Monday, July 15, 2024
General Agriculture

Animal DNA Tests and Segregation Analysis for Genetic Disorders

Animal DNA tests are diagnostic tests that are used to confirm a diagnosis in a patient or animals with symptoms suggesting a particular genetic disease. For example, in human, a person with a movement disorder may be tested for Huntington’s disease.

Almost every cell in every living organism contains a cell-nucleus that holds the pairs of chromosomes that make up the genetic material. Each chromosome has within it the DNA (deoxyribonucleic acid) that makes up hundreds of thousands of genes.

Many of these genes make proteins that have a number of roles in the body. Some proteins are structural and make up tissues like bones and muscles. Proteins called enzymes are involved in chemical reactions like breaking down the ingested food.

While others are like little messengers that send signals around the system, these proteins are known as hormones. All individuals within a species share the same set of genes but the precise DNA sequence of these genes differs slightly between individuals (by about 0.1-0.2%).

While these differences account for things like differing hair, eye and skin colour, they can also be the cause of genetic disease or disease susceptibility. A disease causing change in the DNA of a gene is called a mutation. DNA or genetic tests are such procedures used to uncover mutation or alterations in genes that could lead to genetic disorders.

Many disorders in animals are observed more frequently in certain breeds and within breeds more often in the same families. Familiarity is assumed for a disorder when families are observed with more than one affected family member.

Familial disorders may have a genetic contribution. The same is often claimed for disorders which show a breed disposition. On the other hand, genetically caused diseases may not necessarily lead to breed differences in incidence but will contribute to variation among families within breeds.

A useful starting point for answering the question whether a disorder is inherited is by drawing pedigrees to provide an initial impression of the distribution of affected and non-affected animals and how frequently the disorder is transmitted from one generation to the next.

Animal DNA Tests

These are diagnostic tests that are used to confirm a diagnosis in a patient or animals with symptoms suggesting a particular genetic disease. For example, in human, a person with a movement disorder may be tested for Huntington’s disease.

The genetic information from the test is useful in the treatment, management and genetic counseling of the patient. Some genetic tests are used even when symptoms of a disease are not seen, but the genetic information may help in predicting if the person is at risk of developing, or are susceptible to a particular disease. Genetic screening tests are;

Prenatal testing: This type of testing is offered during pregnancy if there is an increased risk that the baby or progeny will have a genetic or chromosomal disorder. In some cases, prenatal testing can lessen a couple’s uncertainty or help them make decisions about a pregnancy. It cannot identify all possible inherited disorders and birth defects.

A good example of this is the screening in human is for Down syndrome in women over 35. Screening for Down syndrome is usually carried out by amniocentesis or chorionic villus sampling at 14 – 20 weeks of gestation. Prenatal testing is used to detect changes in a fetus’s genes or chromosomes before birth.

New born screening is used just after birth to identify genetic disorders that can be treated early in life.

In humans, millions of babies are tested each year in the United States and Europe especially for phenylketonuria (a genetic disorder that causes intellectual disability if left untreated) and congenital hypothyroidism (a disorder of the thyroid gland) and cystic fibrosis (CF).

A blood sample is taken from the newborn; this blood sample is then sent to a laboratory for testing.

Carrier screening is offered to parents-to-be so that they can test if they are carriers for diseases such as cystic fibrosis (CF).Carrier testing is used to identify people who carry one copy of a gene mutation that, when present in two copies, causes a genetic disorder.

This type of testing is offered to individuals who have a family history of a genetic disorder and to people in certain ethnic groups with an increased risk of specific genetic conditions.

If both parents are tested, the test can provide information about a couple’s risk of having a child with a genetic condition.

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Diagnostic testing is used to identify or rule out a specific genetic or chromosomal condition. In many cases, genetic testing is used to confirm a diagnosis when a particular condition is suspected based on physical signs and symptoms.

Diagnostic testing can be performed before birth or at any time during a person’s life, but is not available for all genes or all genetic conditions. The results of a diagnostic test can influence a person’s choices about health care and the management of the disorder.

Preim plantation testing, also called preimplantation genetic diagnosis (PGD), is a specialized technique that can reduce the risk of having a progeny with a particular genetic or chromosomal disorder.

It is used to detect genetic changes in embryos that were created using assisted reproductive techniques such as in-vitro fertilization. In-vitro fertilization involves removing egg cells from a woman’s ovaries and fertilizing them with sperm cells outside the body.

To perform preimplantation testing, a small number of cells are taken from these embryos and tested for certain genetic changes. Only embryos without these changes are implanted in the uterus to initiate a pregnancy.

Animal DNA Tests and Segregation Analysis for Genetic Disorders

Predictive testing can identify mutations that increase a person’s risk of developing disorders with a genetic basis, such as certain types of cancer.

