Inheritance Patterns

Example of a Recessive Trait in Humans

Observation: The given pedigree chart shows that neither of the parents expresses the trait, but both male and female children exhibit it. This pattern suggests the inheritance of a **recessive trait**.

Example of such a trait in humans:

An example of a recessive trait that follows this pattern is **cystic fibrosis**.

• Cystic fibrosis is caused by a mutation in the CFTR gene, which leads to the production of thick mucus in the lungs and digestive system.
• The condition is inherited in a recessive manner, meaning both parents must be carriers (heterozygous) for the child to inherit the disease.
• Even though neither parent shows symptoms, they can pass on the mutated gene to their offspring, who can then express the trait if they inherit the mutated gene from both parents.

Analyzing the Pedigree Chart and Inheritance Pattern

Step 1: Analyzing the Pedigree Chart

- In the pedigree chart, neither of the parents shows the trait (as both the father and mother are represented without filled circles or squares).
- However, both the male and female children (represented by filled circles and squares) show the trait.
- This suggests that the trait is recessive in nature. Both parents are carriers of the trait (heterozygous) and pass it on to the offspring.

Step 2: Explanation of the Inheritance Pattern

- The trait is inherited in a recessive manner, and both parents must be carriers of the recessive allele (genotype Aa) for the trait to be expressed in their children.
- Since the trait is expressed in both male and female children, this suggests autosomal inheritance.

Step 3: Conclusion

- The parents are carriers of a recessive allele (genotype Aa), and the trait is autosomal recessive. The children inherited the recessive allele from both parents (genotype aa), resulting in the expression of the trait.

• • Individual 1 (B): Possible genotype =
  • Individual 2 (A): Possible genotype =
    (Since their child (individual 8) has blood group O, both parents must carry the allele.)
• • Individual 5 (AB): Antigens present = A and B antigens
  • Individual 8 (O): Antigens present = None (no A or B antigen present on RBC membrane)