Lesson Video: Medical and Genetic Screening | Nagwa Lesson Video: Medical and Genetic Screening | Nagwa

Lesson Video: Medical and Genetic Screening Biology • First Year of Secondary School

In this video, we will learn how to recall some examples of diseases that can be genetically or medically screened for, and explain why genetic screening is offered to certain individuals.

10:24

Video Transcript

In this video, we will learn about some diseases that a person or a couple may be genetically or medically tested for. We will learn about different types of genetic tests that are carried out before a child is conceived or born. We will also understand why some people and couples will be offered genetic or medical screening.

Diseases are an everyday part of human life, whether it’s due to pesky pathogens infecting our bodies or genetic disorders that can be inherited. Humans have to live alongside a range of diseases. One of the things we can do to limit the spread of disease and help understand them more is to screen people for certain diseases. Screening is a term that’s used to refer to the process of studying a person’s DNA or general health to identify infectious diseases, genetic disorders, or any susceptibility to them.

Let’s start by having look at genetic screening. Genetic screening works by studying a person’s DNA. DNA, or deoxyribonucleic acid, is our genetic material. It controls our characteristics, such as eye color and natural hair color, and is also the unit of inheritance. A section of DNA that codes for a particular characteristic is called a gene. Sometimes there’s mistakes in these genes, called mutations, that can cause certain diseases. For instance, a mutation in the HEXA gene on chromosome 15 can cause Tay–Sachs disease. Tay–Sachs is a genetic disorder which causes the destruction of nerve cells in the brain and spinal cord. Children with Tay–Sachs tend to have serious seizures, problems with their movement, and unfortunately it is highly likely to result in an early death. Tay–Sachs is caused by a recessive allele. This means a person must inherit two copies of the allele to inherit the disease.

Let’s take a closer look at how this might happen. If someone has a recessive allele for Tay–Sachs but also has the corresponding dominant allele that doesn’t cause Tay–Sachs, then they are referred to as a carrier. This means that they have the allele that causes a certain disease or disorder, but they don’t have the disease themselves. We can display this as a written genotype using the letters uppercase T for the nonmutated allele and lowercase t for the allele that causes Tay–Sachs.

Let’s imagine this person has children with another person who is also a carrier. When the male’s sperm fertilizes the female’s egg, they pass on their alleles to any offspring they have. If the offspring inherit the uppercase T and uppercase T allele, then the child will be unaffected and not a carrier. If they inherit an uppercase T and a lowercase t, the child will be a carrier. Likewise, if they inherit the lowercase t and uppercase T, like this, the child will also be a carrier. And if they inherit the lowercase t and lowercase t, then the child will have Tay–Sachs.

By carrying out genetic screening on potential parents, we can better understand the risk they have of passing genetic disorders on to their offspring. This then allows them to make informed choices and prepare themselves for any potential diseases or disorders that may arise in their children. Now let’s take a look at some different types of genetic screening.

Carrier testing is a form of genetic screening. It is offered to people who have a family history of genetic disease but they themselves do not display symptoms. This type of screening would be best for a couple that has a family history of a disease like Tay–Sachs, which we saw in the previous example.

Preimplantation testing is another type of genetic screening. It can be used to test embryos that are being used in IVF, or in vitro fertilization. This is done before they are placed in the mother’s uterus. This is why it’s preimplantation. Again, this will most likely be offered to couples who have a family history of genetic disorders.

Prenatal testing is carried out on pregnant mothers before the baby is born. It’s most likely to be offered to expectant mothers that are in at-risk groups. For example, the chances of a baby developing the chromosomal disorder Down syndrome increases with age. So expectant mothers over the age of 35 are often offered a prenatal test for Down syndrome.

Newborn testing is carried out on newborn babies. This is often to screen genetic disorders that can be treated early in life. This way, these disorders can be treated before developing into something more debilitating. An example of this is the genetic disorder PKU. If left untreated, PKU can lead to severe brain damage. But if identified and treated early in life, the babies will go on to lead a PKU-free life.

Finally, presymptomatic testing can be used for people that have a family history of a certain disorder that they are not displaying symptoms for yet. This type of test is most common for disorders that tend to develop later on in life. For example, Huntington’s disease is a neurological disease which usually starts to display its symptoms when a person is in their 40s. By being tested earlier for Huntington’s when they are younger, a person may be able to prepare themselves for this disease if it will affect them later on in life.

It’s important to note that while genetic screening is useful and informative, it is not 100 percent certain. And as some genetic disorders still have no cure, the choice to have genetic screening is a personal choice that must be made by the individuals involved.

Now let’s have a quick look at medical screening. Medical screening for couples planning on having children is often used to prevent the transmission of infectious disease rather than genetic or inherited disease. This helps prevent the transmission of infectious disease between couples and between parents and their children. Types of diseases that can be tested for include sexually transmitted diseases like HIV or hepatitis or others. These can potentially be passed on to the fetus or newborn, so screening is very important.

Now that we’ve learned more about genetic and medical screening, let’s try a practice question.

All of the individuals described below are planning on having children in the near future. Person A has a grandparent who is an identical twin. Person B has a family history of thalassemia, a disorder affecting the hemoglobin of the blood. Person C lives in a small community and is marrying their first cousin. And person D already has two girls and would like a boy. Which of the people listed above would most likely be offered genetic screening?

Genetic screening is the process by which a person’s DNA is studied to identify any genes that could cause a genetic disorder. It is commonly offered to those with a family history of a specific illness or disease. Genetic screening can be carried out either before a couple tries to conceive or during pregnancy. For high-risk parents or those that are related, these tests are offered in the prepregnancy stage. One type of genetic screening is called carrier screening. This is used for people with a history of a genetic disease but who do not have symptoms. So it is unclear if they carry the allele for that disease. We can see that this description applies to one of our options. Person B has a family history of thalassemia.

Genetic screening may also be offered to those that live in isolated communities or communities that have a history of a particular genetic disorder. This is because, typically, these communities are made up of family groups and individuals are highly related. This means that if this grandparent was a carrier for a recessive genetic disease like Tay–Sachs, they could pass this on to their children. Their children, shown here, are now carriers for the disease. But they could pass the allele on to their own children. If these two individuals who are cousins were now to have their own children, they have a much higher risk of passing on two recessive alleles to their children. This means that their offspring are much more likely to inherit Tay–Sachs disease. This means that genetic testing is likely to be offered to another one of our individuals, person C, who lives in a small community and is marrying their first cousin.

Genetic screening is only offered to those who are at risk of passing on genetic diseases to their offspring. This helps prevent the spread of disease and allows parents to prepare themselves mentally, physically, and financially for having a child with a genetic disorder. It is not offered to people who would like to choose the sex of their child, so we can exclude person D. And we can also exclude person A, as genetic screening will not be offered to people who are expecting or who would like twins.

So the correct answer to which people would be offered genetic screening is person B and person C.

Now let’s take a moment to go over the key points that we covered in this video. Genetic screening in conception and pregnancy is used to limit the inheritance of genetic disorders and diseases. Different groups or individuals may be recommended for genetic screening based on their family history or other factors. Some examples of genetic disorders that can be screened for include Tay–Sachs, which is screened for before pregnancy; Down syndrome, which is screened for during pregnancy; and Huntington’s disease, which is screened for after pregnancy and typically much later in life. Another type of screening is medical screening. And this helps prevent the spread of infectious diseases like HIV and hepatitis.

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