DNA Score and DNA Matching

Rewritten on: February 28, 2025

This article explains the mechanisms of dominant and recessive inheritance, and introduces the significance of the DNA Score and DNA Matching services, which allow you to comprehensively assess the risk of hereditary diseases.

What Are "Dominant Inheritance" and "Recessive Inheritance"? ― Understanding the Basics of Heredity

One of the fundamental concepts in heredity is the existence of two patterns: "dominant inheritance" and "recessive inheritance." This concept originates from "Mendel's Laws," discovered by Gregor Mendel in the 19th century through his pea plant crossbreeding experiments, and remains one of the most important foundational theories in modern genetics [ref:1].

In 2017, the Genetics Society of Japan recommended new terminology because the traditional terms tended to cause misunderstanding — proposing terms roughly equivalent to "manifest" and "latent" traits [ref:2]. "Dominant" does not mean "superior"; it simply means a trait that tends to appear on the surface, while "recessive" does not mean "inferior" but rather a trait that tends to remain hidden. This article explains both concepts while primarily using the more widely known conventional terms.

The Mechanism of Dominant Inheritance

When a disease follows a dominant inheritance pattern, having even a single copy of the gene mutation associated with that disease is enough to cause the disease to develop. Humans carry two copies (alleles) of each gene, one inherited from the father and one from the mother, but in dominant inheritance, a mutation in just one of the two is enough for the trait to manifest.

If either the father or the mother has the disease, the statistical probability that a child will develop the same disease is 1/2 (50%). Well-known examples of dominant inheritance disorders include Huntington's disease, Marfan syndrome, and familial hypercholesterolemia [ref:3]. Because these conditions carry a risk of onset from inheriting a mutated gene from just one parent, understanding family history is extremely important in genetic counseling.

The Mechanism of Recessive Inheritance and Carriers

Recessive inheritance is a bit more complex. Having just one copy of the gene mutation responsible for the disease is not enough to cause it to develop. The disease only appears when both alleles carry the mutation — that is, when the person is "homozygous" for the mutation.

A person who has just one copy of the mutation and does not develop the disease is called a "carrier" of that disease gene. Because carriers appear completely healthy, it is not uncommon for someone to go through life without ever realizing they are a carrier.

The issue arises when both partners in a couple happen to be carriers of the same gene. In this case, the likelihood that a child will develop the disease increases, with a probability of 1/4 (25%). In other words, a child born to two carrier parents has a 1-in-4 chance of developing the disease. In addition, 1 in 2 children (50%) will become carriers like their parents, and the remaining 1 in 4 (25%) will not carry the mutated gene at all.

• Dominant inheritance: Onset occurs with just one gene mutation (50% risk of onset)
• Recessive inheritance: Onset occurs only when both gene mutations are present (25% risk of onset if both parents are carriers)
• Carrier: A person who has just one copy of a disease gene mutation but does not develop the disease
• Consanguineous marriage increases the likelihood of sharing the same gene mutation, raising the risk of recessive genetic diseases

Consanguineous Marriage and the Risk of Recessive Inheritance

Marriages between relatives, such as between cousins, who are more likely to carry the same gene mutations, tend to have a higher likelihood of recessive genetic diseases developing. This is because the probability of inheriting the same gene mutation from a common ancestor is far higher than for unrelated individuals.

Well-known recessive genetic disorders include cystic fibrosis (CF), phenylketonuria (PKU), and sickle cell disease. For example, in Western countries, about 1 in 25 people is estimated to be a carrier of cystic fibrosis, and about 25% of children born to two carrier parents develop the disease [ref:3].

There are thousands of diseases related to heredity, and examining the risk of each one individually would take an enormous amount of time and effort. This is why a clear, comprehensive indicator for assessing disease risk is needed. The most useful tool for this purpose is "genetic testing," which can examine the possibility of many hereditary diseases at once.

