Numerical chromosomal aberrations can be due to abnormalities in autosomes as well as sex chromosomes. Elaborate in terms of the effects these have on human body, giving suitable examples. (Answer in 250 words)

- Numerical chromosomal aberrations can be due to abnormalities in autosomes as well as sex chromosomes. Elaborate in terms of the effects these have on human body, giving suitable examples. (Answer in 250 words)
Introduction
Numerical aberrations are departures from the diploid 46 chromosomes, arising mainly from non-disjunction. Their effects differ sharply according to whether the extra or missing chromosome is an autosome or a sex chromosome.
Body
1. How they arise: failure of homologues to separate at meiosis I, or of sister chromatids at meiosis II, produces disomic gametes and hence trisomy or monosomy. Anaphase lag loses a chromosome and, occurring after fertilisation, yields mosaics. Dispermy or failure of cytokinesis produces triploidy. The maternal age effect follows from decades of oocyte arrest and cohesin loss.
2. Autosomal aberrations: trisomy 21, at roughly one in 700 births, gives Down syndrome, with hypotonia, epicanthic folds, a single palmar crease, congenital heart defects, intellectual disability and early Alzheimer changes; about 4 per cent arise from a Robertsonian translocation, which carries recurrence risk. Trisomy 18 (Edwards) brings clenched hands, rocker-bottom feet and death in infancy; trisomy 13 (Patau) brings holoprosencephaly, cleft lip and polydactyly. Autosomal monosomy is not compatible with life.
3. Sex chromosomal aberrations: 47,XXY, Klinefelter syndrome, about one in 600 males, gives tall stature with long limbs, small firm testes, gynaecomastia, azoospermia and mild verbal deficit. 45,X, Turner syndrome, gives short stature, webbed neck, cubitus valgus, streak gonads, primary amenorrhoea and aortic coarctation, with normal intelligence, though the great majority of such conceptuses abort. 47,XXX and 47,XYY are largely unremarkable and often undiagnosed.
4. Why the two classes differ: X-inactivation and the gene-poor Y buffer sex-chromosome imbalance, whereas autosomal trisomy imposes full dosage excess on hundreds of genes.
Conclusion
Only the smallest, gene-poorest autosomes are survivable in trisomy. Sex chromosome anomalies are commoner precisely because dosage compensation makes them tolerable.