Question

name a disorder give its karyotype and write the symptoms a human suffers do to monosmy of sex chromosomes

Answer 1

Disorders of the sex chromosome (like disorders of the autosomes) can be either numerical or structural, and can be present in all cells or in a mosaic form. Clinical indications that should raise suspicions of a sex chromosome abnormality are:

delay in onset of puberty;

primary or secondary amenorrhea;

infertility;

ambiguous genitalia.

These disorders are considered very common with incidence of about 1:400–500. Phenotypes associated with sex chromosome disorders are less severe than autosomal defects and this is mainly due to X chromosome inactivation, as well as the fact that Y chromosomes have a low gene content. X chromosome inactivation is the the process by which most genes on one of the two X chromosomes in females are silenced epigenetically and randomly, and so fail to produce any product. In somatic cells in normal females (but not in normal males), one X chromosome is inactivated early in development, thus equalizing the expression of X-linked genes in the 2 sexes. Thus females are mosaic with respect to X-linked gene expression.

Males normally have a chromosomal makeup of XY, but an affected individual with Klinefelter syndrome will have at least two X chromosomes and at least one Y chromosome.

This syndrome is typically characterized by a 45,X karyotype in females (in about 50% of cases), with the absence of one X chromosome (and therefore absence of a Barr body). The single X chromosome is of maternal origin in about 70% of cases; therefore there is loss of a sex chromosome due to paternal error. Other possible variations include:

46,X,i (Xq) in 15% of cases (isochromosome of X);

45,X or 46,XX mosaics in 15% of cases;

45,X or 46,X,i (Xq) mosaics in about 5%;

other.

This syndrome usually results from errors in maternal meiosis I (90% of cases), and its incidence is about 1:1000. Such patients have non-specific features e.g. average intelligence, normal sexual development. About 70% have serious learning problems. In 47,XXX cells, two of the X chromosomes are inactivated. Variations include:

tetrasomy X syndrome (48,XXXX) with more serious physical and mental retardation;

pentasomy (49,XXXXX) with severe developmental retardation.

It has an incidence of about 1:1000 male live births. It may be caused by paternal non-disjunction at meiosis II (producing a YY sperm) or by a post-zygotic event. Variants of this syndrome include XXYY and XXXYY, which probably also originate from paternal non-disjunction at both meiosis I and II. Patients are usually phenotypically normal and may have the following features:

tall stature;

severe acne;

average intelligence;

antisocial behavior with increased risk of behavioral problems (3% are in prisons & mental hospitals);

can show emotional immaturity and impulsive behavior;

normal fertility, without risk of chromosomal aberrations in offspring;

normal sexual development.

Answer 2

Turner syndrome

karyotype= X0

SYMPTOM

1) STERILE FEMALE WITH RUDIMENTARY OVARY

2)LACK OF SECONDARY SEXUAL CHARACTER

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