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Stuy on inheritence pattern and frequency of genetic trait for earlobes
STUDY ON INHERITENCE PATTERN AND FREQUENCY OF GENETIC TRAIT FOR
EARLOBES AMONG THE ETHNIC GROUP (BRAHMIN) IN RAJAPUR,BARDIYA ,NEPAL
Submitted as a part of practical course of
Master of Science in Zoology Second Semester
Central Department of Zoology
Institute of science, and technology
Roll no:- 39
M.Sc. Second semester
CENTRAL DEPARTMENT OF ZOOLOGY
Earlobes also known as lobules auricular is the soft fleshy
lower part found at the base of the external ear. It is the only
part of the auricle not supported by cartilage (Richard D. L.
2005). It is composed of the tough areola and adipose (fatty)
connective tissues lacking the firmness and elasticity of the rest
of the pinna (Chummy 1999; Keith and Arthur 2006). It is either
attached directly to the lateral side of the head or detached
hanging freely away from the lateral side of head. The detached
type is slightly bigger than the attached earlobe Detached
earlobe is considered a dominant trait while attached one is
recessive. This variation in attachment of earlobe is a trait
inherited from parents and its inheritance follows a pattern.
The patterns of inheritance describes how a allele works
together to produce traits.
The patterns described includes ;
X-Y Linked traits
Dominant- Recessive inheritance
X-Y Linked inheritance results when the gene is located
in the sex chromosome (X or Y).
In polygenic inheritance, a trait is controlled by multiple
gene pairs. So there is a gradual variation of the trait in
the population without a clear distinction. Examples include
height, color etc.
Mitochondrial inheritance is when the chromosome is
located in the mitochondrial of the cell instead of the nucleus
like in the egg cells of humans (Nussbaum et al. 2007).
Dominant- Recessive inheritance involves two pairs of
contrasting characters (allele) controlling one trait where
recessive allele is masked by the dominant when they occur
together. The recessive can only manifest in homogeneous
form (Molly and Hougeton 2010).
Ear lobe attachment is a morphogenetic trait. There is
conflict in the decision whether earlobes attachment is
controlled by a single gene (Anshu et al. 2007) or influenced by
many genes- a polygenic inheritance pattern (Dutta and
Ganguly 1965) .
Table 1: Dominant- recessive Inheritance pattern of earlobes
S.N. Father Mother Offsprings RATIO:
DOM. ( EE)
1. When Both Father and mother are with attached earlobes
a. ee ee - - ee 0:1 0:1 0:0:1
2. When Father with attached earlobes and mother with detached earlobes
a. ee EE - Ee - 1:0
b. ee Ee - Ee ee 1:1 0:1:1
3. When father with detached earlobes and mother with attached earlobes.
a. EE ee - Ee - 1:0
b. Ee ee - Ee ee 1:1 0:1:1
4. When both Father and mother with Detached earlobes.
a EE EE EE - - 1:0
b Ee EE EE Ee - 1:0 1:1:0
c EE Ee EE Ee - 1:0 1:1:0
d Ee Ee EE Ee ee 3:1 1:2:1
• To calculate the frequency of genetic trait (attached and
• To know the inheritance pattern of genetic trait (attached and
• Difficult to collect data from whole community
• Unable to study on genotype level.
Materials and Methods
• Direct interaction with people.
Data were collected starting with the children, then the mother
and finally the father and arranged and is analysed. the expected
frequencies are calculated from expected ofspring ratios from the
mendellian crosss between different parental combinations given in
table 1. Using chi-test, the significance of the observed
frequencies are tested at p<0.05 (critical value=3.84;and degree of
freedom=1) as shown in table 3.
• Rajapur is located in mid-western region of Nepal which is also
known as island of Nepal which is bounded by Karnali river.
Majority of people are Tharu and Brahmins were immigrants from
different mountanious area were choosen for the study.
