Hardy-Weinberg equilibrium study of six morphogenetic characters in a population of Punjab, Pakistan.

Amir Shakeel1, Aneeq-ur-Rehman*1, Junaid Iqbal1, Poonum Rana2

1Department of Plant Breeding and Genetics, University of Agriculture Faisalabad-38040, Pakistan.2Department of Zoology, University of Agriculture Faisalabad-38040, Pakistan.

*For correspondence: aneequrrehman57@gmail.com

Abstract

Hardy-Weinberg equilibrium is the study of the distribution of allelic and genotypic frequency in a population. The objective of this study is to evaluate the allelic and genotypic frequency of different qualitative traits of humans in Punjab, Pakistan. A total of 909 individuals were observed for this study. In population the frequency order of the blood group is B > O > A > AB as well as in male and female. Rh-positive is more (86.0%) than the negative (14.0%) in the population. Tongue rolling ability is more in both males (58.73%) and females (61.5%). The presence of free earlobe is more (71.47%) in the population. Straight hair is more (55.79%) common in the population than the wavy (29.32%) and curly (14.89%). In male and female order is the same as in population. In the population, the nature of hair and dimple are significant but other traits are non-significant. This study concluded that the alleles for the nature of hair and dimple are not in equilibrium in the population. In the male, blood group, nature of hair and dimple while in female blood group, Rh factor and nature of hair are not in equilibrium.

Keywords: Hardy-Weinberg equilibrium, Blood Group, Rh factor, Tongue rolling, Earlobe, Nature of hairs, Dimple.

Introduction

The discovery of Mendel’s law of segregation and independent assortment has led to the foundation of population genetics. In 1908, British mathematician Godfrey H. Hardy and German physician Wilhelm Weinberg independently discovered the relationship between gene and genotype frequencies, known as the Hardy-Weinberg (HW) principle, or HW equilibrium. HW principle has become a powerful research tool in both theoretical and applied research in population and quantitative genetics (Chen, 2010). A population is a set of organisms that belong to the same species, live in a particular environment, effect each other and during crossing give fertile offspring (Jankowska et al., 2011). Population genetics refers to study the distribution of genes or alleles in a population. It also refers to a study the evolutionary changes within and between the ethnic groups (Milgroom, 2015; Grunwald et al., 2017).

HW Principle (Hartl and Clarke, 2007) which formally states that: “If a genetic population is such that (1) organisms are diploid, (2) sexual reproduction, (3) generations do not overlap, (4) mating is random, (5) population size is significantly large, (6) allele frequencies are equal in the sexes, and (7) there is no migration, mutation, or selection, then the genotype frequencies in the population are given by weighted products of the allele frequencies. In the case of the one locus, two allele system have allele frequencies [(A, a) or (p, q)] give directly the genotype frequencies

(AA, aa, Aa) p2+q2+2pq=1. (Bosco et al., 2012). But deviation from the Hardy-Weinberg equilibrium itself strongly suggests that at least one of the assumptions is violated (Chen, 2010).

Blood is the most important fluid for the transport of nutrients, hormones, and oxygen to the whole body (Cavalli-forza and Feldman, 2003). Before 1900, it was thought that all blood was the same. This misconception causes fetal transfusion. After the discovery of ABO blood type in 1901 by Karl Landsteiner and AB blood type in 1902 by Adriano Sturli and Alfred von Decastello, people led to know that human blood is not the same. People have different blood groups, depending upon the surface markers (antigen) found on the membrane of red blood cells (Dean, 2005). Antigen for ABO blood group is a complex carbohydrate (oligosaccharides) and rhesus (Rh) factor is protein in nature (Dean, 2005). ABO blood type is an example of multiple allelism and the allele for A and B is co-dominant over O (Pasha et al., 2009). It was reported that the alleles for ABO blood type are present on chromosome 9 controlling four different phenotypes A, B, AB, and O and Rh factor which is governed by allele D and d present on chromosome number 1 have two phenotypes, positive (with antigen D) and negative (without antigen D). These both ABO blood group and Rh factor have antigenic property on the surface of the membrane of red blood cells (Alimba et al., 2010).

