5. DISCUSSION:
Variation refers to any differences between organisms caused either by genetic
differences (genotypic variation) or by the effect of environmental factors on the expression of
genetic potentials (phenotypic variation). In other words phenotypic variation is basically all the
obvious differences of physical appearances and behaviour of organisms while genotypic
variation is the differences in the genes which are not easily seen by the naked eye.
Phenotypic Variation can be classified into two levels; intraspecific and interspecific
variation. Variation occurring between different species is called interspecific and is commonly
used by biologists when classifying organisms. Intraspecific variation is the differences within
the same species. This type of variation can be described as either being discontinuous or
continuous.
Discontinuous Variation is where individuals
A chi square test is a statistical method of assessing and comparing the observed data and
the expected data. In the experiment a chi square test was used to determine the frequency of the
phenotypes with comparison to Mendel law of assortment. Our null hypothesis was that there
was that there are no significant difference between the observed and expected results and was
determined using the chi square test. The chi square table was entered at d.f =3 and we saw that
the probability of our chi square value is greater than 0.9. By statistically convention we used the
0.05 probability level as our critical value. If the value is greater than the 0.05 value (2.37) the
hypothesis will be rejected; however since the value obtained was less than the critical value the
null hypothesis was accepted that the data fits a 9:3:31 ratio. From the results obtained it can be
concluded that Mendel law of independent assortment was indeed valid.
In the experiment, 4 coins were labelled on each side. On the first two coins , they were
labelled as follows ; one coin had a capital ‘A’ which represents a dominant gene on one side and
an common ‘a’ to represent a recessive gene. The combination of ‘Aa’ on the coin represented a
heterozygous genotype. The other coin was labelled using B instead of A to show a different
gene/ phenotype; hence a dihybrid test could have been conducted. These two coins represented
two different heterozygous genotypes of the first parent. The other two coins were labelled
similarly as the first two and represented the second parent. This was necessary because in order
6. to investigate Mendel 2nd law of assortment a dihyrbid cross test must be conducted using two
heterozygous genotypes.
From the results obtained from the class there is a general trend where the value from
‘dominant in both’ is substantially the largest and both the values of ‘Dominant in the 1st and
recessive in the 2nd’ and ‘Recessive in the 1st and dominant in the 2nd’ and similar and the value
from ‘Recessive in both’ is the lowest. This trend follows the genotypic ratio of Mendel’s Law
9:3:3:1.
SOURCES OF ERROR:
The fact that the surface which the coins were flipped on weren’t smooth flat surfaces
this may have caused disturbance in the coins.
PRECUATIONS:
The tape was evenly cut to prevent any uneven distribution in the weight of the coins.
Also all the coins used were the same size. The letters used in the labelling of the genes
were letters which can easily be distinguish from each other.
LIMITATIONS:
A pencil was used instead to label the coins which resulting into the records taking a lot
more time because the letters weren’t clearly seen.
CONCLUSION:
From the experiment we can conclude that Mendelian phenotypic ratio (9:3:3:1) was indeed
valid between two di hybrid heterozygotes genotypes due to the value which was obtained from
the chi square test being 1.93 being less than our probability number 2.37 and as a result the null
7. hypothesis that there are no significant differences between the observer and expected results
was accepted.
