Study on certain Human Traits based on Hardy – Weinberg’s Principle

 

Pranay Punj Pankaj¹, Sant Kumar Khandekar², Swati Sahu³, Arvind Agrawal⁴*

¹Department of Zoology Nagaland University Lumami- 798627

²Department of Zoology Govt. Larangsai lead P.G. College Ramanujganj (C.G.)

³Department of Zoology Govt. K.H. College, Abhanpur (C.G.)

⁴Human Resource Development Centre, Pt. Ravishankar Shukla University, Raipur - 492 010

 

ABSTRACT:

The aim of this paper is to discourse the Hardy-Weinberg (H-W) Law by investigating some selected morphological traits of participants and their relatives of Orientation programme- January 2017, Human Resource Development Centre, Pt. Ravishankar Shukla University, Raipur, India in which data have been collected by analyzing certain autosomal genetically transmitted morphological characters. As per H-W Law, Allele frequencies will remain constant over generations if there is no genetic drift, random mating, mutations, etc. having gene frequencies are p and q, the genotype frequency will be p², 2pq, q² respectively for the dominant, heterozygotes and recessive. In this present study total of fifteen autosomal genetically transmitted morphological characters were analyzed to see whether the distribution of morphological characters follows H-W Principles or not from 32 samples of age groups from 25 to 55 males and females. Chi square test and p values were done to have a clear view about difference in observed and expected allele frequencies. Maximum dominant characters were observed in morphological traits like handedness and eye shape which were about 29 out of 32 whereas minimum dominant characters were observed in morphological trait like dimples which was about 7 out of 32. Maximum heterozygous trait was seen in ear lobe morphological trait whereas least heterozygous were seen in morphological trait of dimples. The results showed lesser degree of deviation than expected on application of chi square test hence, establishing that certain forces like natural selection, genetic drift, non-random mating etc. have no effect.

 

 

 

INTRODUCTION:

All people are recognizably human, but no one is exactly alike, not even an identical twin therefore, we all exhibit uniqueness. No doubt, we share some common characteristics with our family members, even though every one of us has a unique combination of traits. Some traits are controlled by genes which generally pass from parents to children while others are acquired through learning. A single gene has two alleles; each allele producing a distinct phenotype, but mostly we are influenced by a combination of genes and environmental factors (Feuket al., 2006).

 

Further, the Hardy-Weinberg principle, states that allele and genotype frequencies in a population will remain constant from generation to generation if a population is undergoing no evolutionary change. The percentage of homozygous and heterozygous individuals remains constant over the generations. But in fact, a particular population may not be in equilibrium at a particular time. In such cases, distribution of alleles in succeeding generations is the result of random mating (Wakeley et al., 2016).

 

The present study is refers to distribution of traits and frequency of gene in an population and how genetic variation is created or shaped over time and eventually leads to an evolutionary change, adaptation and speciation. So it deals with the changes in allele frequencies. Starting point frequency of different alleles is recorded by population geneticists. The frequency is measured at intervals. Any deviation from the previously recorded frequency indicates the degree of evolutionary change caused by variations. Therefore here we aim to study the morphological traits of participants and their relatives of Orientation programme- January 2017, Human Resource Development Centre, Pt. Ravishankar Shukla University, Raipur. The recessive genotype presents without a cleft. However, it is also a classic example for variable penetrance with environmental factors or a modifier gene possibly affecting the phenotypical expression of the actual genotype. Cleft chins are common among people originating from Europe and the Middle East (Nadeau, 2001).

 

REVIEW OF LITERATURE:

Ancient history reveals that pre-scientific knowledge regarding inherited differences between humans has been existed since early times. Greek physicians and philosophers have reported such observations and developed theoretical concepts and eugenic measures (Provine, 1978). “The History and Geography of Human Genes” By Xu et al (2002) quote that “Thirty years ago, the first attempt was made to reconstruct the history of human differentiation by employing the genetic divergence observed among human groups” (Xu et al., 2002). Living organisms are endowed with unique abilities, traits that allow them to survive in a given environment. These traits or abilities may show or exhibit enormous variations within species and across species. Some of these traits are unique to that species; some traits are common within and across species with little variation, these are adaptive characters and gives survival advantage. The nature of heredity of some of these traits could be complex and/or it could follow some simple principles of transmission. Despite a century of research on complex traits in humans, the relative importance and specific nature of the influences of genes and environment on human traits remain controversial (Feuket al., 2006).

