A child is born witrh cystic fibrosis-a recessive trait. However, both his parents do not exhibit the trait. How is this possible?
In case you are not familiar with bobpursley's terms, here is a more detailed explanation.
With recessive traits, a person must have both genes for the recessive condition (homozygous) to show the physical trait. If one of the gene pair are dominant, it will prevent the recessive gene from being expressed in the physical traits (phenotype). That person will be a carrier for that trait, having the genes in the genotype but not showing the trait in the phenotype. However, there is a 25% chance that both carrier parents will contribute the recessive gene to an offspring, making the offspring homozygous for that trait. This means that the child will show the trait in the phenotype.
This is true for any recessive trait.
I hope this helps a little more. Thanks for asking.
I suspect his parents are both carriers, carrying the recessive gene, but because neither is homozygous, neither have the disease.
In order to understand how a child can be born with cystic fibrosis (a recessive trait) even if both parents do not exhibit the trait, we need to understand the underlying genetics.
Cystic fibrosis is caused by a mutation in a gene called the CFTR gene. This gene is responsible for producing a protein that regulates the flow of salt and water in and out of cells, particularly in the lungs and digestive system. The mutation in the CFTR gene leads to the production of a defective protein, causing the characteristic symptoms of cystic fibrosis.
Cystic fibrosis is an autosomal recessive disorder, which means that a person needs to inherit two copies of the defective gene (one from each parent) in order to manifest the disease. A person who has only one copy of the defective gene is called a carrier and does not show symptoms of the disorder.
In the scenario you described, it is possible for both parents to be carriers of the cystic fibrosis gene without exhibiting any symptoms. Each parent has one normal copy of the CFTR gene and one mutated copy. Since cystic fibrosis is a recessive trait, it is only expressed when both copies of the gene are mutated.
When these carrier parents have a child, there is a 25% chance that the child inherits two copies of the mutated gene (one from each parent) and will therefore develop cystic fibrosis. This outcome can occur randomly during the process of genetic recombination that happens during the formation of sperm and egg cells.
So, even though both parents do not have cystic fibrosis, they can still pass on the mutated gene to their child, resulting in the child being born with the disorder.