Final answer:
Among the options given, 'Diploid' refers to the normal state of having two complete sets of chromosomes and is not a condition resulting from an abnormal number of chromosomes; it is the correct option and the exception listed. Therefore, the correct option is D. Diploid.
Step-by-step explanation:
When discussing conditions involving abnormal numbers of chromosomes, it is important to understand certain key terms and concepts. Aneuploidy refers to the presence of an abnormal number of chromosomes in a cell, which includes specific conditions such as monosomy and trisomy. Monosomy is the absence of one chromosome from the normal diploid number, while trisomy is the presence of an extra chromosome. One well-known example of trisomy is Down syndrome, also known as trisomy 21, caused by having three copies of chromosome 21. This condition can lead to intellectual and developmental challenges as well as distinct physical features.
Nondisjunction is a process during meiosis where chromosomes fail to separate properly, leading to gametes with an incorrect number of chromosomes, which may further result in conditions like Down syndrome. Therefore, nondisjunction is directly linked to such chromosomal disorders. However, the term diploid refers to a cell that contains two complete sets of chromosomes, one from each parent, which is the normal state for human somatic cells. Diploid is not a condition that results from an abnormal number of chromosomes but rather the standard chromosomal complement. Therefore, among the options provided, "Diploid" is the exception and does not represent a condition of abnormal chromosome number. This makes it the correct option to the question posed.