Wild type body and Black body
Table 2.2.3
Table 2.2.4
Chi-squared test statistic: 0.972
The punnet square of the black body also show the norm as both F1 and F2 match up in ratios with all the other crosses. Black coloured body and Ebony coloured body are the only two coloured body crosses that aren’t affect by sex. i.e. a particular gender doesn’t drop out that has a particular set of genes. This is probably due to the fact that this cross is more stable in that it doesn’t have any diseases associated with it. This means that any wild type can cross with any black body type and none of the offspring will be affected. The “observed” value is very close to the “expected” value based on Mendel’s ratios. The Chi squared value is again well over 0.05 meaning that the hypothesis proposed based on Mendel’s ratios is likely to be true. The wild types ratio to the black body type is 3:1 when the numbers are added. The level of significance concerning the wild type and black body colour is fairly high which also supports the hypothesis proposed. This means that there is roughly an 80% chance of the hypothesis proposed being true.
Wild type body and Ebony body
Table 2.2.5
Table 2.2.6
Chi-squared test statistic: 2.1316
Ebony coloured body is very similar to Black coloured bodies results and is also similar in that none of the genotypes make a particular gender drop out in the cross with a particular set of genes. i.e. none of the females dropped out in the cross because the cross was more stable and there were no diseases in the cross. Likewise to black bodies results the observed and expected value are very close to each other and the chi squared value is well over 0.05 meaning that the hypothesis proposed in this cross is also likely to be true. Also note that the chi squared value for this particular cross is unusually high in comparison to the other crosses. The results are similar but the chi squared value is still unusually high and substantially higher than the other crosses. The level of significance is considerably low especially when the chi squared value is so high. Roughly there is a 54% of the hypothesis proposed happening in real life.
Wild type body and Sable body
Table 2.2.7
Table 2.2.8
Chi-squared test statistic: 0.0179
Sable coloured body, yellow body and tan body are much the same in results to each other. The all have only 3 genders come out after the F2 cross. This could be due to a disease affecting the female with the recessive trait. These three colours all have the same 3:1 ratio of wild body colour to their own colour. They all have close “observed” values to the “expected values based on Mendel’s law of segregation. The only difference between these three colours other than the obvious colour difference is that Sable body colour has an extremely low Chi squared value. Even though the data is similar this is the only cross out of all five crosses made that has a low than 0.05 chi squared value. The lower chi squared value resulted in a high level of significance with about a 90% chance of this cross happening in real life.
Wild type body and Tan body
Table 2.2.9
Table 2.2.10
Chi-squared test statistic: 0.4705
Tan body is also very similar to sable and yellow coloured body. The results from the simulation followed the same pattern as the other. The results were in a 3:1 ratio for wild body colour to Tan body colour, the chi squared value is well over 0.05 and the “observed” value is very close to the “expected” value based on the ratio of 3:1. The level of significance value for the tan body colour and wild type was just below 50% but is close enough to still support the hypothesis tested.
In conclusion of part A all the results conformed to the expected ratio of 3:1 outlined in Mendel’s law of Segregation. The dominant allele was always the wild type and the recessive was always the different colours. All chi squared values were above 0.05, with the exception of sable body colour, suggesting that the proposed hypothesis was likely to be true. The sable body colour had an unusually low chi squared value. All the other crosses had chi squared value between 0.4 and 0.9 making the chi squared vale for sable very low. Also the Chi squared value ebony did not fit in between 0.4 and 0.9 it was opposite to sable in that it had an extremely high chi squared value within comparison to the other crosses. All the data collected from the simulation had all a very close ratio of wild type to the colour of 3:1 and reasons for sable and ebony to have very abnormal chi squared values within comparison to others. Some of the crosses Tan, Yellow and Sable body colours did not have females for the recessive trait. E.g. there were no yellow body coloured females. A suggestion for this happening is that there may be a disease that affects the flies that have a two X chromosomes for that particular trait. All the data collected fitted into what was expected to happen (3:1 ratio) with only minor differences in values such as the chi squared value. The level of significance values are all fairly high above 50% meaning that there is a 50% chance or more of these crosses happening in real life.
3 DATA COLLECTION and PROCESSING
Part B
3.1 Raw Data: Mendel’s Peas
Monohybrid Cross
The monohybrid cross will be performed using the characteristics wrinkled or round. Each parent or coin in this experiment will represent a heterozygous mix of the alleles W for round or w for wrinkled. The Dominant gene is round and the recessive is wrinkled. All the possible outcomes are below in a table. As can be seen the theoretical ratio of round to wrinkle is 3:1. This is Mendel’s second law of segregation. This cross will be simulated using coins. Each side of the coin will represent either a W or a w as the parents (coin) is heterozygous. The coins will be tossed 32 times and the results will be in the form of a table.
