Final answer:
Genetic disorders in humans are primarily caused by genetic mutations and inheritance factors including chromosomal abnormalities. Conditions such as cystic fibrosis and Down syndrome are examples of disorders that result from these causes. The correct option is a.
Step-by-step explanation:
Two major causes of genetic disorders in humans are A) Genetic mutations and environmental factors. Genetic mutations include alterations in the DNA sequence of a gene, leading to a change in the gene product, which can cause disorders like cystic fibrosis. Environmental factors, which often interact with genetic predispositions, can include various external conditions that may contribute to the development of genetic disorders.
Inheritance is also a crucial factor as many genetic disorders are inherited from one's parents. This can occur in various patterns including autosomal dominance and recessiveness, X-linked dominance and recessiveness, and others. Abnormal numbers of chromosomes, such as an extra copy of chromosome 21 in Down syndrome, are also a cause of genetic disorders.