Study Group. We studied 100 LC patients, 50 pulmonary TB patients and 50 healthy non sibling controls matched in sex, age and smoking habits. All diagnoses were established at the Clinical Centre of Serbia Institute of Lung Diseases and Tuberculosis in Belgrade, Serbia. Diagnosis of LC was based on histological examination of the tissue obtained dur­ing bronchoscopy, by fine needle aspiration biopsy or open lung biopsy. Pulmonary TB was confirmed by positive results of sputum culture on Lowen-stein-Jenssen medium and/or by histology. Control group consisted of spouses/partners of patients or employees of the Institute of Lung Diseases and Tuberculosis in Belgrade, Serbia, with 20 or more years exposure at the working place, who had not developed TB or LC by the time of the study.

Methods. Establishing genetic homozygosity in humans is a very delicate assignment, because we know only a small number of loci with allelogenes that determine an exact biochemical process [25]. Knowing the type of inheritance and variability we can see that series of morpho-physiological traits are under control of one small number of genes. Some homozygously-recessive traits of the head and neck region are: straight, soft hair and blond hair (OMIM numbers 139450 and 210750), inability to roll, fold and curve the tongue (OMIM number 189300), in-sensitivity to PTC (gene location 7q35-q36, OMIM number 607751), color blindness (gene location Xq28, OMIM number 303800), while the others are clearly expressed in human arms and legs like hand clasping pattern, left handedness (gene location 2p12-q22, OMIM number 139900), distal or proxi­mal hyper-extensibility of the thumb, index finger shorter than the ring finger (OMIM number 136100), and so on [23]. Some of the traits are still a matter of intensive research such as blue eyes, previously found gene location 19p13.1-q13.11 (OMIM num­ber 227240) and newly discovered at the 15q13.1 as the predominant region involved in human iris color [26]. Using this information, several authors of Bel­grade population-genetic studies have studied the distribution and frequency of a series of extremely expressed recessive traits to estimate individual and group differences, i.e., comparison between ill and healthy individuals, pupils with special needs, car­riers of different blood types, members of different ethnic groups, etc. [25,27-31].

We examined a total of 23 specific HRCs (list­ed in Table 1), characterized by Marinkovic et al.

[27,28], in each subject from the three groups. The study was approved by the Ethics Committee of the Clinical Centre of Serbia, Belgrade, Serbia, and its purpose was described to all the individuals in the three groups. Ability to recognize the bitter taste of PTC was tested following original instructions of Harris and Kalmus [32] and the color-blindness test was performed according to Ishihara [33].

Statistics. We used a combination of x2 test, Turkey's test, non parametric variance analysis, two-by-two x2 tabs, equal proportion test, and Wahlund's variance - the inter-population fixation index (F_st), in a stepwise manner. Recessive allele frequencies (q) were determined according to the formula: q =VR/N (R = number of the individuals with recessive character; N = number of individuals in population). Wahlund's variance (F_st) was determined according to the formula: F = (qi -q')²/q'(1-q') (qi = the frequency of the i-allele in the group; q'= average frequency of the allele).