Q.(a) Give an account of allosomal abnormalities in human beings. OR

(a) Klinefelter (XXY), Turner (X0) and XYY syndromes are the classic human sex-chromosome disorders. (b) Isolated, ecologically empty environments let both Darwin's finches and Australian marsupials radiate into many specialised forms from one ancestor.

(a) Klinefelter syndrome arises from the genotype 47,XXY -- an extra X chromosome in a male -- causing tall stature, some development of breast tissue (gynaecomastia), and reduced fertility due to underdeveloped testes. Turner syndrome results from monosomy of the X chromosome (45,X or X0) in a female, causing short stature, a webbed neck, underdeveloped ovaries and typical infertility. XYY syndrome (sometimes called 'super male syndrome') gives males an extra Y chromosome, generally associated with taller-than-average stature and usually only mild or no significant physical/developmental effects. All three arise from errors (non-disjunction) during meiosis affecting the sex chromosomes specifically, which is why they are classed as allosomal, rather than autosomal, abnormalities. (b) Adaptive radiation is the rapid diversification of a single ancestral species into many descendant species, each adapted to a different ecological niche, typically following colonisation of a new, relatively competitor-free environment. Darwin's finches descended from a single ancestral finch species that reached the isolated Galapagos Islands and, in the absence of competing bird species, diversified into more than a dozen species distinguished mainly by beak shape and size, each suited to a different food source (seeds, insects, cactus flowers). Similarly, Australian marsupials, isolated on the Australian continent after it separated from other landmasses ( …