Question

This abnormality occurs due to monosomy (2n-1) ; the individual has 2n=45 chromosomes with 44 + XO genotype
A. Edward's syndrome
B. Down's syndrome
C. Turner's syndrome
D. Klinefelter's syndrome

Answer 1

This abnormality causes the females sterility, their ovaries are poorly developed, their small uterus and their breasts are underdeveloped. Their neck becomes webbed and their chest becomes broad.

Complete answer:
Let's start with option A which is Edwards's syndrome. It is also called Trisomy 18 and this disorder is a genetic disorder which causes developmental delays because there is presence of an extra 18th chromosome. This syndrome is rare but it is a serious condition. Since this syndrome is due to the extra 18th chromosome, it is an incorrect option as in the question that syndrome is asked which is due to monosomy. Therefore, this option gets eliminated.
Moving to option B which is Down's syndrome. This syndrome is known as Trisomy 21 and this is a genetic disorder which is caused when there is division of abnormal cell which further results in extra genetic material as there is presence of an extra chromosome 21.Therefore, this option is incorrect as this is caused by presence of extra chromosome 21st not due to monosomy. So, it gets eliminated.
Moving to option C which is Turner's syndrome. This syndrome is the most common type of genetic disorder in females. This is caused by monosomy (2n-1) which means that either X chromosomes are missing or X chromosomes are altered. In normal females there is a presence of 44+XX chromosomes but due to this disease, they have 45 chromosomes i.e., 44+XO instead of having 46 chromosomes. So, this option is the correct one as it occurs due to monosomy (2n-1) ; the individual has 2n =45 chromosomes with 44 + XO genotype.
Last option is D which is Klinefelter's syndrome. It is a sex chromosome disorder in boys and men where there is presence of an extra X chromosome and the karyotype is 47, XXY. In normal males, sex chromosome is XY but in diseased one, they have XXY since there is presence of extra one or more X chromosome. Therefore, it is not due to monosomy and it is the incorrect option.

Thus, the correct option is C which is Turner's syndrome.

Note: The individual which has 2n=45 chromosomes with 44 + XO genotype instead of 46, they have turner's syndrome as this syndrome is caused due to the absence of X chromosome in females and make these females sterile. Generally each female has two X chromosomes but this syndrome results when there is only one X chromosome present in their cells.