Part A: Data Collection, Presentation And Analysis
Many human features are controlled by a single pair of alleles, one dominant and one recessive, that are inherited in simple Mendelian fashion. To examine this further, a survey was done on two of basic human features.
The two phenotypes chosen for the survey were hand clasping (left over right being dominant) and tongue rolling (where the ability to do so is dominant). Fifty people from a variety of demographics were surveyed. The table below shows the results of the survey.
Table 1: Survey Results
Tongue Rolling Hand Clasping Tongue Rolling Hand Clasping
1 Y R 26 Y L
2 N R 27 N L
3 Y R 28 N R
4 Y L 29 Y R
5 Y L 30 N R
6 N L 31 Y L
7 Y L 32 N L
8 Y R 33 N L
9 N L 34 Y R
10 Y R 35 Y R
11 N R 36 Y L
12 N R 37 N R
13 Y R 38 Y L
14 Y L 39 Y R
15 Y L 40 N L
16 Y L 41 N L
17 N R 42 N L
18 N L 43 Y L
19 N L 44 Y L
20 Y R 45 Y R
21 N R 46 Y R
22 Y R 47 N L
23 N L 48 N L
24 Y L 49 Y L
25 Y R 50 Y L
The following table shows the two alternative phenotypes for each characteristic, each phenotype’s possible genotypes, and the frequency and relative frequency of each phenotype in the sample above. The relative frequency is the frequency divided by the total number of people (in this case fifty) then multiplied by 100 to be expressed as a percentage.
Table 2: Survey Frequency Table
Tongue Rolling Hand Clasping
Alternative Phenotypes Able to roll tongue Unable to roll tongue Left thumb over right Right thumb over left
Possible Genotypes RR, Rr rr CC, Cc cc
Frequency 29 21 28 22
Relative Frequency 58% 42% 56% 44%
The graph below is a visual representation of the relative frequency table above.
Figure 1: Graph of Relative Frequencies
As can be seen in Figure 1, the dominant gene for both tongue rolling and hand clasping is only slightly dominant in the surveyed sample. For tongue rolling, the phenotype of being able to roll the tongue was more common (58% to 42%) than the phenotype of being unable to roll the tongue. For hand clasping, the phenotype of the left thumb resting over the right thumb was more common (56% to 44%) than the phenotype gene of right over left.
Tongue Folding Data Analysis
A common misconception is that dominant phenotypes occur at a higher frequency in the population. This is not necessarily true. For example, the gene for tongue folding is dominant; however, in a sample of 26 people, only 9 of them could fold their tongue.
Table 3: Tongue Folding Sample Results
Alternative Phenotypes Able to fold tongue Unable to fold tongue
Possible Genotypes TT, Tt tt
Frequency 9 17
Relative Frequency 35% 65%
As can be seen in Table 3, the dominant gene of tongue folding only surfaced in 35% of the sample, which is less than the recessive gene (65%). The fact that the gene is dominant only means that it will dominate the other gene (as with Tt, the phenotype...