Final answer:
Fragile X syndrome is a genetic disorder caused by a mutation on the X chromosome. It is classified as a chromosomal disorder, not as an autosomal or mitochondrial disorder, and it is not the same as Down syndrome, which is caused by having an extra copy of chromosome 21, known as trisomy 21.
Step-by-step explanation:
What is Fragile X Syndrome?
Fragile X syndrome is a genetic disorder that results from a mutation in a single gene on the X chromosome. It is neither an autosomal disorder, like Down syndrome, which involves an extra copy of chromosome 21, nor a mitochondrial disorder since it specifically affects the X chromosome. Chromosomal disorders like Fragile X syndrome involve changes in the number or structure of chromosomes. For example, Down syndrome is caused by trisomy 21, where three copies of chromosome 21 are present due to nondisjunction during meiosis.
Genetic disorders caused by abnormal numbers of chromosomes often involve the X chromosome because males (having only one X chromosome) are more likely to express recessive traits found on it, and because the mechanisms that determine sex-linked inheritance include specific pathways to handle various X chromosome counts.
Chromosomal Defects
Chromosomal defects typically occur due to errors in cell division, specifically during meiosis, which is when reproductive cells are formed. When nondisjunction occurs, it results in gametes that either have too many or too few chromosomes. Embryos with extra chromosomes often do not survive to birth; however, some conditions, such as Down syndrome, can result in live births.