4 public questions tagged with this topic.
Cri-du-chat syndrome is caused by a deletion in the short arm of chromosome 5.
Ref: NCERT Class 12 Biology Chapter 4: Principles of Inheritance and Variation Non-Mendelian Inheritance - Incomplete Dominance Co-dominance Multiple Alleles
Deletion removes genetic information, causing loss of coding sequences and regulatory elements, leading to haploinsufficiency or unmasking recessive alleles. No template remains to compensate. Duplication adds an extra copy of a segment; original information is retained, and dosage increase is often better tolerated because essential functions persist. Cells can inactivate, down-regulate, or evolve divergence of duplicate copies, reducing harm. While large duplications still disrupt dosage balance, viability is higher than comparable deletions, explaining prevalence of polymorphic copy-number variants in human genomes.
Ref: Hartl & Ruvolo, Genetics, 6th ed., Chapter 12: Deletion vs Duplication Consequences
Cri-du-chat syndrome, or 5p- syndrome, results from terminal deletion of the short arm of chromosome 5. The critical interval at 5p15.2 contains dosage-sensitive genes like CTNND2 involved in neuronal migration. Haploinsufficiency causes cat-like cry in infants due to laryngeal hypoplasia, microcephaly, severe intellectual disability, and distinctive facial dysmorphism. Deletion size correlates with severity but minimal critical region defines syndrome. Most cases are de novo deletions; 10-15% arise from parental balanced translocation. Diagnosis relies on karyotype and FISH or microarray demonstration of 5p loss.
Ref: NCBI Bookshelf, Genetics: Cri-du-Chat Syndrome; Nussbaum et al., Thompson & Thompson Genetics in Medicine, 9th ed., Chapter 6
Deletion mapping exploits defined chromosomal deletions removing contiguous segments to locate genes physically relative to breakpoints. Heterozygous deletion crossed to recessive point mutant uncovers mutant phenotype if point mutation lies inside deletion interval because no wild allele remains; if outside wild allele from deletion chromosome restores function. Using overlapping deletions of known breakpoints gene order determined by pattern of uncovering across deletion panel. Technique predated sequencing and provided essential physical map complementing recombination maps and revealing gene proximity and clustering accurately.
Ref: Griffiths et al., Introduction to Genetic Analysis, 12th ed., Chapter 12: Deletion Mapping and Gene Order Determination