Predictive and pre symptomatic types of testing are used to detect gene mutations associated with disorders that appear after birth, often later in life. These tests can be helpful to people who have a family member with a genetic disorder, but who have no features of the disorder themselves at the time of testing for example in dairy industry to guard against occurrence of mastitis.

Presymptomatic testing can determine whether a person will develop a genetic disorder, such as hereditary hemochromatosis (an iron overload disorder), before any signs or symptoms appear.

The results of predictive and presymptomatic testing can provide information about a person‟s risk of developing a specific disorder and help with making decisions about medical care.

Forensic testing uses DNA sequences to identify an individual for legal purposes. Unlike the tests described above, forensic testing is not used to detect gene mutations associated with disease.

This type of testing can identify crime or catastrophe victims, rule out or implicate a crime suspect, or establish biological relationships between people (for example, paternity).

Methods and Techniques Used In Animal Genetic Testing

Before a genetic test is carried out, clinical examination is carried out and a detailed family history gotten. This will help in working out which gene may be responsible for the disease in question.

In human, the patient will be referred to a genetic counsellor who can inform them about everything that is involved with genetic testing. The genetic counsellor can tell you what it means to have a particular genetic change and how this can affect individual or the family.

In the case of animals, these will form a basis of whether to cull the animal or to be applying symptomatic treatment.

Almost all genetic tests require a DNA sample from the patient; this is usually obtained by either a blood sample or mouthwash (buccal swab) which is then taken to a genetic testing lab for analysis. A number of techniques are used in the process of genetic testing, these include:

Polymerase Chain Reaction (PCR) and DNA Sequencing

The polymerase chain reaction (PCR) is a method of amplifying (copying) a small amount of DNA to a larger amount so that it can be analyzed closely.

The genetic code of the DNA can be determined by a method called “DNA sequencing‟. This then allows scientists to determine whether or not there is a change or mutation present in a gene of interest.

Indirect Gene Tracking (Linkage Analysis)

If the gene associated with a hereditary disease in a family is not known then linkage analysis can help in identifying the responsible gene. The technique is based on the fact that special DNA sequences that flank particular genes will travel with the gene when passed from parent to child.

These DNA sequences are called “polymorphic markers‟ or “polymorphic repeat sequences‟. The closer that one of these markers is to gene the more likely it is that it is travelling with the gene.

If a particular polymorphic marker is found only in members of a family with a particular disease then it is likely that a gene located near the marker is associated with the disease.

Advantages of Genetic Screening

Through genetic testing we may be able to screen populations for diseases in order to better diagnose, treat and prevent disease. Reducing the incidence of disease has major impacts on and is of great importance to:

Families: When a child is born with a particular disease, there may be no apparent family history. With simple genetic testing for carrier status of the parents, the birth of a child with disease could have been prevented.

Health resources: The birth of a child with a genetic disorder adds stress to health systems and resources. Carrier screening programs could act as important components of the medical system in preventing disease through offering people informed reproductive choices.

Disadvantages of Genetic Testing

Many people would rather not know if they have a pre-disposition to a particular disease. People may have enough stress in their lives already to have to deal with an oncoming genetic disease, or that they are a carrier of a particular disease mutation that may affect their future children.

There is also the possibility of some sort of negative stigma attached to having a carrier status for a particular disease.

If the genetic cause of a disease is identified in a patient, it does not necessarily guarantee that there is a cure for the disease. A treatment or therapy may not yet have been developed. The identification of a disease gene means a large step towards finding a cure; it is often of no great immediate benefit to the patient.

Ethical Issues Associated With Genetic Testing

As carrier screening would involve the screening of a possibly asymptomatic population, it inevitably raises a number of ethical issues in terms of consent, privacy and education, which need to be considered. It is important that all persons involved are appropriately educated, their consent obtained and the confidentiality of their genetic information upheld.

Prenatal genetic screening can inform parents of the health status of their unborn child. In the case of a prenatal diagnosis of disease, parents are able to assess their options and make decisions accordingly.

Foetal genetic testing does however raise the issue of abortion, often a particularly sensitive and controversial matter.

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Benadine Nonye is an agricultural consultant and a writer with several years of professional experience in the agriculture industry. - National Diploma in Agricultural Technology - Bachelor's Degree in Agricultural Science - Master's Degree in Science Education - PhD Student in Agricultural Economics and Environmental Policy... Visit My Websites On: 1. - Your Comprehensive Practical Agricultural Knowledge and Farmer’s Guide Website! 2. - For Effective Environmental Management through Proper Waste Management and Recycling Practices! Join Me On: Twitter: @benadinenonye - Instagram: benadinenonye - LinkedIn: benadinenonye - YouTube: Agric4Profits TV and WealthInWastes TV - Pinterest: BenadineNonye4u - Facebook: BenadineNonye

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