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Chapter 12.3. Examples of Autosomal Inheritance Patterns. AP Biology Fall 2010. Autosomal Dominant Inheritance. The dominant allele is nearly always expressed, even in heterozygotes

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chapter 12 3

Chapter 12.3

Examples of Autosomal Inheritance Patterns

AP Biology

Fall 2010

autosomal dominant inheritance
Autosomal Dominant Inheritance
  • The dominant allele is nearly always expressed, even in heterozygotes
  • If one parent is heterozygous and the other homozygous recessive, there is a 50 percent chance that any child will be heterozygous
    • Draw a punnette square to illustrate this
    • Cross a normal mother with an affected father
      • aa x Aa
      • aa = normal
      • Aa = affected
autosomal dominant inheritance3
Autosomal Dominant Inheritance
  • If the gene (and its resulting disorder) reduces the chance of surviving or reproducing, its frequency should decrease
    • May not due to mutations, nonreproductive effects, and post reproduction onset
autosomal dominant inheritance4
Autosomal Dominant Inheritance
  • Achondroplasia (dwarfism): is a benign abnormality that does not affect persons to the point that reproduction is impossible
    • The gene is passed on in heterozygotes
autosomal dominant inheritance5
Autosomal Dominant Inheritance
  • Huntington disease is a series degeneration of the nervous system with an onset past the mid-thirties
    • By which time the gene has (usually) been passed from parent to offspring unknowingly
autosomal recessive inheritance
Autosomal Recessive Inheritance
  • Characteristics of this condition:
    • Either parent can carry the recessive allele on an autosome
    • Heterozygotes are symptom-free carriers
    • Homozygotes are affected
    • Two heterozygous parents have a 50 percent chance of producing heterozygous children and a 25 percent chance of producing a homozygous recessive child
    • When both parents are homozygous, all children will be affected
  • Try crossing a carrier mother (Aa) with a carrier father (Aa)
autosomal dominant inheritance7
Autosomal Dominant Inheritance
  • Galactosemia: the inability to metabolize lactose
    • Is an example of autosomal recessive inheritance in which a single gene mutation prevents manufacture of an enzyme needed in the conversion pathway
what about neurobiological disorders
What About Neurobiological Disorders?
  • Patterns of Mendelian genetics are not followed by human neurobiological disorders
  • In most cases a lone gene does not give rise to disorders such as: depression, schizophrenia, or bipolar
  • Researches predict that having certain mutant autosomal alleles increases the chance of developing schizophrenia
    • Mutant alleles are also linked to bipolar disorder and depression