Final answer:
A chromosome lacking certain genes has most likely experienced a deletion, where a DNA segment is lost, causing many genes to be missing, potentially leading to lethal genetic imbalances in diploid organisms.
Step-by-step explanation:
If a chromosome lacks certain genes, what has most likely occurred is a deletion. A deletion in a chromosome means that a segment of DNA has been lost, resulting in many genes missing from the chromosome. This genetic change can lead to a genetic imbalance that could be lethal to a diploid organism. It is different from other chromosomal abnormalities such as nondisjunction, which leads to aneuploid gametes; invertions, which can cause chromosomal breaks in the gene; and translocations, which have effects that depend on how the positions of genes are altered.