Turner’s syndrome:
The origin of Turner syndrome in an individual is a monosomy in X chromosome. The genotype of the person would be XO. This occurs due to a meiotic non-disjunction.
Down syndrome:
The origin of Down syndrome is a trisomy in chromosome 21. The person has three copies of the chromosome 21 instead of only two. This is due to meiotic non-disjunction or a Robertsonian translocation.
Williams’s syndrome:
The origin of Williams’s syndrome is the result of a deletion. The region of 7q.11.23 in chromosome 7 is deleted in these individuals.
Cri du chat syndrome:
The origin of cri du chat syndrome is also due to a deletion. The bands of 5p15.2 and 5p15.3 in the shorter arm of the chromosome, 5 are deleted.
Syndrome:
A syndrome is the word used when many complex phenotypic changes occur in a person along with a chromosomal aberration. All the four syndromes mentioned above have some symptoms in common. They are:
• Mental retardation.
• Unique body features.
• Unique facial features.
• Low fatality rates.