Which syndrome is characterized by an individual having an extra X chromosome?

Klinefelter's Syndrome is a genetic condition that occurs in males who have an extra X chromosome, resulting in a total of 47 chromosomes instead of the typical 46. The presence of this additional X chromosome affects physical and cognitive development, leading to characteristics such as reduced testosterone levels, infertility, and sometimes breast development. Males with Klinefelter's Syndrome may also experience learning difficulties and delayed speech and language development.

The other conditions listed involve different genetic anomalies. Turner Syndrome is associated with females who typically have only one X chromosome, which leads to various developmental issues. Down's Syndrome results from an extra copy of chromosome 21, not an additional X chromosome. Sickle Cell Anemia is a blood disorder caused by a mutation in the hemoglobin gene, unrelated to chromosomal abnormalities. Each of these conditions has its unique genetic basis, highlighting the specific nature of Klinefelter's Syndrome linked to the presence of an extra X chromosome.