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Human sex identification in forensic science

Sex identification has to be determined in cases of – heirship, marriage, divorce, legitimacy, impotence, rape, etc.

A normal person has 46 chromosomes. The chromatin pattern in male is XY and in female XX. Masculine and feminine characteristics most directly depend on the level of circulating sex hormones.

SEX CHROMATIN

It is a small planoconvex mass, (about one micron in diameter) lying near nuclear membrane (Barr body, demonstrated by Dixon and Tarr). In the buccal smear, the percentage of nuclei containing chromatin body ranges from zero to four in males and 20 to 80 in females.

In females, neutrophil leucocytes contain a small nuclear attachment of drumstick form (Davidson body) in up to six percent of cells. This is absent in males. In decomposed bodies sex chromatin cannot be made out.

Sex identification
Sex identification

Exact sex identification can be made using a single specimen of buccal smear, saliva or hair follicle, by the combined treatment of quinacrine dihydrochloride staining for Y chromosome which is seen as bright fluorescent body in the nuclei of male cells, and fluorescent Feulgen reaction using acriflavin Schiff reagent for X chromosomes, which is seen as bright yellow spot in the nuclei.

The percentage of quinacrine positive bodies ranges from 45 to 80% in males, and 0 to 4% in females. With Feulgen reaction technique, fluorescent bodies are found in 50 to 70% of cells in females, and 0 to 2% in males.

By using fluorescent dyes Y chromosome can be demonstrated in dental pulp tissue up to one year. F-bodies are seen in 30 to 70% of cells in males and 0 to 4% in females.

Sex identification from dental pulp, bone marrow and amniotic fluid. Karyotyping (study of chromosomal constitution of the nucleus of a cell for sex identification) of foetus may be done from lymphocytes, amniocytes and fibroblasts.

In normal cases, sex identification is easy from external examination only, but it is difficult in cases of hermaphroditism, concealed sex, advanced decomposition, and skeleton.

INTERSEX

It is an intermingling in one individual of characters of both sexes in varying degrees, including physical form, reproductive organs and sexual behaviour. It results from some defect in the embryonic development. It can be divided into four groups.

Gonadal Agenesis

In this condition, the testes or ovaries have never developed. The nuclear sex is negative.

Gonadal Dysgenesis

In this condition, the external sexual structures are present, but at puberty the testes or the ovaries fail to develop.

(A) Klinefelters Syndrome

In this condition, the anatomical structure is male, but the nuclear sexing is female. The sex chromosome pattern is XXV (47 chromosomes). It is usually diagnosed when there is a delay in onset of puberty, behavioural disorders and mental retardation.

Axillary and pubic hair are absent, and hair on chest and chin are reduced. Gynaecomastia, azoospermia, low levels of testosterone, sterility, increased urinary gonadotrophins, signs of eunachoidism and increased height are common. Testicular atrophy with hyalinisation of seminiferous tubules is seen histologically.

(B) Turner’s syndrome

In this condition, the anatomical structure is female, but the nuclear sexing is male. It can be recognised at birth by oedema of the dorsum of the hands and feet, loose skin folds in the nape of the neck, low birth weight and short stature.

It is characterised by primary amenorrhoea, sterility, lack of development of primary and secondary sexual characteristics, increased urinary gonadotrophin excretion, pigmented naevi, a short fourth metatarsal, webbed-neck, shield-chest, wide-set nipples, high-arched palate, low-set ears, slow growth, learning problems, spina bifida, coarctation of aorta, septal defects, renal defects, Cushing’s syndrome and a high incidence of diabetes mellitus. The ovaries do not contain primordial follicles (ovarian dysgenesis). The sex chromosome pattern is XO (45 chromosomes).

True Hermaphroditism

This is a very rare condition of bisexuality in which an ovary and a testicle or two ovotestis are present with the external genitalia of both sexes. The gonad may be abdominal, inguinal or labio-scrotal in position. There may be uterus. Phallus may be penile or clitoral; the labia may be bifid as in female or fused resembling the scrotum of the male. Neither gonad is completely functional. The somatic sex chromatin may be male or female.

Pseudo-hermaphroditism

In this condition gonadal tissue of only one sex is seen internally, but external appearance is of the opposite sex. (A) Male pseudohermaphroditism: Nuclear sex is XY, but sex organs and sexual characteristics deviate to female form, because of testicular feminisation. (B) Female pseudohermaphroditism: Nuclear sex is XX, but deviation of sex organs and sexual characters towards male are seen, due to adrenal hyperplasia.

Concealed Sex Criminals may conceal their sex to avoid detection by changing dress or by other methods. This can be detected by physical examination.

In advanced putrefaction, Sex identification can be done by identifying uterus or prostate which resist putrefaction for a long time.

SKELETON

Human skeleton is both exo-and endoskeleton. Recognisable sex differences do not appear until after puberty except in the pelvis, and the accuracy from this bone is about 75 to 80% and without pelvis only 50%. Sex identification is rarely based on any one skeletal feature alone. The sex identification is based mainly upon the appearances of the pelvis, skull, sternum and the long bones.

In the skull, sexual features are modified by senility. In the pelvis, sex features are independent of each other and one may even contradict the other in the same pelvis. The male pelvis stands higher and more erect than the female pelvis. Perforated olecranon fossa is more common in females on the left side. Additional information may be obtained from the scapula and metacarpal bones.

In females, subpubic angle, greater sciatic notch, pelvic inlet and outlet are more than in male, but obturator foramen is smaller and curve of ilium is less. The sternal index, ischiopubic index and sciatic notch index are more in females. Greater sciatic notch is the ideal feature to determine the sex of a female child.

Medullary Index of bones : The sex of the long bones can be determined on the basis of their medullary index (Diameter of medulla÷diameter of whole bone x 100) from tibia, humerus, ulna and radius.

According to Krogman, the degree of accuracy in sexing adult skeletal remains is: Entire skeleton 100%, Pelvis alone 95%, Skull alone 90%, Pelvis plus skull 98%, Long bones alone 80%.

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