Genetic Analysis in Plants

Abbey Emmanuel and Danielle Peterson

Life 120—Lab Section 136

October 29, 2014

Introduction Every living organism is made up of a series of genes. Each characteristic, such as color and texture, rely on the genetic coding of the organism. These genes can be passed along, mixed with other genes, or removed throughout the generations. The process of traits being passed from parent to offspring is called gene transmission. (Bailey, 2014) In the 1860’s a monk, Gregor Mendel set basic principles for heredity. His first law was Mendel’s law of segregation. He discovered this law while studying pea plants. He studied a series of seven different traits. (Bailey, 2014) He first observed and confirmed through experimentation that one pea plant of a certain color could self fertilize and produce another pea plant of the same color. He referred to the process of these self-fertilizing pea plants as true-breeding. (Urry et. Al, 2014) Mendel continued his studies of pea plants by testing that outcome of cross-pollination between two true-breeding plants. He took the two parent plants, one green and one yellow, and found the offspring to be all green. He continued experimenting by crossing two of the offspring from the first generation plants. Mendel found that in the second generation, an offspring color appeared from the parents that were lost in the first generation. His law of segregation explains that allele pairs segregate during the formation stage, but are capable of uniting during the fertilization stage. (Bailey 2014) Offspring inherit specific genes from their parents to obtain a certain identity through reproduction. The offspring have a specific DNA encoding within each gene that is made up of a sequence of nucleotides. These nucleotides are placed at a locus somewhere along a precise chromosome. (Urry et. Al, 2014) Differentiations of the same gene are called alleles. Alleles cause different traits in the offspring. (Metzler, K)
A living organism’s observable traits are called phenotypes. Phenotypes include both physical appearances and physiological traits of the organism. An offspring can inherit dominant traits or recessive traits. A dominant trait trumps a recessive trait during reproduction. Therefore, if a dominant, homozygous green seedling were to cross with a recessive albino seedling, the expected offspring color would be green.
The seedlings can also be homozygous or heterozygous. Homozygous means that the plant’s genotype has a pair of identical alleles in a gene, such as PP or pp. A heterozygous organism contains two alleles that are not the same for a gene, such as Pp. (Urry et. Al, 2014)
Based on our knowledge of genetics and inheritance, we predicted to observe one albino corn seedling to every green seedling. In corn, the dominant allele controls the production of chlorophyll. Our experiment contained two heterozygous parents that contained the chlorophyll gene.
In our analysis of a di-hybrid cross, we hypothesized an outcome with the majority being purple, smooth corn kernels. Our hypothesis is this because purple is the dominant kernel color over yellow, and smooth texture is the dominant allele over rough texture.
During our soybean seedling experiment, we hypothesized an outcome with a ratio of 1:2:1 for the color of the seedling leafs. We expect to see two light green leafs, to every one yellow and dark green leaf. The yellow leaf is expected because of a mutation among the soybean plants. The cotyledon color is hypothesized to have three seedlings with green cotyledons to every one seedling with a yellow cotyledon.
Materials and Methods
Green and Albino Corn Genetics First, we obtained one hundred heterozygous corn seeds and planted them in a flat. The flat was placed in an environment where the corn seeds could thrive and grow. Once the seeds germinated, we counted the total number of seedlings. We separated them into two different categories: green seedlings and albino seedlings. We documented the number of seedlings found in each category into our chart for further analysis.
Analysis of a Di-Hybrid Cross in Corn First, we obtained a container filled with corn kernels. We divided the kernels up into four different categories in relation to their appearance: purple and smooth; purple and rough; yellow and smooth; and yellow and rough. We counted the number of corn kernels in each category and recorded the data into our chart.
Soybean Seedlings First, we obtained one hundred soybean seeds and planted them into a flat. We planted them in ten rows with ten seeds per row. We placed the flat in a proper environment for the soybean plans to grow effectively. Within the next two weeks, the soybean seeds developed into a seedling that grew leaves. Next, we began our observation. We counted the number of seedlings in each of the following categories: seedlings with dark green leafs, seedlings with light green leafs, and seedlings with yellow leafs. Once we finished examining the leafs of the soybean plant, we counted the number of seedlings with green cotyledons versus the number of soybean plants with yellow cotyledons. The data was then recorded into a chart so we could further analyze the phenotypes.
Results
Green and Albino Corn Genetics We expected that out of one hundred corn seedlings, seventy-five of them would be the dominant green seedlings. The recessive allele were the albino seeds, expected there to be twenty-five seedlings. The expected ratio was three dominant green seedlings to every one albino seedling.
During our actual observation of the corn seedlings, we found that fourteen of our planted corn seeds did not germinate. Out of the eighty-six corn seeds that did germinate, seventy of them were green seedlings and sixteen of them were albino seedlings. When compiling the data between our expected outcome and our actual outcome, we obtained an X^2 value from our analysis was 1.57 and our P-value was between .20 and .30(Table 1). Therefore, the deviation is not significant and we can accept our hypothesis.
Analysis of a Di-Hybrid Cross in Corn While observing the corn kernels, we counted three hundred and one kernels. Out of the three hundred and one kernels, we expected fifty-six of them to be yellow and smooth; nineteen to be yellow and smooth; one hundred and sixty-nine to be purple and smooth; and fifty-six to be purple and rough. During our actual observation, we found that fifty-two of the kernels were yellow and smooth; nineteen were yellow and rough; one hundred and sixty-three were purple and smooth; and sixty-seven were purple and rough. When compiling the data between our expected outcome and our actual outcome, we obtained an X^2 value of 2.66 and a P-value between .3 and .5(Table 2). Therefore, the deviation was not significant and we can accept our hypothesis.
Soybean Seedlings During our observation, we counted fifty-nine soybean seedlings. We expected fifteen of these seedlings to have dark green leafs, twenty-nine to have light green leafs, and fifteen of them to have yellow leafs. Also, out of the fifty-nine seedlings, we expected forty-four of these to have green cotyledons and fifteen of these to have yellow cotyledons. Our observation revealed that twenty of the seedlings had dark green leafs, twenty-four had light green leafs, and fifteen had yellow leafs. We counted forty-five seedlings with green cotyledons and fourteen with yellow cotyledons. When comparing our expected results with our actual results, we found that we can accept our hypothesis in both the leafs and cotyledons. The leafs had an X^2 value of 2.22, generating a P-value between .3 and .5. (Table 3) The cotyledons had an X^2 value of .09 and a P-value between .5 and .8. (Table 4) Both observations did not have a deviation significant enough to deny our hypothesis.

