Absence or excess or abnormal arrangement of one or more chromosomes results in

Options

A. Point mutation
B. Chromosomal disorders
C. Mendelian disorders
D. Gene mutation

Answer

### Step-by-Step Solution:

1. **Understanding Chromosomal Disorders**: The question asks about the consequences of the absence, excess, or abnormal arrangement of chromosomes. These conditions are classified as chromosomal disorders.

2. **Definition of Chromosomal Disorders**: Chromosomal disorders arise from abnormalities in chromosome number or structure. This can include conditions like aneuploidy, where there is an abnormal number of chromosomes due to failure of segregation during cell division.

3. **Examples of Chromosomal Disorders**: A well-known example of a chromosomal disorder is Down's syndrome, which is caused by the presence of an extra copy of chromosome 21 (trisomy 21). This occurs when there is a failure of segregation during meiosis, leading to gametes with an abnormal number of chromosomes.

4. **Impact of Chromosomal Disorders**: Individuals with Down's syndrome may experience various developmental issues, including mental retardation and delayed milestones in motor and mental development.

5. **Distinction from Mendelian Disorders**: It is important to differentiate chromosomal disorders from Mendelian disorders, which are caused by mutations in single genes (e.g., hemophilia, sickle cell anemia). Chromosomal disorders involve larger structural changes in chromosomes rather than changes at the gene level.

6. **Conclusion**: Therefore, the absence, excess, or abnormal arrangement of one or more chromosomes results in chromosomal disorders.

### Final Answer:
The absence or excess or abnormal arrangement of one or more chromosomes results in **chromosomal disorders**.

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