Final answer:
A loss of certain genes in a chromosome typically indicates a deletion, a type of chromosomal abnormality where a DNA segment is missing, which can be lethal to a diploid organism.
Step-by-step explanation:
If a chromosome lacks certain genes, what has most likely occurred is 5) a deletion. Deletion refers to the loss of a segment of DNA from a chromosome, which results in the absence of those genetic segments and is often lethal to a diploid organism. This genetic abnormality can have significant effects depending on which and how many genes are lost. Other chromosomal abnormalities include nondisjunction, which leads to the creation of gametes with an abnormal number of chromosomes, while translocations and inversions involve rearrangements of segments of chromosomes that can lead to breaks in genes or altered positions of genes, respectively. However, deletions are specifically associated with the absence of genetic material.