DNA Score and DNA Matching ― Visualizing Genetic Risk

What Is the DNA Score

seeDNA Co., Ltd. offers a service called the "DNA Score," which examines the largest number of gene loci in the industry — 1,528 locations — allowing you to check disease risks and other factors related to DNA regions as concrete numerical values [ref:4]. While conventional genetic testing has mainly focused on examining only a small number of gene mutations related to specific diseases, the DNA Score allows for a more comprehensive assessment of genetic risk by comprehensively analyzing a large number of gene loci.

In recent genetic research, genome-wide association studies (GWAS) have identified numerous disease-related gene loci, and a method called the "polygenic risk score (PRS)," which comprehensively scores these loci, has been attracting attention [ref:5]. The DNA Score is a service built on the foundation of these latest genetic insights.

What Is DNA Matching

seeDNA also offers a service called "DNA Matching," which allows you to estimate the health status of a future child by sharing your DNA Score with your partner. DNA Matching compares the DNA Scores of two people to check whether both are carriers of the same recessive genetic disease, allowing you to understand in advance the risk of a child developing a hereditary disease.

This kind of "carrier screening" is already widely established overseas, and the Tay-Sachs disease screening program within the Ashkenazi Jewish community is well known as a successful example that dramatically reduced the incidence of the disease [ref:3].

Benefits of Using DNA Score and Matching

1. Understand your own genetic characteristics ― By analyzing as many as 1,528 gene loci, you can comprehensively understand which diseases you may be a carrier for.
2. Check genetic compatibility with your partner ― DNA Matching lets you check whether both partners are carriers of the same disease gene, allowing you to estimate the genetic risk to a future child.
3. Apply it to future planning ― Understanding the risk in advance allows you to take concrete action, such as seeking genetic counseling or considering your family planning.

Combine with Genetic Counseling

The results of genetic testing should not be judged by numbers alone; it is recommended that they be interpreted together with a genetic counseling specialist. Having a gene mutation does not necessarily mean the disease will develop, since penetrance and environmental factors also affect whether or not a condition manifests. To correctly understand the results of your DNA Score and DNA Matching and to consider appropriate courses of action, we encourage you to actively consult with a specialist.

Why not check your genetic compatibility with your partner through DNA Matching as early as possible, understand the likelihood of passing on a hereditary disease to your children, and use that knowledge to plan a brighter future together?

Frequently Asked Questions

Q1. What is the difference between dominant inheritance and recessive inheritance?

A. Dominant inheritance is a form of inheritance in which the disease develops when a person has just one copy of the disease-causing gene mutation. Recessive inheritance, on the other hand, only develops when both the paternal and maternal alleles carry the mutation. In recessive inheritance, a "carrier" who has only one copy of the mutation does not develop the disease, so it can be passed on to the next generation unknowingly.

Q2. What does "carrier" mean?

A. A carrier is a person who has just one copy of the gene mutation that causes a recessive genetic disease, but does not develop the disease themselves. A child born to two carrier parents has a 25% chance of developing the disease.

Q3. How many genes does the DNA Score examine?

A. seeDNA's DNA Score examines 1,528 gene loci, the largest number in the industry. This makes it possible to comprehensively evaluate genetic risks related to numerous diseases at once.

Q4. What can I learn from DNA Matching?

A. DNA Matching compares the DNA Scores of you and your partner to check whether you are both carriers of the same recessive genetic disease. This allows you to understand in advance the risk that a future child may develop a particular hereditary disease, and to take appropriate action, such as seeking genetic counseling.

Q5. Is there a genetic concern with marriage between cousins?

A. Marriages between relatives, such as cousins, carry a higher probability of inheriting the same recessive gene mutation from a common ancestor. As a result, the statistical risk of having a child with a recessive genetic disease is higher compared to unrelated couples. However, this does not mean the disease will definitely develop, and it is important to properly assess the risk through genetic testing and counseling.

Q6. Does "dominant" mean "superior"?

A. No, "dominant" means that a genetic trait tends to appear on the surface, not that the trait is biologically superior. To prevent this misunderstanding, the Genetics Society of Japan recommended changing the terminology in 2017.

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