Principles Of Inheritance And Variation

Turner's. syndrome (Turner, 1938) or gonadal dysgenesis is due to monosomy (2n-1) � of sex chromosomes. It is formed by the union of an abnormal egg and a normal X sperm or a normal egg and an abnormal sperm. The individual has 2n = 45 chromosomes (44 + X); instead of 46. Such persons are sterile females who have� rudimentary ovaries, undeveloped breasts, small. uterus, puffy. fingers, short stature (less thari 5 feet), webbed neck, abnormal intelligence etc.

Parents in the given condition are with blood groups AB and O .A probable cross between them and the resulting progeny can be represented as follows: So, the father with type 'O' blood and mother with type 'AB' blood could have either A or B blood type children

Down's syndrome is the trisomy of 21 st chromosome (autosomal aneuploidy) in man. Down's syndrome is characterized by short stature, warty skin, protruding tongue, slanting eyes, with folded eyelids (epicanthus folds), short, broad hands with palmer crease, fingers showing characteristic fingerprint patterns. The affected person's face presents a typical mongoloid look. Hence it is also called as mongoloid idiocy. It occurs due to the phenomenon of non-disjunction. Noh-disjunction occurs when a pair of homologous chromosomes does not separate in meiosis but migrate to the same pole of the cell resulting in an uneven number of chromosomes in the daughter cells (47 in one and 45 in other). This numerical abnormality results in trisomy, (2n + 1) and monosomy (2n- 1) respectively. Non-disjunction is more common in sex chromosomes.