Tongue rolling is the tendency to turn up the lateral edges of the tongue and it is due to the single dominant gene (Liu and Hsu, 1949). Attached or free ear lobe are two possible phenotypes governed by a single gene. A person having homozygous dominant and heterozygous genotype possess free ear lobe while homozygous recessive genotype possesses attached ear lobe (Monheit, 2012). However other factors such as sexual and age effect the length of the earlobes (Azaria et al., 2003).

Hair morphology is a qualitative trait and detectable feature of a human for the study of population genetics. It has three phenotypes, straight, wavy and curliness and composition of hair is keratin protein. Hair has three internal structure cuticle, cortex, and medulla. The investigation showed that there are three types of cells in the cortex region of hair namely orthocortex, mesocortex and paracortex. As the curly nature of hair increase, the mesocortical cells decrease while in straight hairs mesocortical macrofibrils have more in concentration (Thibaut et al., 2007).

Dimples on the cheek can be unilaterally (on one side) or bilaterally (on both sides). It is an indentation of muscles on the cheeks. Dimples are a dominant trait that transfers to the next generation is only due to a single gene (Kosif, 2015). In some people, dimples last only until adolescence, while this trait is a lifetime for some people (Omotoso et al., 2010). In 2009, Starr indicates facial dimples are inherited as autosomal dominant traits and one copy of a dominant gene is sufficient to cause dimples. People having both recessive genes lack the ability to express the dimples on the cheeks (starr, 2009). This study covers Hardy-Weinberg equilibrium in seven morphogenetic characters in the population of Punjab Pakistan.

Materials and Methods:

Total 909 individuals were randomly selected containing male and female in 508 (55.89%) and 401(44.11%) proportion. The study carried out in the University of Agriculture Faisalabad, Punjab, Pakistan. This study used a descriptive research design. The data was collected by morphological observations of different traits shown in table 1.1. The target populations for this study belong to different cities of Punjab in Pakistan as shown in fig. 1.1.

The individuals were randomly selected, total 909 in which males 508 (55.89%) and female 401(44.11%) had age ranged from 4-70 years for the study. We test our results from goodness-of-fit X2 tests at significance 0.05.

Table1.1 Observed characters and traits in individuals.

Sr. No. Character Traits (Phenotypes)1 Blood Group A, B, AB, O2 Rhesus (Rh) factor Positive or Negative3 Tongue rolling Presence (positive) or Absence (negative)4 Earlobe Attach or Free5 Nature of hairs Straight, wavy, Curling6 Dimple Present on both sides, on one side, Absent

1. Blood group: Blood group is controlled by multiple alleles. Allele IA have antigen ‘A’, allele IB have antigen ‘B’ while allele ‘i’ do not have antigen on Red Blood Cells (RBCs). A person with genotype IA IA, IAi have blood group A; IA IB for blood group AB; IB IB, IBi for blood group B and ii for O blood group.

2. Rh factor: Two different alleles for Rh factor know as Rh+ and Rh-. Rh+ individual have Rh antigen on RBCs and Rh- individual does not have.

3. Tongue rolling: The ability to turn up the lateral edges of the tongue is due to the single dominant gene (Liu and Hsu, 1949).

4. Earlobe: Ear lobes may be attached or free in an individual. Attached ear lobe is controlled by a recessive gene while free ear lobe is control by a dominant gene (Ebeye et al., 2014).

5. Hair nature: It is assumed that hair straightness and curliness is control by a single pair of allele showing partial dominance. An individual with straight hair possess homozygous dominant allele (IsIs) and curly hair are governed by a homozygous recessive allele (IcIc). An individual with wavy hair have heterozygous (IsIc) genotype.

