Identifying the Mismatch in Genetic Conditions

The question asks us to identify the incorrect pairing between a genetic condition and its description from the given options. Let's analyze each statement:

Statement 1: Down's Syndrome - Autosomal trisomy of 21st chromosome

Analysis: This statement is correct. Down's syndrome, also known as Trisomy 21, is a genetic disorder caused by the presence of all or part of a third copy of chromosome 21. It is an autosomal condition because chromosome 21 is not a sex chromosome.

Statement 2: Haemophilia - Sex Linked

Analysis: This statement is correct. Haemophilia is a group of inherited bleeding disorders that results from specific deficiencies in blood clotting factors. The most common types, Haemophilia A and B, are inherited in an X-linked recessive pattern, meaning the gene responsible is located on the X chromosome. This makes it a sex-linked condition.

Statement 3: Klinefelter Syndrome - XO Complement

Analysis: This statement is incorrect and therefore represents a mismatch. Klinefelter syndrome is a genetic condition that affects males. It occurs when a boy is born with an extra X chromosome. The most common karyotype is $47,XXY$. The $XO$ complement (having only one X chromosome) is characteristic of Turner Syndrome, which affects females.

Statement 4: Turner Syndrome - Female with retarded growth

Analysis: This statement is correct. Turner syndrome is a chromosomal condition that affects girls and women. It results from a missing or partially missing X chromosome. The typical karyotype is $45,X$ (also written as $XO$). Common features can include short stature (retarded growth) and developmental issues.

Conclusion on Mismatch

Based on the analysis, statement (3) incorrectly pairs Klinefelter Syndrome with the $XO$ complement. Klinefelter syndrome is typically associated with an $XXY$ karyotype, not $XO$. The $XO$ complement is associated with Turner Syndrome.