Final answer:
Tay-Sachs disease and cystic fibrosis are examples of diseases associated with lethal recessive genes, while Huntington's disease is an example of a disease related to a dominant lethal allele. Mutations are at the core of these genetic disorders, affecting the DNA sequence and resulting in fatal conditions.
Step-by-step explanation:
A disease associated with lethal recessive genes is Tay-Sachs disease. This is a fatal genetic disorder that affects the nervous system and leads to death in early childhood, usually before age 5. It occurs when a child inherits two copies of the faulty allele, one from each carrier parent. Another example of a recessive genetic disorder is cystic fibrosis, which causes thick mucus in the lungs and can severely affect respiration.
On the other hand, Huntington's disease is associated with a dominant lethal allele. This means that individuals who inherit just one copy of the defective gene from a parent will develop the disease, which causes nerve cell degeneration and is invariably fatal. However, symptoms typically don't appear until middle age, after individuals may have already had children, allowing the allele to be passed on.
Mutations play a significant role in both types of genetic disorders. These changes in the DNA sequence can arise spontaneously or due to environmental factors, and they can lead to diseases with various modes of inheritance, including dominant lethal and recessive lethal patterns.