is cystic fibrosis dominant or recessive

2 min read 10-03-2025

is cystic fibrosis dominant or recessive

Cystic fibrosis (CF) is a genetic disorder that primarily affects the lungs and digestive system. Understanding how it's inherited is crucial for family planning and genetic counseling. So, is cystic fibrosis dominant or recessive? The answer is: recessive.

Understanding Recessive Inheritance

To understand why CF is recessive, we need to look at genes and alleles. Each person inherits two copies of every gene, one from each parent. These copies are called alleles. In the case of CF, the gene responsible is called the CFTR gene.

There are two main types of CFTR alleles:

Normal Allele: This allele produces a functional CFTR protein, which is vital for proper lung and digestive function.
Mutated Allele: This allele produces a faulty or non-functional CFTR protein, leading to the symptoms of cystic fibrosis.

Because CF is recessive, an individual needs to inherit two copies of the mutated CFTR allele (one from each parent) to develop the disease. Having just one mutated allele makes a person a carrier. Carriers don't typically show symptoms but can pass the mutated allele to their children.

What Happens if You Inherit One Mutated Allele?

If you inherit only one mutated CFTR allele, you're a carrier. You won't experience the symptoms of cystic fibrosis because the one normal allele produces enough functional CFTR protein to compensate. However, you can still pass the mutated allele to your children.

What Happens if You Inherit Two Mutated Alleles?

If you inherit two mutated CFTR alleles, one from each parent, you will have cystic fibrosis. This is because there is no functional CFTR protein to regulate the movement of salt and water in and out of cells. This leads to the buildup of thick mucus in the lungs and other organs, causing various health issues.

How Cystic Fibrosis is Inherited: A Punnett Square Example

Let's illustrate this with a Punnett Square, a tool used to predict the probability of inheriting certain genotypes and phenotypes:

Let's say 'C' represents the normal allele and 'c' represents the mutated allele.

	C	c
C	CC	Cc
c	Cc	cc

CC: Individual has two normal alleles; they do not have CF and are not a carrier.
Cc: Individual has one normal and one mutated allele; they are a carrier but do not have CF.
cc: Individual has two mutated alleles; they have cystic fibrosis.

This Punnett Square shows that if both parents are carriers (Cc), there's a 25% chance their child will inherit two mutated alleles (cc) and have CF, a 50% chance their child will be a carrier (Cc), and a 25% chance their child will not have CF and not be a carrier (CC).

Genetic Testing and Family Planning

Genetic testing can determine whether someone carries the mutated CFTR allele. This information is incredibly valuable for couples planning to have children, allowing them to make informed decisions based on their risk of having a child with cystic fibrosis.

Conclusion

Cystic fibrosis is a recessive genetic disorder, meaning an individual needs two copies of the mutated CFTR gene to develop the condition. Understanding this mode of inheritance is vital for genetic counseling, family planning, and managing the condition effectively. If you have concerns about cystic fibrosis in your family, consult a genetic counselor for personalized guidance.