• Affects the nervous system
• Latent disorder affects age 30 to 50
• Gradual loss of brain function (holes in brain)
• Genetic test available
• Result of allele mutation at tip of chromosome 4

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Achondroplasia

• Most common form of dwarfism
• 75 of individuals born to parents of average
  size, result of new mutation
• Lethal spontaneous abortion in homozygous
  dominant genotype

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Pedigree Analysis
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Pedigree Analysis

• Are females
• Are males
• Shaded in circles and squares are affected
  individuals
• Roman Numerals (I IV) are generations
• Lines across represent mating
• Lines down represent offspring

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Pedigree Analysis

• Count the number of affected males and affected
  females. If most males and few or no females
  most likely sex linked trait.
• Look at the affected individuals. If every
  individual with the trait has a parent with the
  trait then this trait is dominant. If
  non-affected parents produce an offspring with
  the trait then it is recessive.
• Determine the phenotype and genotype of every
  individual

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Pedigree Analysis

• Affected males 1
• Affected females 2 (not sex linked)
• No affected individual has parent with the trait,
  means recessive
• All affected individuals would be homozygous
  recessive, aa
• All parents of affected individuals would be
  heterozygous, Aa
• Siblings of affected individuals would be
  heterozygous (Aa) or homozygous dominant (AA)

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Pedigree Analysis