D3.2.13 Pedigree charts to deduce patterns of inheritance of genetic disorders Notes

Pedigree Charts Visualize Genetic Inheritance

1. Pedigree charts allow us to map patterns of inheritance, revealing whether traits are dominant, recessive, autosomal, or sex-linked.
2. They are especially useful for investigating genetic disorders in humans, where controlled breeding experiments are not possible.

Symbols and Conventions in Pedigree Charts

Identifying Patterns of Inheritance

Autosomal Recessive Traits

1. Characteristics:
   1. Trait may skip generations.
   2. Unaffected parents can have affected children.
   3. Both males and females are equally affected.
2. Genotypes:
   1. Affected individuals: aaaaaa (homozygous recessive).
   2. Carriers: AaAaAa (heterozygous, unaffected).

Autosomal Dominant Traits

1. Characteristics:
   1. Trait appears in every generation.
   2. Affected individuals have at least one affected parent.
   3. Both males and females are equally affected.
2. Genotypes:
   1. Affected individuals: AAAAAA or AaAaAa.
   2. Unaffected individuals: aaaaaa.

Inbreeding Increases Genetic Disorders

1. Inbreeding increases the likelihood of genetic disorders because:
   1. Shared Genes: Close relatives are more likely to carry the same recessive alleles.
   2. Higher Risk: Offspring are more likely to inherit two copies of a recessive allele.
2. This is why many societies prohibit marriage between close relatives.

Steps to Analyze a Pedigree Chart

1. Identify the Trait:
   1. Is it dominant or recessive?
   2. Is it autosomal or sex-linked?
2. Determine Genotypes:
   1. Start with affected individuals.
   2. Work backward to deduce parental genotypes.
3. Predict Probabilities:
   1. Use the inheritance pattern to predict future outcomes.

The Role of Inductive and Deductive Reasoning

1. Inductive Reasoning: Observing specific cases to form a general conclusion.
   1. Recognizing that unaffected parents can have affected children suggests a recessive trait.
2. Deductive Reasoning: Using general principles to predict specific outcomes.
   1. If a trait is X-linked, affected males must inherit the allele from their mothers.