6. Dimples: Dimples is depression in the cheeks. It is inherited as an autosomal dominant trait (Ebeye et al., 2014).

Figure, 1.1 Data collected from areas in Punjab, Pakistan

Fig 1.2 Rolling Tongue Fig 1.3 Non-Rolling Tongue Fig 1.4 Attach Earlobe Fig 1.5 Free Earlobe Fig 1.6 Straight Hair

Fig 1.7 Wavy Hair Fig 1.8 Curling Hair Fig 1.9 Dimple present Fig. 1.10 Dimple Absent

Results:

Frequency of blood group ‘B’ (38.01%) is the most commonly present in the population followed by group ‘O’ (27.58 %), group ‘A’ (25.09%), and ‘AB’ group have the least frequency of 9.31%. The ABO percentage frequencies order is B> O> A> AB. The frequency order of both male and female showed a similar result to the whole population. Rh-D positive phenotype has more frequency 86.0% and Rh negative have a low frequency of 14.0% in the population. Rh-D positive phenotype is more in female (87.22%) as compared to male (85.17%). Rh negative is more in male (14.82%) but low in female (12.77%).

The distribution of tongue rolling in population shows 59.96% person has the ability to roll their tongue and 40.04% cannot. It was observed that tongue rolling in female (61.5%) is more as compare to male (58.73%). While 41.26% of males are unable to roll their tongue as compared with females (38.5%). In the population, persons with free earlobe (71.47%) are more as compared to attach (28.53%). Free earlobe (72.99%) is more common in females as compared to males (70.10%).

Straight hair (55.79%) is the most commonly present in the population followed by wavy (29.32%) and least is curly (14.89%). In male and female, straight, wavy and curly hairs are in equal proportion. In population, absence of dimple (75.97%) is more as compared to the presence of dimple (24.03%). Males with dimples are more in number (24.65%) than females (20.82%).

The result showed that ABO blood group, Rh factor, tongue rolling and earlobe are non-significant which mean that the population is in equilibrium in perspective of these traits. But the nature of hair and dimple are significant in the population (Table 1.3) which means that at least one assumption of HW equilibrium is violated.

Tongue rolling and ear lobe showed a non-significant result while nature of hairs and blood group showed a significant result in both sexes. Presence of dimples in male and Rh factor in

female population showed significant results. (Table 1.5) which means that the population is not in equilibrium.

Characters Blood Group Rh factor Tongue Rolling Earlobe Nature of hairs DimpleTraits A B AB O Positive Negative Positive Negative Free Attach Straight Wavy Curly Present Absent

Population% 25.09 38.01 9.32 27.58 86.0 14.0 59.96 40.04 71.47 28.53 55.79 29.32 14.89 24.03 75.97

Male % 26.09 38.41 9.18 26.30 85.17 14.82 58.73 41.26 70.10 29.89 52.88 30.07 17.04 24.65 75.34

Female % 23.05 38.00 9.34 29.59 87.22 12.77 61.5 38.5 72.99 27.00 52.88 30.07 17.04 20.82 79.17

Table 1.2: Data of different traits in a population, in males and females.

Table 1.3: HW equilibrium study of traits in the whole population.Characters Blood Group Rh factor Tongue Rolling Earlobe Nature of hairs Dimple

Traits A B AB O Positive Negative Roller Non-roller Free Attach Straight Wavy Curly Present Absent

Allele p q - r P q p q p q p - q p qAllele

frequency 0.2 0.3 - 0.5 0.6 0.4 0.4 0.6 0.5 0.5 0.7 - 0.3 0.1 0.9

X2 Value X2 =2.89 N.S ,df=3 X2 =2.22 N.S ,df=1 X2 =6.53 N.S, df=1

X2 =5.55 N.S, df=1 X2=77.61*,df=2 X2 =15.17*,df=1

Table 1.4: HW equilibrium study of traits in males.Characters Blood Group Rh factor Tongue Rolling Earlobe Nature of hairs Dimple

Traits A B AB O Positive Negative Roller Non-roller Free Attach straight Wavy Curly Present Absent

Allele p q - r p q p q p q p - q p qAllele

frequency 0.2 0.3 - 0.5 0.6 0.4 0.4 0.6 0.5 0.5 0.7 - 0.3 0.2 0.8

X2 Value X2 =4.18*, df=3 X2 =0.54 N.S, df=1 X2 =6.27 N.S, df=1

X2 =6.34 N.S, df=1 X2=38.93*,df=2 X2 =28.0*, df=1

Table 1.5: HW equilibrium study of traits in females.Characters Blood Group Rh factor Tongue Rolling Earlobe Nature of hairs Dimple

