chapter 12.3 examples of autosomal inheritance patterns ap biology fall 2010
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Chapter 12.3
Examples of Autosomal Inheritance Patterns
AP BiologyFall 2010
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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
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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
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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
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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
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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)
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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
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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