What are the Differences Between Dominant and Recessive Genes?
The terms dominant and recessive describe the genetic probability of inheriting a particular gene. Every gene has two copies, which are named alleles. One comes from the side of the mother, the other from the side of the side of the father. Normally, when one of the genes is dominant and the other recessive, the first will be pronounced [1].
The expression of the alleles brings physically visible traits, like eye or hair color. However, an allele can also encode pathological mutations.
The main difference between dominant and recessive genes is when they are expressed. A dominant gene will always express its dominant trait. The recessive traits need two recessive alleles.
Based on the expression difference, it is possible to determine whether an allele (a gene copy) is dominant or recessive [2].
To see an example of how the dominant and recessive genes work, let's consider cystic fibrosis.
Cystic fibrosis is a monogenic, autosomal recessive disease. The expression of this disease depends on one gene, which is found on chromosome 7.
Because cystic fibrosis is a recessive disease, both alleles have to be affected by the mutation. When one of the copies is a healthy dominant gene, the disease will not occur. All the elements encoded by this gene will be expressed in the dominant copy. The defective recessive copy will not be used for protein production [3].
It's important to remember that most of the mutations are passed down recessively. Often, when a mutation happens, it leads to a loss of genetic function. The loss is then compensated by the healthy allele [4, 5]. This is the mechanism that makes the mutated genes recessive.
How Can Your Child Inherit a Dominant or Recessive Disease?
Genetic disorders can be inherited in two main ways: through dominant or recessive genes. The pattern of inheritance follows simple rules. There are three possible configurations of alleles [6].
First, a dominant homozygous configuration. In this case, a person will have two dominant alleles.
Next is a dominant heterozygous. This person will have one dominant and one recessive allele.
The third case is recessive homozygosity. Here, both the alleles are recessive, and only a recessive disease can be transmitted.
Whether your child will inherit the disease or not depends on the genes of you and your partner. To be sure, both of you have to undergo genetic tests.
Especially when one of you suffers from a recessive disease, it is worth checking the genes of the other. In this way, the probability of your child inheriting the disease can be estimated, using a Punnett Square.
Dominant Genes Diseases
Dominant gene diseases are conditions that occur when a mutation in a single copy of a gene is enough to cause a disease. Here are some examples of autosomal diseases:
- Huntington's disease [7]
- Marfan syndrome [7]
- Familial hypercholesterolemia [7]
- Dominant Dystrophic Epidermolysis Bullosa [8]
- Myotonic dystrophy types 1 and 2 [9]
- Polycystic kidney disease [10].
Some of the mutations in alleles can also be found on the X chromosomes. For instance, X-linked diseases include:
- Microphthalmia with Linear Skin Defects (MLS) Syndrome [11]
- Aicardi Syndrome [11]
- Goltz Syndrome (focal dermal hypoplasia) [11]
- Incontinentia Pigmenti (Bloch-Sulzberger Syndrome)[12]
- Oral-Facial-Digital Syndrome I [12]
- X-linked Hypophosphatemic Rickets [13]
- Fragile X Syndrome [14]
- Rett Syndrome [15].
Recessive Genes Diseases
Recessive gene diseases are conditions that occur when an individual inherits two copies of an abnormal gene, one from each parent. Examples of autosomal recessive diseases include:
- Cystic fibrosis [16]
- Sickle cell anemia [10]
- Tay-Sachs disease [10]
- Homocystinuria [10]
- Gaucher's disease [10].
Examples of X-linked chromosome recessive diseases are: