Age, Sex and Population Variation as Genetic Marker | Anthropology Optional for UPSC PDF Download

Introduction

In the chapter on Races and Racial Classification we have observed that human populations vary in morphological and genetic characteristics. Apart from this, it has been observed that huma populations also vary greatly in physiological characteristics like haemoglobin level, fat level, blood pressure and sense perception. This variation in physiology is not only seen between different populations, but also among the members of the same population. These physiological characters vary, so much that they are different in same person during different period of time. In short, the physiological aspects in man vary depending on age, sex and population.

Variation in Haemoglobin Level

• The Red Blood Corpuscles (RBC) of blood carries Haemoglobin. Haemoglobin has a complex molecular structure. It is made of a heme group which contains iron and four protein chains.
• Metabolic Limit of RBC The haemoglobin level in a cell fluid is approximately 35 grams per decilitre (gm/dl),. The level of Haemoglobin (Hb) never rises above this level is called the metabolic limit of RBC. Maximum concentration is seen in RBC.
• In 1977, Owen has studied the variation in Hb level according to Age. He, along with Pearson studied Quebec society in Canada and has indicated that from the age of 20 years to 60 years the level of Hb among the males is maintained at 15.3 gm/dl. The females reach the highest level of Hb, which is 13.5 gm/dl by the age of 10 -14. After the age of 14. the boys improve their Hb level by attaining 15.3 gm/dl whereas females more or less remain stagnant. 
• This difference of 2 gm/dl between males and females can be attributed to the menstrual losses among the females. Moreover, there is lesser number of RBCs in a female. For this reason, Allan and Girdwood in 1982 have indicated that an Hb level of 12 gm/dl among males is considered to be a situation of Anemia whereas it is a normal situation among females.
• There is a growing interest in ethnographical diversities in Hb level in different populations. It has been observed that there is a relative influence on Hb level by the activity level of the population. Those cultures which demand higher activity from their peoples have selective pressure on Higher level of Hb.. At the same time culture and socio-economic statuses also influence Hb level. Since the nutritional levels of people are more often than not cultural adaptations they significantly Influence the Hb level among the people in a population. In most of the ethnic groups, it has been found that there is a gradual increase in Hb level till age of 30.
  Among the Americans, a constant value is maintained throughout the life and it  graduaIly starts falling only in the old age.
• Recent studies conducted in this context indicate that there is a growing secular trend in Hb level. The rise in Hb level in primitive societies is greater than the level prevalent in advanced societies  several years ago. This trend is similar in all the ethnic groups.

Glucose 6 Phosphate Dehydrogenase-G6PD

• There are some populations and individuals who show a deficiency of G6PD, which is an enzyme. G6PD deficiency is a heritable disorder. People with this deficiency exhibit a response in their blood called haemolytic response to some drugs and food items like fava or broad beans which are common foods in the Middle East. If an individual with this (deficiency consumes these food items, it may result in a condition called haemolytic anaemia or Favaism. The deficiency of this enzyme results in a condition where the subjects-erythrocytes or red-blood cells show low levels of reduced glutathione.
• Glutathione Stability Assay or test is use of to detect people with this problem. GSPD deficiency is an X-linked disorder and is caused by a single gene. Middle Eastern populations exhibit this condition with over 60% of incidence reported among the Kurdish Jews. In Africa, especially the equatorial region, the frequency of this problem is around 10-20% and the trait is also common in some parts of Greece and Iran. Thailand and Micronesiam populations also exhibit this trait with incidence rates of around 10%. 

Transferrins

• Transferrins are beta globulin factors present in the serum of blood and they are capable of binding the ferric ions in the blood tissue. They are also called Siderophilins. Normal individuals exhibit the presence of only one transferring band denoted by TfC. However, amongst some other groups, especially the Australian Aborigines, there Is an extra band of transferring TfD.
• Transferrin is determined by a single gene. A third variant of transferring is also reported amongst some East Asian populations and Lapps and this variant is represented as Dem. Usually, transferrin polymorphism is determined by many alleles at a single locus in an individual's genome.

Haptoglobins

• There are two globulins that are capable of biding free haemoglobin that has escaped from the RBCs. This binding is crucial as it prevents haemoglobin from damaging the kidneys by passing through glomeruli. The haptoglobins are found in the blood serum and can be separated by electrophoresis. In 1955, Smithies recognized that the patterns of haptoglobins are not same in all individuals and there are three types Type 1-1, 2-2 and 2-1.
• Family studies' have indicated that*the above patterns are inherited and possibly more than one allele is involved. These alleles (recognized later to be two) are named Hpy1  and Hpy2. Population studies indicate that the frequency of Hpy1 gene is around40% in Western Europe, its incidence is much higher in tropical Africa. It has lower "values In South Africa (30%). In Asia, its frequency is much lower about 10%. The selective forces at work are not clearly known. In some infections and inflammatory diseases, higher levels of haptoglobins are found.

Variation in Body Fat

• There is a unique distribution of fat, especially subcutaneous fat over the body. Heredity and environment have a significant role to play in establishing the fat level of the person.
• Subcutaneous fat layer has age related changes. Fat begins to be laid in the fetus at about 34 weeks and increases from then on until birth and until nine months after the birth.
• When the child is attaining prepubescent height i.e., from 9 months to 8 years, the fat level shows negative velocity. This decrease in the fat level is due to the breakdown of fat by the growth hormone. This fact is also supported in cases where a deficiency of growth hormone brings about an increase in fat level.
• The fat content present, around bones and muscles decrease with increase in their size. The fat level of the body also shows sex related variations. While both boys and girls show reduction in fat level till the age of 8 years, the decrease in girls is comparatively slow.
• An increase, in-the fat level of the body marks the period from g years to puberty, in both the sexes. It is only at adolescence that a temporary halt in increasing fat level is seen among the boys and this joss of fat is gained back after 20 years. This temporary  halting among the boys is seen in trunk and limbs while there is no such loss among, the girls.
• The nutrition level and the level of activity are other facts with a socio economic dimension which control fat level, Increased nutrition and decrease in activity level increases the fat level of the body. This is the reason why in industrial societies fat related disorders are very common. Genetics also control the fat level deposition to an extent. In some ethnic groups, there is an increased deposition of fat in thighs and buttocks, a condition called steatopygia which occurs in Busmen and Hottentots populations.

Pulse Rate

• Pulse is the number of heart beats per minute. The pulse is measured at the wrist, neck, temple, groin, behind the knees, or on top of the foot. In these areas, an artery passes close to the skin. Measuring the pulse can give very important information about the health of a person. 
• Any deviation from normal heart rate can indicate a medical condition. Fast pulse may signal the presence of an infection or dehydration. In emergency situations, the pulse rate can help determine if the patient's heat is pumpimg.
• The pulse measurement has other uses as well. During exercise or immediately after exercise, the pulse rate can give information about the fitness level and the health of a person. Pulse rate varies according to the age of persons, whether they exercise or not and other physiological conditions in the body.

For resting heart rate

• Newborn infants; 100 to 160 beats per minute
• Children 1 to 10 years; 70 to 120 beats per minute
• Children over 10 and adults; 60 to 100 beats per minute
• Well-trained athletes; 40 to 60 beats per minute

Resting heart rates that are consistently high (tachycardia] and resting heart rates that are below the normal values (bradycardia) may indicate a problem.
Changes in the oxygen pressure, high altitude areas and other metabolic demands on the body may also cause change in the pulse rates.