Traits A B AB O Positive Negative Roller Non-roller Free Attach Straight Wavy Curly Present Absent

Alleles p q - r p q p q p q p - q p qAllele

frequency 0.2 0.3 - 0.5 0.6 0.4 0.4 0.6 0.5 0.5 0.7 - 0.3 0.1 0.9

X2 Value X2 =5.08*, df=3 X2 =75.92*,df=1 X2 =1.08N.S, df=1

X2 =0.69 N.S, df=1 X2=43.46*,df=2 X2 =0.81 N.S, df=1

Discussion

As the result has shown the prevalence of B blood type in Punjab province of Pakistan followed by O, A and AB. We can deduce that the result is similar to Bangladesh and India (B>O>A>AB). (Dewan G., 2015 ; Chandra T, & Gupta A., 2012) but little difference in allelic frequency due to different ethnic groups and regions. Higher prevalence of blood group B in Punjab, Pakistan might be due to protection against disease because studies have shown that Cholera infections are particularly severe for blood group ‘O’ individuals (Holmner A, et al 2010 ; Glass RI., et al 1985). It was studied that Diabetes Type ΙІ is associated with blood group B, since the diabetic patient is more common in our population with blood group B. (Qureshi, M. A., & Bhatti, R. 2003). The blood type O is associated with malarial resistance which might have evolutionary advantage. The antigen present on the surface of RBCs (erythrocytes) of blood group A and B is presumed to act as a receptor to form a rosette structure. (Barragan A., et al 2000). While the lack of oligosaccharide on RBCs of blood group O have not suitable for rosette structure infected by Plasmodium falciparum but it is more sensitive to cholera disease. The combined study of ABO and Rh factor has shown the prevalence of B+ and least is AB- as shown in Fig 1.11 (B+ > O+ > A+ > AB+ > B- = O- > A- > AB-). The result for a blood group in male and female is significantly different from the expected population individually while non-significant for the whole population. This indicates that at least one assumption is violated from Hardy Weinberg equilibrium. The presence Rh (D) antigen is more frequent which is 86% compare with Indian population having 95.71% (Chandra T, & Gupta A 2012). It has observed that the frequency of Rh (D) is quite similar in both genders.

The present study showed population contains 28.53% attached ear lobe which is close to the result of Indian and Ekpoma Nigeria population containing 35.1% (Sharma, A,. et al 2007) and 31.61% (Ordu, K. S., et al 2014) respectively. Sixty percent of people in the Punjab population can roll their tongue which is approximately matched with the result of Razzaq et al (2015). The Punjabi and Saraiki collectively contribute 52.3% peoples which can roll their tongue. (Razzaq et al., 2015). In Punjab 24.03% population have dimple compare with the study of Razzaq et al (2015) has 33.5% in Punjabi and Saraiki population in Punjab.

In the three classes of hairs morphology, the result of straight (55.79%) and wavy (29.32%) phenotype of hairs are different with European population having 45% and 40% respectively, but the curly (14.89%) nature of hair is similar with the study in Europe (15%). It was reported that

Fig 1.11 Combined percentage of ABO and Rh factor in population

18%

5%

38%5%

9%

1%

20%

5%

ABO Blood type with Rh factor

A+ A- B+ B- AB+ AB- O+ O-

straight hair is specifically present in an Asian population frequently (Fujimoto et al., 2007; 2009).

Pakistan is a country having different ethnic groups and races. The study is mainly concern with the Punjab region of Pakistan. So, this region has no drastic variation within the population. It might be assumed that the result which is non-significant is due to because alleles are moving within the same population. Mainly this region has two ethnic groups Punjabi and Saraiki. These two groups have their own tradition, customs and language. Due to this, little variation which causes a significant result in the population. Further, migration and immigration of peoples from the Punjab region might cause significant result in some characters. Mutation and selection pressure might also have a role in disequilibrium the population.

Conclusion:

This study concluded that the alleles for nature of hair and dimple are not in equilibrium in the population. In the male, blood group, nature of hair and dimple while in female blood group, Rh factor and nature of hair are not in equilibrium.

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