Introduction:
Medical genetics can be defined as a stream of medicine that includes the diagnosis as well as management of hereditary disorders (a disease that occurs due to harmful changes in genes). According to Mendelian inheritance, gene transmission occurs from generation to generation. Genetics can be divided into biochemical genetics and clinical genetics. In biochemical genetics, there is a relative difference between protein change and metabolism. It involves the study of the causes of many heritable diseases, such as thalassemia and sickle cell disease. Clinical genetics deals with the study of chromosomal aberrations. Major advances in prenatal diagnosis, newborn screening, and genetic testing play a vital role in day-to-day primary care. Human genetics is changing the picture of human disease. There is a hope that genetics will provide therapeutic changes and play a role in medicine and primary care. This article will review the principle of genetics, which is required for understanding the application of genetics in medical practice.
What Is Gene and Human Genome?
Gene is the basic unit of hereditary, and it originated in the 20th century. It is composed of protein. Human Genome is made up of DNA (deoxyribonucleic acid). DNA forms a double helix which is made up of chemical bases. Sugar phosphate is the backbone of DNA attached to a set of pyrimidine and purine bases. These substances are held together by hydrogen bonds. The strands of DNA separate during DNA replication. DNA replication is the process of making its own copy which is essential for cell growth. It allows the cell to grow with an equal number of DNA. DNA contains the information necessary for replication. The sequence of bases in the DNA determines the structure of the protein. Protein consists of a chain of amino acids. A triplet of bases (codons) represents amino acids in DNA. During replication, the base sequence of one strand of DNA is copied into a complementary RNA (mRNA), which is in turn translated on the ribosome into protein. Transcription refers to copying a gene's DNA sequence into the messenger RNA (mRNA). The mature mRNA is exported to the cytoplasm for translation into protein. During translation, the mRNA sequence is read into the amino acid sequence of a protein. This is the life of the DNA.
The expected human genome is estimated at around 1 lakh, and there are three billion base pairs of DNA, and the average gene is approximately 30,000 bases. Humans have two copies of every gene except those carried on the sex chromosome (one copy from each parent). Allele refers to copies of genes. The gene is located at a specific location in the human which is called the locus. The locus constituent of the genotype and the resulting physical characteristic from the gene is called the phenotype. Human cells consist of 46 chromosomes, including 22 pairs of non-sex chromosomes and two sex chromosomes (XX in females, XY in males).
What Is Medical Genetics?
Genetics is a branch of Biology that includes the structure, location, and abnormalities of the genes. Medical genetics is the expression of abnormal genes or gene combinations in the production of disease. Genetics provides a pattern of inheritance between generations. However, there are harmful changes in our genes that will cause genetic disorders. It can be of many types, such as a single gene mutation, multiple gene mutation, and chromosomal disorder. Mutation refers to an alteration in the structure of the gene. In monogenic disorder, changes occur in a single gene. In complex disorder, it is also called multifactorial, is caused due to chemical exposure, diet, certain medication, and of tobacco or alcohol use. In chromosomal disorders, there is a defect in the structures that hold the gene or DNA. Medical genetics plays a vital role in chromosomal diseases, which focuses on the appropriate diagnosis and treatment.
What Are Genetic Disorders?
Genetic disorders refer to the wrong amount of genetic material due to mutation (a harmful change to a gene) that affects the gene. Sometimes the genes that are received from biological parents may be changed due to any issues in the DNA called a mutation. These harmful changes in genes cause genetic disorders. In some cases, the symptoms can be seen at birth, and in other cases, it can be seen in later years.
There are many genetic disorders, such as:
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Down Syndrome (Trisomy 21): A chromosomal disorder caused by the presence of an extra copy of chromosome 21, resulting in intellectual disabilities and distinct physical features.
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Cystic Fibrosis: A genetic disorder that affects the production and flow of mucus in the lungs and digestive system, leading to respiratory and digestive problems.
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Huntington's Disease: A neurodegenerative disorder caused by a mutation in the huntingtin gene, leading to the progressive deterioration of brain cells, resulting in movement, cognitive, and psychiatric symptoms.
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Sickle Cell Disease: A group of inherited blood disorders characterized by abnormal hemoglobin, causing red blood cells to become sickle-shaped and leading to episodes of pain, organ damage, and anemia.
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Hemophilia: A bleeding disorder characterized by the inability of blood to clot properly due to defects in specific clotting factors, resulting in prolonged bleeding and easy bruising.
What Are the Principles of Medical Genetics?
The principles of medical genetics are a set of fundamental concepts and guidelines that help in understanding the inheritance and occurrence of genetic disorders in individuals and families. These principles are the foundation of medical genetics and play a crucial role in diagnosing, managing, and treating genetic conditions.
Here are some key principles of medical genetics:
1. Mendelian Inheritance - The Mendelian theory provides information about the gene which causes specific disorders so that it is related to medical genetics. According to the Mendelian concept, the inheritance of traits depends on passing all of the genes. The Mendelian theory of genetics is based on three principles of inheritance. These theories describe the transmission of genetic traits. Every single unit or gene is independent of its action in any individual genome (complete set of genetic material present in DNA). Traits can be divided into dominant or recessive genes. Dominant genes are more likely to transmit down to the next generations, and recessive genes are prone to be less transmitted to another generation.
Some examples of Mendelian traits include.
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Red-green colorblindness (color deficiency in humans)
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Hemophilia (reduced blood clotting capacity)
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Albinism (absence of pigment in skin and hair by birth)
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Dimples on cheek (indentations in facial muscle).
2. Single Gene Mutation -Sometimes, single gene mutation occurs, which causes genetic disorders.
3. Multifactorial Inheritance - Most disorders caused by single gene changes are rare. Genetic factors also contribute to the etiology of common disorders, but here multiple genes interacting with one another and with environmental factors are required to cause the phenotype. This is referred to as multifactorial inheritance.
4. Gene Mutation - Alterations in the DNA coding sequence are referred to as mutations. Mutations can lead to complete failure of expression of a gene, aberrant regulation, or abnormal function of protein products of the gene.
What Is the Role of Genetic in the Medical Field?
The following are the role of genetics in medical field:
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It involves the study of disease with inheritance in families.
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It states about the molecular mechanism by which genes cause disease.
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It helps in locating the position of affected genes at specific chromosomes.
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It also involves the diagnosis and treatment of disease using these genetics.
Conclusion:
Multiple family members are affected and may experience different types of disease. Single-gene diseases and complex multifactorial diseases are both common phenomena of genetic heterogeneity (changes at two or more genetic locations but producing the same phenotypes). These effects can be due to different mutations in the same gene, resulting in similar phenotypes. Multifactorial inheritance and Mendelian inheritances are the basic principles of genetics. The role of genetics in the medical field is discussed above. There is a hope that genetics will bring therapeutic changes.
