On this page, we explain how hereditary diseases are passed from one generation to another.
Hereditary diseases, often termed as genetic disorders, are conditions that arise due to abnormalities or mutations in the DNA. These mutations can be inherited from one or both parents, leading to the manifestation of specific conditions in their offspring. Understanding how these diseases transition from one generation to the next requires delving deep into genetics, the study of genes and their roles in inheritance.
How Hereditary Diseases are Passed From One Generation to Another
Hereditary diseases are passed from one generation to another through genes, which are segments of DNA carrying genetic instructions. These genes are located on chromosomes, and when there’s a mutation or abnormality in the DNA, it can lead to a genetic disorder. Depending on the mode of inheritance—such as autosomal dominant, autosomal recessive, X-linked, or mitochondrial—these mutations can be inherited from one or both parents, resulting in the manifestation of the disease in the offspring. Simply put, the combination of genes received from both parents determines whether an individual might inherit a hereditary disease.
Scenario: Passing of Hereditary Disease in James’ Family
- Step 1: Family Background James’ father had a hereditary disease called Huntington’s, which is an autosomal dominant disorder. This means only one copy of the faulty gene from one parent is enough to inherit the disorder.
- Step 2: Gene Mutation In James’ father’s DNA, there was a mutation in the gene responsible for Huntington’s disease. This mutated gene was located on one of his autosomal (non-sex) chromosomes.
- Step 3: Conception When James was conceived, he received one set of chromosomes from each parent. From his father, there was a 50% chance he would inherit the chromosome with the mutated gene.
- Step 4: Receiving the Mutated Gene Unfortunately, James did inherit the chromosome carrying Huntington’s mutation from his father. Because Huntington’s disease follows an autosomal dominant inheritance pattern, inheriting just one copy of the mutated gene from one parent means James will develop the disease.
- Step 5: Manifestation As James grows older, even though he received only one copy of the faulty gene, the disease starts to manifest, because that’s the nature of autosomal dominant disorders. The exact age at which symptoms appear might vary, but the inherited mutation ensures the onset of the disease at some point in his life.
The Basics of Genetics
- DNA and Genes: DNA, or deoxyribonucleic acid, is the molecule that carries the genetic instructions for the development, functioning, growth, and reproduction of all known living organisms. Genes are segments of DNA that carry the code for a specific protein that functions in one or more types of cells in the body.
- Chromosomes: Humans have 46 chromosomes arranged in 23 pairs. One chromosome from each pair comes from the mother, and the other comes from the father. It’s these chromosomes that carry genes, which in turn carry our genetic information.
Modes of Inheritance
- Autosomal Dominant: Only one mutated copy of the gene is required for a person to be affected by an autosomal dominant disorder. An affected person usually has one affected parent. Examples include Huntington’s disease and Marfan syndrome.
- Autosomal Recessive: Two copies of the gene must be mutated for a person to be affected by an autosomal recessive disorder. Both parents carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition. Cystic fibrosis and sickle cell anemia are examples of autosomal recessive disorders.
- X-linked: Genes that are carried by the X chromosome are called X-linked. Males have one X and one Y chromosome (XY) and females have two X chromosomes (XX). Thus, males are more frequently affected by X-linked disorders. Examples include hemophilia and Duchenne muscular dystrophy.
- Mitochondrial Inheritance: This involves mutations in the DNA of mitochondria, which are tiny structures within cells that convert food into energy. Since egg cells, but not sperm cells, keep their mitochondria during fertilization, only mothers can pass on mitochondrial conditions to their children. An example is Leber’s hereditary optic neuropathy.
Facts About Hereditary Diseases
- Not Always Apparent: Just because a person carries a mutation for a hereditary disease doesn’t mean they will exhibit symptoms. They might be carriers without any manifestation of the disease.
- Environmental Triggers: Sometimes, a combination of genetics and environment can lead to hereditary diseases. For instance, a person might have a genetic predisposition to a certain type of cancer, but an environmental factor like smoking triggers its onset.
Theories and Advancements
- Gene Therapy: Scientists are studying the potential of replacing faulty genes with healthy ones as a treatment for genetic disorders.
- Epigenetics: This is the study of how behaviors and environment can cause changes that affect the way genes work. Unlike genetic changes, epigenetic changes are reversible and do not change DNA sequence, but they can change how the body reads a DNA sequence.
- CRISPR-Cas9: A revolutionary gene-editing tool that allows for precise changes to DNA, offering potential cures to many hereditary diseases.
17 Hereditary Diseases List
Hereditary diseases, also known as genetic disorders, arise due to abnormalities in an individual’s DNA. These abnormalities can either be inherited or result from DNA changes during an individual’s life. Here’s a list of some hereditary diseases:
- Cystic Fibrosis: A condition affecting the respiratory and digestive systems, caused by mutations in the CFTR gene.
- Huntington’s Disease: A neurodegenerative disorder leading to physical and mental disabilities, caused by mutations in the HTT gene.
- Sickle Cell Anemia: A blood disorder where red blood cells assume a sickle shape, leading to various complications. It results from a mutation in the HBB gene.
- Hemophilia: A bleeding disorder where blood doesn’t clot properly, due to mutations in the F8 or F9 genes.
- Duchenne Muscular Dystrophy: A muscle degeneration and weakness disorder due to mutations in the DMD gene.
- Tay-Sachs Disease: A fatal disorder that affects nerve cells in the brain, caused by mutations in the HEXA gene.
- Polycystic Kidney Disease: A condition where numerous cysts form in the kidneys, leading to kidney dysfunction. It’s caused by mutations in the PKD1 or PKD2 genes.
- Marfan Syndrome: A disorder affecting the body’s connective tissue, caused by mutations in the FBN1 gene.
- Down Syndrome: Caused by an extra copy of chromosome 21.
- Fragile X Syndrome: A genetic condition causing a range of developmental problems, including cognitive impairment and learning disabilities, due to mutations in the FMR1 gene.
- Turner Syndrome: A condition in females where one of the X chromosomes is missing or partially missing.
- Phenylketonuria (PKU): A metabolic disorder caused by mutations in the PAH gene, leading to an inability to break down the amino acid phenylalanine.
- Albinism: A group of inherited disorders characterized by little or no production of the pigment melanin, resulting from various gene mutations.
- Neurofibromatosis: A condition causing tumors to form in the nervous system, typically resulting from mutations in the NF1 or NF2 genes.
- Achondroplasia: A form of short-limbed dwarfism resulting from mutations in the FGFR3 gene.
- Rett Syndrome: A rare genetic neurological and developmental disorder that affects the way the brain develops, primarily caused by mutations in the MECP2 gene.
- Thalassemia: A blood disorder causing reduced hemoglobin and fewer red blood cells than normal due to mutations in the HBB gene.
This list is by no means exhaustive, as there are thousands of known hereditary diseases. Some are common, while others are rare. Genetic testing and counseling can provide information on the risks and implications of many hereditary diseases.
Hereditary diseases are passed from one generation to the next through our genes, which are encoded in DNA and organized into chromosomes. While the mechanisms of inheritance are understood in many cases, ongoing research promises even more advanced insights and potential treatments for these conditions in the future.