Every person is unique. Part of what makes each person unique is his or her genes.
Genes are the instructions inside each cell. They control how someone will look and how his or her body works. Genes carry instructions that tell cells how to work and grow. Cells are the building blocks of the body. Every part of your body is made up of billions of cells working together. Since everyone has slightly different genes, everyone has a different set of instructions.
Children inherit pairs of genes from their parents. A child gets one set of genes from the father and one set from the mother. These genes can match up in many ways to make different combinations. This is why many family members look a lot alike and others don’t look like each other at all. Genes can also increase the risk in a family for getting certain health conditions.
Some diseases are caused when there is a change in the instructions in a gene. This is called a ‘mutation’. Every person has mutations in some genes – sometimes these changes have no effect or are even slightly helpful. But sometimes they can cause disease. Thousands of diseases are caused by a specific change in a single gene, or a certain few genes. Many of these diseases are rare. Mutated genes can be inherited (passed down from parent to child). However, sometimes they are the result of a new genetic change within an individual, so it may not be present in other family members. The following are different types of inheritance patterns that can be seen.
If a condition is an autosomal recessive genetic disorder, it means that:
- It affects males and females equally.
- Two non-working copies of the gene are needed in order for a person to be affected by the condition.
With autosomal recessive conditions, the parents usually do not have any symptoms of the condition themselves, but they carry one non-working copy of the gene. They are called "carriers.” Even though they are not affected, they can still pass on the non-working gene to their children.
If two parents are carriers of the same genetic condition, then there is a chance that their children will be affected with that condition.
- There is a 1 in 4 chance (25%) of having a child affected with that genetic condition.
- There is a 1 in 4 chance (25%) of having a child who is neither affected with nor a carrier of that condition.
- There is a 1 in 2 chance (50%) of having a child who is a carrier of the condition. (They have one working copy and one non-working copy of the gene and most likely will be unaffected)
These possible outcomes and their chances are the same for each pregnancy where both parents are carriers.
If a condition is an autosomal dominant genetic disorder, it means that:
- It affects males and females equally.
- Only one non-working copy of the gene is needed in order for a person to be affected by the condition.
With autosomal dominant conditions, one parents usually also has the condition. In some cases, the child may have a new mutation (or de novo mutation) and be the first in the family to be affected with this condition.
If one parent is affected with a genetic condition, then there is a chance that his or her children will be affected with that condition.
- There is a 1 in 2 chance (50%) of having a child affected with that genetic condition.
- There is a 1 in 2 chance (50%) of having a child who is neither affected with nor a carrier of that condition.
These possible outcomes and their chances are the same for each pregnancy where one parent is affected.
If a condition is an x-linked recessive genetic disorder, it means that:
- It affects males more frequently than females.
- At least one working copy of the gene is needed in order for a person to not be affected by the condition.
X-linked conditions are different from autosomal conditions because they are inherited by the sex chromosomes, which are different in males and females. Males have one X chromosome and one Y chromosome and females have two X chromosomes. These conditions can be inherited from either the mother or the father.
If it is inherited from the mother, she usually will not have the condition herself, but carries one non-working copy of the X chromosome and one working copy. Her one working copy is enough to keep her healthy. She is called a "carrier.” Carriers often do not have symptoms of the genetic condition, but they can still pass on the non-working gene to their children. In some rare instances, the mother may show signs of the condition because of a process called lyonization. Because females have two copies of the X chromosome and males have only one, one copy of the female X chromosome is turned off at random. Unequal lyonization occurs when the working copy of the X chromosome is turned off more frequently than the non-working copy.
If it is inherited from the father, he will usually be affected with the condition.
If the mother carriers the x-linked recessive genetic condition, then there is a chance that her children will be affected with that condition.
- There is a 1 in 4 chance (25%) of having a male child affected with that genetic condition.
- There is a 1 in 4 chance (25%) of having a male child who is neither affected with nor a carrier of that condition.
- There is a 1 in 4 chance (25%) of having a female child who is a carrier, but not affected that condition.
- There is a 1 in 4 chance (25%) of having a female child who is neither affected with nor a carrier of that condition.
If the father is affected with the x-linked recessive genetic condition, then there is a chance that his children will be affected with that condition.
- There is a 1 in 2 chance (50%) of having a female child who carries that genetic condition.
- There is a 1 in 2 chance (50%) of having a male child who is neither affected with nor a carrier of that condition.
In other words, all female children will be carriers and all male children will not be carriers nor affected.
If a condition is an x-linked dominant genetic disorder, it means that:
- It affects females more frequently than males.
- Only one non-working copy of the gene is needed in order for a person to be affected by the condition.
X-linked conditions are different from autosomal conditions because they are inherited by the sex chromosomes, which are different in males and females. Males have one X chromosome and one Y chromosome and females have two X chromosomes. These conditions can be inherited from either the mother or the father.
If the mother carriers the x-linked dominant genetic condition, then there is a chance that her children will be affected with that condition.
- There is a 1 in 2 chance (50%) of having a child affected with that genetic condition.
- There is a 1 in 2 chance (50%) of having a child who is neither affected with nor a carrier of that condition.
If the father is affected with the x-linked dominat genetic condition, then there is a chance that his children will be affected with that condition.
- There is a 1 in 2 chance (50%) of having a female child who is affected with that genetic condition.
- There is a 1 in 2 chance (50%) of having a male child who is not affected with that condition.
In other words, all female children will be affected with the genetic condition and all male children will not be affected.
Autosomal Recessive Inheritance