 

Carrière (1922) was among the first to study the genetics of earlobes, and they reached opposite conclusions. Carrière (1922) looked at 15 families and concluded that attached earlobes were dominant. Powell and Whitney (1937) looked at one family and concluded that attached earlobes were recessive. Hersh et al. (1953) identified 51 families in which one or more children had bent little fingers. In 47 of the families, one parent had bent little fingers and the other had straight. Hersh et al. (1953) concluded that bent little finger was caused by a single dominant allele, but the four families in which both parents of a B child were S are inconsistent with this. Dutta (1965) found two extended families with bent little fingers. Dimples vary in how obvious they are. Wiedemann (1990) suggests that their appearance may be affected by circulation, body weight or muscle tone, although he does not cite any evidence for this. Cleft chins come in a variety of shapes, including vertical furrows, Y shaped furrows, and round dimples (Günther, 1939). They also vary in depth from barely noticable to extremely prominent (Bhanu and Mahhotra, 1972). The frequency of cleft chin varies widely among different populations; Indian populations range from 4 to 71 percent cleft chin (Bhanu and Malhotra (1972). Günther (1939) recorded cleft chins in 9.6 percent of German men and 4.5 percent of German women. Most people have a strong preference for clasping their hands in one way, either with the left thumb on top (L) or the right thumb on top (R). Surveys indicate that roughly half of the people studied are R and half are L (Wiener 1997, Freire-Maia et al. 1988, Lai and Walsh 1985, Reiss, 2001). Reiss (2001) reviewed nearly 100 publications that have surveyed hand-clasping frequencies in populations around the world. There were a few populations with particularly high or low frequencies of left-over-right claspers, but most populations had between 40 and 75 percent L. Harris and Joseph (1999) measured the angle between the first and second phalanges of the thumb on X-rays of 294 individuals. Glass and Kistler (2005) arbitrarily called all thumbs with an angle equal to or greater than 50 degrees "hitchhiker's thumbs." Glass and Kistler (2005), having decided that anyone with one or both thumbs having an angle equal to or greater than 50 degrees had the hitchhiker's thumb trait. Some studies have found about 5 percent of the populations sampled to have the big toe and second toe equal in length (Romanus, 1999). Hawkes (1987) said the big and second toes were the same length in only 0.1 percent of people.

 

The proportion of people who can roll their tongue ranges from 65 to 81 percent, with a slightly higher proportion of tongue-rollers in females than in males (Sturtevant 1940 and Glass and Kistler, 2005). However, some people, especially children, cannot roll their tongue when first asked but later learn to do so (Sturtevant 1940). Komai (2002) found that the proportion of tongue-rollers among Japanese schoolchildren increased from 54 percent at ages 6-7 to 76 percent at age 12, suggesting that over 20 percent of the population learns to tongue-roll during that age range. Lee (2003) looked at photographs of male medical students and concluded that 32 out of 1039 (3%) had a "slight but noticeable" widow's peak and one had a "more distinctive and obvious" widow's peak. Nusbaum and Fuentefria (2009) looked at 360 women in hair salons and concluded that 81% of them had a widow's peak. Since last few years’ extensive efforts have been made to catalogue human genetic variation and correlate it with phenotypic differences. Although these studies have provided new biological insights, only a limited amount of the heritable component of any complex trait has been identified and it remains a challenge to elucidate the functional link between associated variants and phenotypic traits.

 

METHODOLOGY:

Survey based study: Survey based study of participants and near relatives of Orientation programme- Jan 2017 held at Human Resource Development Centre, Pt. Ravishankar Shukla University, Raipur, India in which data have been collected by analyzing certain autosomal genetically transmitted morphological characters (Kohli et al., 2015).

 

Hardy Weinberg’s Principles:

Fifteen autosomal genetically transmitted morphological characters were analyzed to see whether the distribution of morphological characters follows Hardy Weinberg’s Principles or not from 32 samples of age groups from 25 to 55 males and females (Joshi, 2008).

 

Chi square analysis:

Chi square test and p values were done to have a clear view about difference in observed and expected allele frequencies (Engels, 2009).

RESULTS AND DISCUSSION:

Table 1: General list of characters taken into account

SN	Human Traits	Dominant/Recessive
1	Cleft in chin	No cleft dominant, cleft recessive
2	Dimples	Dimples dominant, no dimples recessive
3	Earlobes	Free lobe dominant, attached recessive
4	Tongue rolling	Roller dominant, non-roller recessive
5	Tongue folding	Inability dominant, ability recessive
6	Hairline	Widow peak dominant, straight hairline recessive
7	Hair curl	Straight/Wavy dominant, Curly recessive
8	Bent little finger	Bent dominant, straight recessive
9	Interlaced fingers	Left thumb over right dominant, right over left recessive
10	Fingers (Index Shorter/ Longer or equal)	Index Shorter dominant, Longer/equal recessive
11	Hitch-hiker's thumb	Straight thumb dominant, hitch-hiker thumb recessive
12	Handedness	Right handed dominant, left handed recessive
13	Toe	Longer 2nd dominant, Shorter 2nd
14	Eyebrow shape	Separated dominant, joined recessive
15	Eye shape	Almond dominant, round recessive

