Autosomal Disorder Pedigree Analysis
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Autosomal disorders are genetic conditions that are inherited through the autosomes, which are the non-sex chromosomes (chromosomes 1-22 in humans).
When analyzing pedigrees to determine the inheritance pattern of an autosomal disorder, several key rules and characteristics can help identify whether a disorder is autosomal dominant or autosomal recessive. Below is a guide to understanding and identifying these patterns in pedigree analysis.
Autosomal Dominant Disorder
Understanding with Example:
A parent with an autosomal dominant disorder (e.g., Huntington's disease) has a 50% chance of passing the mutated gene to each child.
Pedigree Indicators:
At least one affected parent.
Does not skip generations (vertical pattern).
Roughly equal numbers of affected males and females.
Characteristics:
Inheritance from Either Parent: The disorder can be inherited from either the mother or the father.
Every Generation: The disorder usually appears in every generation. An affected individual has at least one affected parent.
Both Genders Equally Affected: Males and females are equally likely to be affected.
No Carriers: There are no carriers; if an individual has the allele, they express the disorder.
50% Probability: An affected individual has a 50% chance of passing the disorder to their offspring, regardless of the partner's genotype.
Autosomal Recessive Disorder
Understanding with Example:
Two carriers of an autosomal recessive disorder (e.g., cystic fibrosis) have a 25% chance of having an affected child.
Pedigree Indicators:
May skip generations (horizontal pattern).
Affected individuals often have unaffected parents who are carriers.
Affected individuals may have affected siblings but unaffected parents.
Characteristics:
Both Parents as Carriers: The disorder is often seen when both parents are carriers (heterozygous).
Skipping Generations: The disorder may skip generations, appearing only when two carriers have children.
Both Genders Equally Affected: Males and females are equally likely to be affected.
Carriers Present: Individuals who carry one copy of the mutated gene do not exhibit symptoms.
25% Probability: Two carrier parents have a 25% chance of having an affected child, a 50% chance of having a carrier child, and a 25% chance of having a non-carrier child.
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