Table 3.1.1
Table 3.1.2
The table above shows the observed crosses against the expected number of crosses. The expected value is based on the 3:1 ratio put forward by Mendel in his law of segregation. As can be seen the “observed” value is very close to the “expected” with only a minor difference in numbers.
Dihybrid Cross
Table 3.1.3
In the tables above is a replication of what each coin will have on it. The table on the left is what the possibilities of the first toss of the two coins. This will then be added to the second toss of the two coins. The two different coins represent two parents with heterozygous gametes. This will make up the genotypes of the Dihybrid cross. Below are all the possible outcomes for a Dihybrid cross between round or wrinkled and green or yellow. As can be seen it is in a 9:3:3:1 ratio
Table 3.1.4
Table 3.1.5
The table above shows the results of the coin tossing. The “expected” results are based on Mendel’s ratio of 9:3:3:1. As can be seen the “observed” value is very close to the “expected”, with only minor differences in the numbers.
3.2 Processed Data
The chi squared test is a test to measure goodness of fit. This is relating to the hypothesis tested. It is used to demonstrate statistical significance. Chi squared is used so that is can be fairly sure that the results obtained are not due to pure chance. In this situation it is being used to test goodness of fit by establishing if the observed values are relate to the expected values based on Mendel’s ratio of 3:1.
The formula for Chi Square is:
Where
x2 = the Chi-square value
Oi= the observed value
Ei= the expected or theoretical value
There fore (sample chi squared of monohybrid round peas)
X2=(28-24)2/24
X2=(4)2/24
X2=0.667
All of the Chi squared results are in the tables below. The totals of all the Chi Square values are also shown in the table below.
Monohybrid Cross
Table 3.2.1
The monohybrid cross results are shown above in the table. It can be observed that “observed” values and the “expected” values for the experiment are very close. The “expected” values are based on Mendel’s 3:1 ratio. The chi squared has been individually calculated for the dominant and recessive gene. The chi squared value is above 0.05 suggesting the hypothesis tested to be likely.
Dihybrid Cross
Table 3.2.2
The Dihybrid cross results, shown in the table above, were as expected. They nearly match the ratio of 9:3:3:1 which Mendel stated would be the ratio for a dihybrid cross. All “observed” values are very close to the “expected” values. The chi squared values are all over 0.05 suggesting that the hypothesis tested to be likely.
4 Conclusions and Evaluating
Part A & B
Conclusion statement
In conclusion in both part A and part B all crosses were in the expected ratios. There were no major deficiencies in the data. All the chi squared values were over 0.05 with the exception of one. This was the ebony coloured fly in part a. The data associated with the ebony coloured fly was also similar to the other flies data and so it is uncertain why there was such a small chi squared value. The chi square data supported the hypothesis in both parts A and B. the level of significance also supports the hypothesis no part A. All of the level of significance values were large also supporting the hypothesis tested.
Evaluating procedures
The procedure used for this experiment concerning the Drosophila was reliable as it was a simulation based on real life results. This experimental procedure for part B could have been better as it was using probability to select the genes and while this is somewhat true in real life when crosses are made it isn’t completely due to pure chance that a particular gene is passed on. As it was using coins to represent genes it is theoretically possible for all the peas to turn out with the recessive genes, although this is highly unlikely it is still possible due to chance.
Reliability
The experimental results were fairly reliable as this was a simulation based on real results. All of the level of significance and chi square values supported the hypothesis and suggest that it was more than likely. The reliability of the results associated with part A was a lot higher as part B relied more on probability and chance. Part B’s chi squared values were all high resulting in a very low level of significance. A low level of significance suggests that the hypothesis test is not likely to be true but this has an error associated with it as part B was more probability and chance.
Limitations/ weaknesses/errors in laboratory investigation
The main limitation concerning part A was that it was a simulation, and although the results are based on real life results there could still be a computer error when everything was being calculated. The main limitation concerning part B is that it was using coins and probability and chance. A better way to do this would have been to plant the peas and observe them grow etc. Although this would take much longer it would end in better results and more discussion.
Significance of weaknesses on experimental results
The main weakness of this experiment would be in part B as part A was based on real results in real life. Part B was based more so on probability and chance then on actually inheritance and genetics.
Improving the investigation
The investigation could have been improved if instead of coins in part B if Mendel’s actual experiment was replicated. This would have ended in better, more reliable results and more discussion.
Modifications to experiment
There were no modifications to the experimental design as it was a simulation. All instructions were followed as outlined in the cover sheet.
Casey Going
Mr Craig-Ward
Biology IA