Discussion After performing the experiments, we were able to draw some conclusions about our hypothesis on genes and inheritance. Our experiments fully supported our hypothesis based off Mendel’s proposed laws of heredity. During our observation of green and albino corn genetics, we expected the phenotypic ratio of the F1 offspring from a cross between two corn plants heterozygous for chlorophyll production to be three dominant green seedlings to every one albino seedling. The genotype between these two corn plants was hypothesized with the usage of a Punnet Square. We expected the genotype to be CC, Cc, Cc, and cc. CC being a dominant homozygous offspring (green), Cc being a dominant heterozygous offspring (green), and cc being a recessive homozygous offspring (albino).
We expected to have seventy-five green and twenty-five albino seedlings out of the one hundred seeds we planted, expecting all one hundred to germinate. Unfortunately, fourteen of our seedlings failed to germinate. Out of the total eighty-six that did germinate we expected an outcome of physical traits to be sixty-five green and twenty-one albino.
During our actual observation, we found that there were more green seedlings than we expected and less albino seedlings than expected, although our predictions were close. One reason as to why we did not observe as many albino seedlings as expected is because there is a ‘genetic survival of the fittest’. Less albino plants will be observed because they do not survive past the seedling stage. The recessive albino plants do not contain the chlorophyll gene necessary to carry out photosynthesis and survive.
Although our expectations differed from our actual observations, we can still accept our hypothesis. We can accept our hypothesis because the deviation between our expected and observed values was not significant. We determined the deviation between these values by using a Chi-Square chart.
Using the Chi-Square test is significant in answering two questions: is our deviation between our observed values and expected values due to chance or other factors, and is our deviation significant enough to deny our hypothesis or not. If the deviation is significant, there must be other factors involved and the hypothesis must be denied. If the deviation is not significant, we can assume that the deviation is due to chance only and we can accept our hypothesis.
In order to duplicate this experiment while using the plants from our flat, we would have to cross-test the different plant seeds. For starters, it is impossible to duplicate the albino plants because they have no seeds. The second problem we run into is that from the naked eye we cannot tell which green seeds are homozygous versus heterozygous. Therefore, we would have to plant the seeds and see whether the seeds germinate into green or albino seedlings. Any seed that germinates into an albino seedling is a heterozygous seed. Throughout this procedure, the different plant seeds will fertilize with themselves. Our goal is to obtain heterozygous seeds to plant in the flat for next semester’s class.
During our observation of a di-hybrid cross in corn, we hypothesized that the F2 generation would produce the following genotypes: SP, Sp, Ps, ps and the following phenotypes: purple, smooth; purple, rough; yellow, smooth; yellow rough. We hypothesized this because we used a Punnet Square to determine the outcome of a di-hybrid cross between two heterozygous parents for both kernel texture and kernel color.
When observing our frequencies in comparison to our expected frequencies, our Chi-Square test revealed that our deviation was not significant. Our X^2 value was 2.66 and our P-Value was between .30 and .50. Therefore, we can accept our hypothesis.
During our observation of the soybean seedlings, we hypothesized to obtain a ratio of 1:2:1. We expected to see one dark green seedling leaf (GG), to every two light green seedling leafs (Gg), to every one yellow green seedling leaf (gg). After comparing our expected results to our observed results using the Chi-Square analysis, our deviation was not significant and we can accept our hypothesis.
The results of the seedling leaf color represents incomplete dominance. One allele did not have complete dominance over another allele for a specific trait. This resulted in an additional phenotype. The physical traits of this third phenotype were made up of both the recessive and dominant physical traits of the parents. (Bailey, 2014) We crossed a dark green soybean plant with a light green soybean plant resulting in our third phenotype: yellow soybean plants.
Our hypothesis on the color of cotyledons of the soybean plants was very close. We were only off by one number on each hypothesized amount. Our P-Value fell between .5 and .8. The deviation was not significant and our hypothesis was accepted. We can assume that our deviation was simply due to chance.
Throughout our experiments on genetic testing, we can conclude that alleles for a certain trait segregate during the formation of gametes. Gametes are formed through meiosis, a type of cell division. During fertilization, the different allele pairs unite. (Bailey, 2014) This explains why we may not see a recessive trait in the first generation and then observe the recessive trait returning in the second generation.
Appendix A