Variation in Blood Pressure

• The blood pumped by heart into blood vessels for its distribution to different parts of the body must leave the heart at some pressure because it has to overcome the resistance offered by frictional and other forces, The pressure at which blood leaves heart is called systolic blood pressure (SBP) and it gives an estimate of contractility of the heart. As heart expands or relaxes, these pressure drops, which give a measure of diastolic blood pressure (DBP). It is at this pressure that heart receives blood.
• A rise in the SBP indicate increased contraction whereas a rise in the DBP indicates decreased relaxation of the Heart, both being, harmful if they cross optimum levels. Blood-pressure is indicated in fraction the upper number indicating SBP and the lower number indicating DBP. Though a pressure of 120/80 is considered an average for the adults, values as low as 115/70 is also considered normal. For the SBP, 100 plus age is. also considered normal. Researches show positive correlation between blood-pressure and age, sex, heredity, body composition, and social status.
• Knowledge about blood-pressure at the population level is of utmost importance in the assessment of health status, particularly in the detection of cardiovascular diseases. The variations in blood pressure according to age is high during growth and deveIopment up to adolescence, thereafter it shows a rhythmic variation on a daily basis.
• The blood pressure in the neonates during first day averages 70/50. There occurs increase in blood pressure during the next several months to approximately 90/60.. The rate of increase is higher during this period. Thereafter, it remains more or less same throughout the adult period.
• Using family studies, it has been possible to underline factors for blood pressure variation in a population. It has been, estimated that 16% of blood pressure variation is due to environmental factors, 48 percent of. additive genetic factors, and 36 percent to dominance. Heredity is indicated in causation of blood pressure because it has been shown to run in families though environment seems to be the precipitating agent.
• According to Kaplan (1978), the populations can be arranged into three groups on the basis of variation of the blood pressure.
  (a) Hypertensive
  Systolic blood pressure > 169 mm Hg
  Diastolic blood pressure > 95 mm Hg
  (b) Borderline cases
  S.B.P. 140 - 160 mm Hg
  D.B.P. 90 - 95 mm Hg
  (c) Normotensives
  S.B.P. < 140 mm Hg
  D.B.P. < 90 mm Hg
• In a majority of rural Indian population the percentages of the normotensives have been almost always found to be more than 95%. In many cases, percentage of normotensives and hypertensives has been found to be higher than borderline. This indicates that in majority of the populations, persons either are normotensives or hypertensives. The cardiovascular system perhaps has the ability because of homeostatic mechanisms, to sustain changes due to stress and strain of environment. This seems to have a threshold limit. Once it is crossed, there is no scope of return and a normotensive becomes hypertensive. This may be reason for low percentage of borderlines compared to hypertensive patients.
• On the contrary, studies conducted indicate that in industrialised population the proportion of normotensives in comparison to hypertensives is not so high. Hpyertensives are around 5% subjects showing increase in both SBP and DBP. Another feature of the industrialised society is a small but significant group of borderlines. This is probably because the homeostatic mechanisms are disturbed in such societies due to nutritional and life style reasons. Among the nutritional reasons, absence of green vegetables and fruits and inclusion of fat to a great extent in the diet have been the most glaring reasons for the increase in percentage of border-line cases and hypertensive.
• In cases of both rural and urban populations, it has been found that the Variations of the blood pressure tend to be lower in the household samples than that of hospital. It is probably due to natural settings of the house/free from anxiety and tension. Blood pressure, as it is a multifactoral condition, may tend to recover in situations of normal, tension-free emotions. Scientists associated with such population studies of blood pressure variation outside India are Boyce Attenborough, Harrison - Thornabrook and Sinneff. The group has been involved in recording population variation in blood pressure since 1970. They have analysed populations of New Guinea etc. and have reached to the same conclusions that in addition to heredity, diet and stress and strain of life are the two most important causative environmental factors of high blood-pressure.

Variation in Sense Perception

• There have been sortie population studies of physiological variations that include survey of different sensory mechanisms. Among the various sensory mechanisms, the most thoroughly surveyed are ability to taste phenylthiocarbamide and red and green colour blindness. The ability to taste PTC is an autosomal polymorphic trait (Vogel and Motulsky) Tasters with genotypes TT, Tt have the ability to taste the substance while non tasters are homozygous for the recessive allele 't'.
• The defective colour vision has long been used as a genetic marker in the study of human variation. Red-green colour blindness is an X-linked trait in which individuals fail to distinguish red and green from other colours. Various populations inside and outside our country have been surveyed like Turkey, Balkans Nigeria, Myanmar, etc. In India, such studies have mainly been conducted in South India.
• Most of the studies related to PTC tasting have found sex-differences in the trait: females are found to be more sensitive to the taste of PTC than males and the difference is statistically significant. Balkan, Burmese-and Nigerian population. Though females are more sensitive than males, the difference does not appear to be significant one. Muslims of India also do not show sex differences in ability to PTC tasting.