Final answer:
The type of chromosome breakage that results in small deletions undetectable on a karyotype is known as a microdeletion, which can be identified through more detailed genetic testing methods.
Step-by-step explanation:
The type of chromosome breakage that results in very small deletions that are too small to identify on a karyotype is known as a microdeletion. A karyotype is a test that examines the number and structure of a person's chromosomes in order to detect genetic abnormalities. While it can reveal certain genetic conditions such as Down syndrome and Turner syndrome, which involve the duplication or loss of entire chromosomes, it may not detect smaller genetic changes like microdeletions. These very small deletions may span only a few genes and are typically uncovered through more detailed genetic tests such as microarray analysis or next-generation sequencing.