Table 1: Color of Corn Seedlings Observed Versus Expected
(Out of 86 Corn Seedlings, 14 did not germinate) | Green Seedlings | Albino Seedlings | Observed | 70 | 16 | Expected | 65 | 21 |
X^2 Value: 1.57 P-Value: Between .20 and .30

Table 2: Color and Texture of Corn Kernels Observed Versus Expected
(Out of 301 Corn Kernels) | Yellow Smooth | Yellow Rough | Purple Smooth | Purple Rough | Observed | 52 | 19 | 163 | 67 | Expected | 56 | 19 | 169 | 56 |
X^2 Value: 2.66 P-Value: Between .30 and .50

Table 3: Color of Corn Seedling Leafs Observed Versus Expected
(Out of 59 Corn Seedlings) | Dark Green Leafs | Light Green Leafs | Yellow Leafs | Observed | 20 | 24 | 15 | Expected | 15 | 29 | 15 |
X^2 Value: 2.22 P-Value: Between .30 and .50

Table 4: Color of Corn Seedlings’ Cotyledons Observed Versus Expected
(Out of 59 Corn Seedlings) | Green Cotyledons | Yellow Cotyledons | Observed | 45 | 14 | Expected | 44 | 15 |
X^2 Value: .09 P-Value: Between .05 and .08

References
Bailey, Regina. "What Is Incomplete Dominance in Genetics?" About. Web. 12 Nov.
2014.<http://biology.about.com/od/geneticsglossary/g/incompletedom.htm>.
Metzler, K. (n.d.). What is Homozygous? - Definition, Traits & Example | Education
Portal. Retrieved November 12, 2014, from http://education- portal.com/academy/lesson/what-is-homozygous-definition-traits- example.html#lesson