The purpose of this experiment was to determine the F1 genotype of fruit fly traits using the phenotypic ratio of the F2 generation and to express these results of the unknown cross through a Chi-square model and Mendelian genetics. After the experiment, it was found that the parents held a heterozygous genotype through using the Chi-square model, and that the observed and expected values fall within the Chi-squared value which also falls into the p-value. The Chi-squared value was 5. 64, the degrees of freedom was 3 and the p-value was between . 05 and . , which supports the failing to reject the null hypothesis.
The results also yielded the expected 9:3:3:1 ratio showing how different alleles combine and which ones are most prevalent. Using this information, it is concluded that parents hold a dominant and recessive trait for every gene in their genome to survive natural selection. Introduction This lab followed the tract of Mendelian genetics. Gregor Mendel, an Austrian monk, discovered how characteristics such as flower color was carried onto future generations. In Mendelian genetics, the “generations” refer to the offspring of the parent organism.
Regarding generations (for example), an individual’s grandparents are the P generation, and the same individual’s parents are the F1 generation, as in the first set of offspring from the grandparents. That makes the individual the F2 generation. Mendel further went on to prove that parenting figures were carried onto their children, even when not physically expressed (Olby). Gregor Mendel explored the characteristics that every living thing possesses. Whether it be hair color, skin color, or organ development, every living being has a specific code for each trait within their DNA.
These traits are coded by proteins, and the codes for these proteins are found on a physical point on a chromosome called a gene. In sexual reproduction, the alleles for a gene cross and the parent generation (P generation) make offspring that either exhibit, carry, or do not carry the traits that the parents had (Chenoweth & McGuigan). This beauty of reproduction results in genetic variance throughout the world, allowing humanity to survive natural selection. During cell meiosis, the genes undergo a process called crossing over.
Crossing over is when the homologous chromosomes intertwine at the chiasmata and trade places, causing for a new, unique chromosome that is different from the parent cell (Chenoweth & McGuigan). To see crossing over in action, fruit flies under the characterization of Drosophila melanogaster are perfect candidates to use to test genetic traits because of their large reproductive capacity, short generation time, and its relation to human DNA – 61% of human diseases have been found in fruit flies (Nichols & Pandey). Also, Drosophila melanogaster tend to mutate in rapid proportions, making this experiment easier to observe.
Punnett Squares are used to clearly show the phenotypic and genotypic ratios of certain traits in able to predict the next generation (Merriam-Webster). In the Punnett Square below, AB stands for Red Eyes/Normal Wings, Ab stands for Red Eyes/Mutated wings, aB stands for Black eyes/normal wings, and ab stands for black eyes/mutated wings. Gametes AB Ab aB ab AB AABB AABb AaBB AaBb Ab AABb AAbb AaBb Aabb aB AaBB AaBb aaBB aaBb ab AaBb Aabb aaBb aabb The Punnett square above shows the phenotypic and genotypic ratios in the F2 generation are peculiar because the F2 generation does not have an even distribution of traits.
This experiment will be to determine the genotypes and phenotypes of the fruit fly Drosophila melanogaster using an unknown cross and Chi-square model. In biology, Chi-squared models are accurate in deciding the probability of an occurrence to happen. Using the Chi-squared model, it is possible to analyze the strange ratios in the Punnett square and build an experiment to test the probability of this ratio happening. The null hypothesis states that the observed results of the cross do not deviate significantly from the expected results of the cross and follow Mendelian inheritance.
This null hypothesis reflects what the test is because it will be able to decide whether or not Mendelian genetics applies to all lengths of science. Materials and Methods For this two-week lab, Drosophila melanogaster fruit flies were picked based on the phenotypic characteristics of eye color (white or red), and wing formation (normal or vestigial) Red eyes and normal wings were the dominant traits, whereas black eyes and vestigial wings were the recessive traits. The P generation of Drosophila melanogaster were placed inside yeast-fermented cultured tubes and left for a week.
After a week, the sex-linked cross culture tube that was previously prepared was taken and a FlyNap wand was inserted into the tube and was laid horizontally on the table to put the flies into a deep sleep. The wand was then removed and the flies were placed on a white card under a dissecting scope with labels for the respective phenotypes for the flies. The phenotypes were Red eyes/normal wings, Black eyes/normal wings, Red eyes/mutated wings, and Black eyes/mutated wings. Then the fly’s eye color and wing development were recorded into a class data table.
After the collection of data, the flies were placed back into the culture tube as they started to wake up, and the area was cleaned. Microsoft Excel was used to generate tables and Chi-Squared Values for the lab. The P-value cutoff was . 05. Results The lab results were Gathered in a Chi-squared data. See Figure 1. Chi-squared table for unknown Drosophila cross Phenotype Red Eyes/Normal Wings Black Eyes/ Normal Wings Red Eyes/Vestigial Wings Black Eyes/Vestigial Wings Row Total Observed 163 64 43 13 283 Expected 159 53 55 18 283 (Observed-Expected) (O-E) 4 11 -10 -5 NA Observed-Expected) ^2 (O-E) ^2 16 121 100 25 NA (Observed-Expected) ^2 / Expected. (O-E) ^2/E . 100 2. 28 1. 82 1. 39 Chi-Square value: 5. 64 P-value cutoff: 0. 05 P-value: (. 05<0. 2).
The ratio for Red eyes/Normal wings was much greater than the rest of the phenotypic traits. The ratio for Black eyes/Normal wings and Red eyes/Mutated wings were rather close together, following the 3:3 ratio made by Gregor Mendel. The ratio of Black eyes/mutated wings was the smallest ratio recorded, so black eyes/mutated wings would have the :1 ratio in respect to the other data.
Discussion When this experiment was over, the data received by the class revealed that the second generation Drosophila melanogaster parents crossed were heterozygous. Looking at all of the fruit flies, there is no possible way for the parent flies to be homozygous. If the parent flies were homozygous, both the F1 and the F2 phenotypes would be the same holding a 1:1ratio, instead of the 9:3:3:1 ratio that was observed. The purpose of this experiment was to determine the F1 genotype of fruit fly traits using the phenotypic ratio of the F2 generation and to express these results of the unknown cross through a Chi-square model.
After taking data with the Chi-squared value of 5. 64, the degrees of freedom were 3 and the p-value was between . 05 and . 2, it is confident to fail to reject the null hypothesis, which leads the experimenters to believe that the observed phenotypic ratio does significantly deviate from that expected under the assumption of Mendelian inheritance. In the future, exploring more complex animals other than fruit flies, such as mammals or reptiles, would make this experiment a little more difficult, but more interesting as well. Without Mendelian genetics, it would be much more difficult to predict traits in organisms across the living spectrum.
