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Fly Lab Shannon Ladd

Introduction:

Famers and herders have been selectively breeding their plans and animals to produce more useful hybrids for thousands of years. It was somewhat of a hit or miss process since the actual mechanisms governing inheritance were unknown. Knowledge of these genetic mechanisms finally came as a result of careful laboratory breeding experiments carried out over the last century and a half. A contributing geneticist named Gregor Mendel (1822-1884), discovered through his research the basic underlying principles of heredity that also applied to humans and other animals. Mendel discovered that certain traits show up in offspring without any blending of parent traits. This observation that these parental traits do not show up in offspring plants with intermediate forms was critically important because the leading theory in biology at the time was that inherited traits blend from generation to generation.

He came to three important conclusions from his experiments by which I will conduct through my experiments on fruit flies.

1. The inheritance of each trait is determined by genes

2. An individual inherits one such gene from each parent for each trait

3. A trait may not show up in an individual but can still be passed on to the next generation

It is important to notice that the starting parent plants were homozygous and both parent pea plants had two identical alleles. The plants in F1 generation were all heterozygous with two different alleles, one from each parent. This part can be understood more clearly by looking at the genotypes instead of only the phenotype. Mendel also discovered that one trait is dominant over the other trait. However, the dominant allele does not alter the recessive allele in any way and both alleles can be passed on to the next generation unchanged. These experiments can be summarized as two principles: the principle of segregation and the principle of independent assortment.

1. The principle of segregation: For any particular trait, the pair of alleles of each parent separate and only one allele passes from one parent on to an offspring. Which allele in a parent’s pair of alleles is inherited is a matter of change. This segregation of alleles occurs during the process of sex cell formation.

2. The principle of independent assortment: different pairs of alleles are passes to offspring independently of each other and the result is that new combinations of genes present in either parent are possible. This principle explains why the human inheritance of a particular eye color does not increase or decrease the probability of having 6 fingers on each hand. It is due to the fact that the genes for independently assorted traits are located on different chromosomes.

One of the reasons Mendel carried out his breeding experiments with pea plants was that he could observe inheritance patterns in up to two generation a year. Fruit flies and bacteria are commonly used for this reason now. Fruit flies reproduce in about 2 weeks from birth and bacteria such as Ecoli found in our digestive systems and reproduce in only 3 to 5 hours.

For my experiment, a fruit fly, Drosophila melanogaster will be used. Drosophila has been one of the most well studied mode organisms for learning about genetics and embryo development. These small flies are hardy to grow under lab conditions, and they reproduce easily with a relatively short life cycle of about two weeks; hence, crosses can be performed and offspring counted over reasonable intervals of time. Another advantage of Drosophila is that loci for many genes on the four chromosomes in the fly’s genome have been developed that effect different phenotypes in Drosophila.

Objectives:

The purpose of this lab is to:

1. Simulate basic principles of genetic inheritance based on Mendelian genetics by designing and performing crosses between fruit flies.

2. Understand the relationship between an organism’s genotype and its phenotype.

3. Demonstrate the importance of statistical analysis to accept or reject a hypothesis.

4. Use genetic crosses and recombination data to identify the location of genes on a chromosome by genetic mapping.

General Method:

The fruit fly, Drosophila melanogaster will be given several genetic traits to track at each mating. With Punnett Square, Chi-square analysis will be used to hypothesize and calculate the ratio of phenotypes to of the offspring. The Punnett Square is to display the simulation of basic principles of genetic inheritance based on Mendel’s genetics by performing crosses between fruit flies. The Chi-square analysis will be used to accept or reject my hypothesis for the expected phenotype ratio of the offspring for each cross. For the first 4 mating and the last mating (6th one), sex will be ignored and the 5th mating, sex will be considered.

In this lab, some genetic abbreviations will be used as the following and will include other abbreviations for each cross when necessary.

A wild type: +

Sepia eye Color: SE

Lobe-eyed shape: L

Curved Wing shape: C

Methods, Results and Discussion for each cross

Mating 1: Wild type female and Sepia eye color male

Cross 1: F1

Table 1: Chi Square Hypothesis using cross 1

|Phenotyp|Observed|Hypothes|
|e | |is |
|SE |+SE |+SE |
|SE |+SE |+SE |

From this data, it is shown that when a wild type fly mates with homozygous sepia eyed fly, the resulting offspring only has wild type. This evidence can suggest that wild type is the dominant allele over sepia eye because in order for the offspring to have only wild type from parents that have different homozygous allele, the wild type must be the dominant allele. The Punnett Square show the logic of this conclusion. Genotype of the offspring is +SE and phenotype of the offspring is all wild types.

