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Chapter 12.3

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

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  1. Chapter 12.3 Examples of Autosomal Inheritance Patterns AP Biology Fall 2010

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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)

  7. 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

  8. 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

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