Family Individual Name Gender Detached earlobe Attached earlobe
Table 2: Observation of attached and detached earlobes in Rajapur, Bardiya
Total Number of Offspring Chi
Detached Attached Total
8 16 8 24 3.84 0.889 Accept
9 17 10 27 3.84 2.09 Accept
24 63 5 68 3.84 0.1401 Accept
4 1 8 9 3.84 - -
Total 45 97 31 128
Table 3:- Frequency table showing offspring with attached and detached earlobes with
their respective parents.
• Total Population: 218
• People with Detached earlobes: 162
• People with Attached earlobes: 56
Frequency of Detached earlobes=Number of Detached Earlobes×100%
= 162 × 100%
Frequency of Attached earlobes= Number of Attached earlobes ×100%
= 56 × 100%
Attached earlobes Detached earlobes
Fig. 1:- Percentage of Brahmins people of Rajapur, Bardiya with detached
and attached earlobes.
Out of 218 individuals of 45 families used 74.31% had
detached earlobes while 25.68% had attached earlobe in the
ratio of 3:1 . This is similar to the Mendelian monohybrid
inheritance using the punnet square. But this result is in
contrast to the study amongst the Chinese and Japanese that
recorded 66.6% for attached earlobes (Lai and Walsh 1966).
It agrees with a record of 35.1%, 4.67% and 31.61% for
Indian, Jats of Delhi and Ekpoma Nigeria populations for
attached earlobe respectively (Sharma et al. 2007).
The current study also conforms to the result of Barut
and Aktune (2006) where they found that 78.4% of Turkish
students had detached earlobe.
Sixty three offspring had detached earlobe and Five had
attached earlobe when both parents had detached earlobe
(Table 3) with a high ratio of 13:1. Thirty three offspring had
either parents with detached earlobe as shown in Table 3.
These agree with the crosses shown as table 1.
One offspring had detached earlobe and Eight offspring
had attached earlobe when both parents had attached earlobe.
The one offspring is deviation from the cross shown in table
which is statically not significant at p<0.05. This suggests that
they occurred by chance and might not be true biological
children of these parents (Ordu et al. 2014). Therefore is in
conformity with single gene Mendellian dominant-recessive
The inheritance pattern then is unlikely to be sex linked or
mitochondrial inheritance but rather controlled by autosomal
genes which are recessive for attached and dominant for detached
Variations in the sizes of earlobes was observed amongst the
individuals and within families which might suggest polygenic
inheritance, these earlobe variations are due to the
differences in the ages of offspring since earlobe increases with
age (Anshu et al. 2007) and not polygenic inheritance which is a
great find in opposite of Dutta and Ganguly (1965) who concluded
that earlobes attachment is polygenic inheritance.
Therefore the pattern of inheritance amongst brahmins is
a dominant recessive single gene Mendellian pattern which was
also found to be same in Nigerian tribe found by Williams and
Hughes (2008) and Ordu et al. (2014).
The present study provides comprehensive database of 218
samples of 45 families on the inheritable trait for Detached
earlobes and attached earlobes people of Brahmins of Rajapur,
From the above results, it has been found that the presence of
Detached earlobes people have higher frequency about 74.31%
are the dominant and attached earlobes people about 25.69% are
the recessive .
On the basis of data of this community it is seen that the most
of the Brahmins of Rajapur, Bardiya have dominant Detached
earlobes and inheritance pattern is of simple dominance-recessive
Firstly, I would like to express my immense gratitude to our
respected Associate prof. Dr. Nanda Bahadur Singh and Associate prof.
Dr. Kumar Sapkota for a great encouragement, motivation and
suggestion during the planning and preparing of this report. In
addition to this, I would like to thanks Prof. Dr. Ranjana Gupta, the
Head of the Department of Zoology, Tribhuvan University.
This report includes the data and information on human trait
for earlobes that transferred from parents to their offspring genetically
I would also like to thanks to the Brahmin Community of
Rajapur, Bardiya for supporting and providing me the data for this
Lastly i would like to express my gratitude to Miss Binita
Pandey for helping me for preparation of this report and to all my
classmates for their valuable cooperation and comfortable relation.
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