Here's why:
* Haploinsufficiency: This refers to a situation where having only one copy of a gene is not enough for normal function. In these cases, a mutation or deletion on one chromosome can lead to a disease or disorder.
* Haplosufficiency: This is the opposite of haploinsufficiency. It means that one functional copy of a gene is sufficient to produce enough of the gene product for normal function. This is why even if a gene is only present on one chromosome, it can still be expressed and function properly.
Examples of haplosufficient genes:
* Many genes involved in basic cellular processes: These genes are essential for survival, so having two copies is not always necessary.
* Genes involved in development: Some developmental genes are haplosufficient, allowing for normal development even if one copy is missing.
* Genes with redundant functions: If a gene has a duplicate gene that performs the same function, then losing one copy may not have a significant impact.
It's important to note that:
* Not all genes are haplosufficient. Some genes are haploinsufficient, meaning that two copies are necessary for normal function.
* The level of expression of a haplosufficient gene can be lower than if both copies were present.
* The phenotype of a haplosufficient gene can sometimes be affected by environmental factors or the presence of other genes.
Overall, haplosufficiency allows for a degree of genetic flexibility, enabling organisms to tolerate the loss of one copy of certain genes without severe consequences.
