Genetics 101
Genes are the fundamental units of heredity that provide the instruction for a particular trait, such as hair or eye color. Genes are made up of a chemical called deoxyribonucleic acid, or DNA. Each gene contains the information needed for making a specific protein, and each protein has a particular function in the body, such as making enzymes for biochemical processes.
Genes are packaged into structures called chromosomes. Chromosomes come in pairs, and there can be hundreds and even thousands of genes on one chromosome. Every cell in the body has a total of 46 chromosomes, each with 23 pairs. Half of a person’s chromosomes come from the egg and the other half from sperm. The first 22 pairs of chromosomes are referred to as autosomes because they are the same between males and females. The 23rd, and final, pair are called sex chromosomes because these determine biological sex. Males have an X and a Y chromosome while females have two X chromosomes.
People have two copies of every gene, one inherited from the egg and one from the sperm. Single gene disorders arise when one or both copies of a specific gene have a change, called a disease-causing variant.
A dominant disorder can occur when a person has a change, or disease-causing variant, in one copy of the gene associated with the condition. Dominant conditions are often inherited from an affected parent. Someone with a dominant condition (or variant that may lead to a dominant condition) has a 50% chance of passing down the changed copy of the gene and a 50% chance of passing down the functional copy of the gene with each pregnancy.
Sometimes, a disease-causing variant appears in an individual even though neither parent has that variant. Such occurrences, referred to as “de novo,” result from a new, random change in a sperm or egg cell, or in the fertilized egg itself.
A recessive disorder occurs when a person has a change, or disease-causing variant, in both copies of the gene associated with the condition. To have changes in both copies of the gene, one must be inherited from the egg and one from the sperm.
Someone with a disease-causing variant in one copy of a recessive gene is known as a carrier. Carriers are typically healthy and do not have the genetic condition. However, two partners who are carriers for the same recessive disorder are at risk for having a child with the condition. In each pregnancy, a carrier couple has a 25% chance of having a child with the condition, a 50% chance of having a child who is a carrier, and a 25% of having a child who is neither affected or a carrier.
Because both parents must carry the condition for there to be risk to a child, recessive conditions can hide in families for generations. Carrier screening prior to or early on in pregnancy can help you learn what genetic changes you carry.
An X-linked condition can occur when a person has a change, or disease-causing variant, on their X chromosome. Males have an X and Y chromosome while females have two X chromosomes. In most cases, females with a disease-causing variant in an X-linked gene are not affected because they have a second functioning copy of the gene. When X-linked conditions occur in females, symptoms are typically milder. Since males have only one X chromosome, they have no such ‘backup’ copy and are therefore more likely to have an X-linked condition.
Because females can have a disease-causing variant in an X-linked gene without displaying symptoms, they are more likely to be carriers of X-linked conditions than males. As a result, X-linked conditions are usually passed down from carrier mothers to sons.
Jewish Genetic Disorders
The term “Jewish genetic disorders” describes a group of conditions that are more common among Jews of Ashkenazi (Central, and Eastern European) descent. Although these conditions can affect anyone, they appear in those of Ashkenazi Jewish descent more frequently than in the general population, sometimes as much as 20 to 100 times more frequently.
While these genetic conditions vary in severity and age of onset, most of the Jewish genetic disorders are debilitating, and some are fatal. Many of the conditions lack effective treatment at this time. Genetic counseling and carrier screening are therefore invaluable in planning for a family.
Certain genetic conditions tend to be more common among individuals of Jewish descent due to the founder effect. Most of today’s Ashkenazi Jews likely descended from a group of only a few thousand individuals or “founders” who immigrated to Eastern Europe during the Diaspora. As a result, variants, or changes, that started in perhaps only a few individuals in the founder population have become more frequent over time as the Jewish population reproduced and grew.
Yes. Genetic disorders that are common among Sephardic Jews vary based on country of origin. Though Jewish genetic disorders vary in severity and age of onset, most are debilitating, and some are fatal. Many of the conditions are rare and lack effective treatment at this time. Genetic counseling and carrier screening are therefore invaluable in planning for a family.
Many carrier screening panels include conditions more common in the Sephardic Jewish community, however, they are not all-encompassing. All persons of Ashkenazi and/or Sephardic Jewish ancestry should consider expanded genetic testing and counseling in order to address possible inheritable conditions.
Approximately one in four Jews is a carrier for one of 100 “Jewish” genetic conditions included in our carrier screening panel. More than 80% of our screening program participants are carriers of at least one of the 267 genetic conditions on our expanded carrier screening panel.
About Jewish Genetic Disorders
Get information and resources about genetic conditions more common in the Jewish community.
Genetic Disorders Included on Our Screening Panel
Our screening panel tests for 245 recessive conditions, including over 100 conditions more common among people with Ashkenazi and Sephardic Jewish ancestry. Our panel also includes an additional 21 X-linked conditions for all individuals and Fragile X syndrome for individuals assigned female at birth. You can learn more about each of the conditions on the panel by browsing or searching the database linked below.
About Carrier Screening
Planning for a family? Our affordable, accessible carrier screening program allows most participants to get screened from home.
Articles and Events
Should I Get Screened Again?
While our DNA doesn’t change, technology does. Check in with your doctor or a contact the Sarnoff Center's genetic counselor to learn whether you should consider re-screening prior to pregnancy.
Fragile X Awareness
July is Fragile X Awareness Month. Fragile X syndrome is a condition that leads to intellectual disability and is prevalent in the Ashkenazi Jewish population.
Proactive Choices for You and Your Baby’s Health
Any parent-to-be wants to provide their child with a healthy life, and prenatal genetic tests can help. There are a wide variety of genetic tests available, including carrier screening, diagnostic testing, and aneuploidy screening.