 

 

Table-2: List of distribution of morphological characters in the population (N=32)

 

 

Hardy Weinberg’s principle:

p² + 2pq + q² = 1 and p + q = 1

p = frequency of the dominant allele in the population

q = frequency of the recessive allele in the population

p² = percentage of homozygous dominant individuals

q² = percentage of homozygous recessive individuals

2pq = percentage of heterozygous individuals

 

 

CHI - SQUARE (X²):

X2 = Σ(O - E)² / E

Observed Number of Individuals of Each Genotype:

p²= Observed Genotype Frequencies of p² × Total no of Population

q²= Observed Genotype Frequencies of q² × Total no of Population

2pq= Observed Genotype Frequencies of 2pq × Total no of Population

 

Table-3: Genotype Frequencies of distribution of morphological characters in the population

 

CHI - SQUARE (X²):

X2 = Σ(O - E)² / E

X2 = 5.873

X2 (calculated) <X2 (table) [16.919, 9 df, 0.05 ls].

Therefore, it is concluded that there is no statistically significant difference between observed and expected under Hardy-Weinberg. It is fail to reject the null hypothesis and conclude that the population is in Hardy-Weinberg Equilibrium.

 

Total 32 samples of individuals were analyzed from participants and their relatives of Orientation programme- January 2017, Human Resource Development Centre, Pt. Ravishankar Shukla University, Raipur, India considering 15 morphological characters. Maximum dominant characters were observed in morphological traits like handedness and eye shape which were about 29 out of 32 whereas minimum dominant characters were observed in morphological trait like dimples which was about 7 out of 32. Maximum heterozygous trait was seen in ear lobe morphological trait whereas least heterozygous were seen in morphological trait of dimples (Table 1, 2). Hardy Weinberg’s principle (p2 + 2pq + q² = 1 and p + q = 1) applied to get the p = frequency of the dominant allele in the population; q = frequency of the recessive allele in the population; p² = percentage of homozygous dominant individuals; q² = percentage of homozygous recessive individuals; 2pq = percentage of heterozygous individuals then genotype frequencies of distribution of morphological characters were observed in the population (Table3).

 

Allele Frequencies of distribution of morphological characters in the population were calculated assuming the formulae (Freq of p = p² + 1/2 (2pq); Freq of q = 1-p) then earlobe has got maximum heterozygoys. Expected number of individuals of each genotype were calculated using the formulae: p²= Expected Genotype Frequencies of p² × Total no of Population; q²= Expected Genotype Frequencies of q2 × Total no of Population; 2pq= Expected Genotype Frequencies of 2pq × Total no of Population then almost all human trait was found to be differ from observed value. Chi – square were employed to calculate whether the value is significant or not. Then it is concluded that there is no statistically significant difference between observed and expected under Hardy-Weinberg. It is fail to reject the null hypothesis and conclude that the population is in Hardy-Weinberg Equilibrium (Table 3). With random mating in large population H-W Equilibrium occurs after one generation provided that the same gene frequency occurs in both sexes. H-W Equilibrium implies that from generation to generation gene and genotype frequencies remain constant. If there’s any disequilibrium, equilibrium will be re-established after one generation of random mating. The HW Equilibrium also imply that if the gene frequencies are p and q, the genotype frequency will be p², 2pq, q² respectively for the dominant, the heterozygotes and the recessive in a two allele system. This can be inferred by the arguments given for the recessive type under dominant inheritance. By using the multiplication rule for probabilities the expected numbers for H-W Equilibrium can be calculated. The survey was based on 15 morphological characters to analyse whether inheritance of these characters followed Hardy Weinberg’s principles or not. In this present study total 32 samples of individuals were surveyed taking 15 genetically transmitted morphological characters into account to find out whether their distribution and transmission followed Hardy Weinberg’s law or not.

 

CONCLUSIONS:

It was observed that participants and their relatives of Orientation programme- January 2017, Human Resource Development Centre, Pt. Ravishankar Shukla University, Raipur, India showedlesser degree of deviation than expected on application of chi square test hence, establishing that certain forces like natural selection, genetic drift, non random mating etc. have no effect. As the test statistics exceeds critical value of chi square test (X²), the null hypothesis i.e. there is no difference between distributions was rejected with the selected level of confidence and alternative hypothesis that there was difference between distributions was expected with selected level of confidence. As the degree of deviation is greater it is expected that it is due to not only chance but also the certain forces (natural selection, mutation, genetic drift, non random matingetc.) acting upon them.

 

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Received on 09.03.2017                             Accepted on 05.06.2017

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