User:Sbakerrrrr01/sandbox

Types of Mutations
Hearing loss is frequently attributed to genetic factors. There are 3 different types of mutations that can cause deafness.

Dominant mutation
For inheritance to occur with a dominant mutation, there only needs to be 1 altered gene for the mutation to be displayed.

Recessive mutation
Recessive mutations only occur when both of the genes are altered. It takes more than 1 gene for the trait to be displayed because its not strong enough on its own. If one recessive gene is passed on that is paired with an unaltered gene, it produces a person which is referred to as a genetic carrier. A carrier is someone who doesn’t show the mutation but contains the genetic information for the mutation.

Spontaneous mutation
This is a mutation that randomly produced for the first time in an individual and it is not something that is inherited from a previous generation.

Types of Inheritance
There are 4 different types of inheritance with respect to mutations.

Inheritance of a Dominant Mutation
The inheritance of a dominant mutation occurs when a child receives one copy of an altered gene and that mutation is always expressed. If only one parent has the dominant gene, there is a 50% chance for each child to express that mutation.

Inheritance of a Recessive Mutation
Inheritance of an X-linked mutation is a mutation that is carried on the sex chromosomes. This is different from the previous 2 because it differs between females and males. Females have 2 X chromosomes, so when the mutation is passed to them, they don’t have any other option than receiving one X chromosome from their mother, so if that is altered, then its guaranteed they will have the altered chromosome. Even though they will have the altered gene, it doesn’t mean they will show it because they will also have the chance to get an unaltered gene from their father, which would block the effects of the altered gene. In males, they have 1 X and 1 Y chromosome, so if they receive an altered gene, they will show the mutation because they have no other gene to block the effects of the altered gene.

Inheritance of an X-linked Mutation
In the inheritance of a recessive mutation, the child has to receive 2 altered genes in order for that child to express the mutation. If they get only one of the altered copies, they will not express the mutation because the more dominant gene will overshadow it, producing a carrier. If both parents are carriers, they have the chance of giving a child the inheritance of a recessive mutation because the child could have 2 copies of the altered gene. If both parents are carriers, there is a 1 in 4 chance that their child will express the mutation.

Inheritance of a Mitochondrial Mutation
The final type of inheritance is the inheritance of a mitochondrial mutation. Mitochondria are small organelles found within cells that provide energy for the cell to continue its natural processes. Mitochondria are unique in the fact that they have their own DNA, which means they also have their own genes. These genes are passed down from generation to generation and if there happens to be a mutation, it will also be passed down. In reproduction, only the egg (and not the sperm) passes the mitochondrial DNA onto the child. This means only the mother can pass down an altered gene. If the mother has an alteration, all of the children will have the altered gene, whereas the male’s mitochondrial DNA doesn’t matter at all.

With respect to hearing loss, around 75-80% of all cases are inherited by recessive genes, 20-25% are inherited by dominant genes, 1-2% are inherited by X-linked patterns, and fewer than 1% are inherited by mitochondrial inheritance.

Forms of Deafness
When looking at the genetics of deafness, there are 2 different forms, syndromic and nonsyndromic. Both of these can be caused by inheritance and genetics. Syndromic deafness occurs when there are other medical problems aside from deafness in an individual. This accounts for around 30% of deaf individuals who are deaf from a genetic standpoint. Nonsyndromic deafness occurs when there are no other problems associated with an individual other than deafness. From a genetic standpoint, this accounts for the other 70% of cases, which attributes to the vast majority of hereditary hearing loss. Syndromic cases occur with diseases such as Usher syndrome, Stickler, Waardenburg syndrome, Alport, and Neurofibromatosis type 2. These are diseases that have deafness as one of the symptoms or a common feature associated with it. The genetics that correspond with these various diseases are very complicated and are difficult to explain scientifically because the cause is unknown. In nonsyndromic cases where deafness is the only ‘symptom’ seen in the individual it is easier to pinpoint the physical genes.