Cross 2: F2

Table 3: Chi Square Hypothesis using Cross 2

|Phenotyp|Observed|Hypothesis|
|e | | |
|+ |++ |+SE |
|SE |SE+ |SESE |

Data from Table 3 and Table 4 support that the dominant allele for eye is wild type. As suggested from F1 Punnett Square, F1 generation only has a wild type for phenotype with genotype of +SE. When these heterozygotes cross together, they are expected to produce F2 generation with a phenotype ratio of 3:1 for wild type to sepia eye offspring as shown in the Chi Square of Table 1. According to the Chi Square (Table 3), the level of significance is very low since the result is very close to the expected outcome. The genotype ratio of the offspring is ++: +SE: SE = 1:2:1 and the phenotype ratio of the offspring of Wild type to Sepia eye = 3:1.

Mating 2: Lobe-eyed female with wild type male

Cross 1: F1

Table 1: Chi Square Hypothesis using Cross 1

|Phenotyp|Observed|Hypothes|
|e | |is |
|+ |L+ |L+ |
|+ |L+ |L+ |

From this data, it is shown that when a lobe eyed fly mates with homozygous wild type male fly, the resulting offspring only has lobe eyes. This evidence can suggest that lobe eye is the dominant allele over wild type because in order for the offspring to have only lobe eyes from parents that have different homozygous allele, the lobe eyes must be the dominant allele. The Punnett Square shows the logic of this conclusion. Genotype of the offspring is L+ and phenotype of the offspring is all lobe eyes.

Cross 2: F2

Table 3: Chi Square Hypothesis using Cross 2

|Phenotyp|Observed|Hypothes|
|e | |is |
|L |LL |L+ |
|+ |L+ |++ |

Data from Table 3 and Table 4 prove that the dominant allele is lobe eye. As suggested from F1 Punnett Square, F1 generation only has lobe eyes for phenotype with genotype of L+ When these heterozygotes cross together; they are expected to produce F2 generation with a phenotype ratio of 3:1 for lobe eye to wild type eye offspring as shown in the Chi Square of Table 1. According to the Chi Square (Table 4), the level of significance is very low since the result is very closed to the expected outcome. The genotype ratio of the offspring is LL, L+, ++ = 1:2:1 and the phenotype ratio of the offspring of lobe eye to wild type eye is 3:1.

Mating 3: Wild type female with curved wing male

Cross 1: F1

Table 1: Chi Square Hypothesis using Cross 1

|Phenotyp|Observed|Hypothes|
|e | |is |
|+ |+C |+C |
|+ |+C |+C |

From this data, it is shown that when a wild type fly mate with curved wing fly, the resulting offspring only has wild type wing. This evidence can suggest that wild type is the dominant allele over curved wing because in order for the offspring to have only wild type wings from parents that have different homozygous allele, the wild type wing must be the dominant allele. The Punnett square shows the logic of this conclusion. Genotype of the offspring is +C and phenotype of the offspring has all wild type wings.

Cross 2: F2

Table 3: Chi Square Hypothesis using Cross 2

|Phenotyp|Observed|Hypothes|
|e | |is |
|+ |++ |+C |
|C |+C |CC |

Data from both Table 3 and Table 4 support that the dominant allele for wings is wild type and recessive allele is curved wing type. As suggested from F1 Punnett Square, F1 generation only has wild type wings for phenotype with genotype of +C. When these heterozygotes cross together, they are expected to produce F2 generation with a phenotype ratio of 3:1 for wild type wing to curved wing offspring as shown in the Chi Square of Table 1. According to the Chi Square (Table 3), the level of significance is very low with the total of 0.7843 since the result is very closed to the expected outcome. The genotype ratio of the offspring is ++: +C: CC= 1:2:1 and the phenotype ratio of the offspring of wild type wing to curved wing is 3:1.

Mating 4: Sex-linked trait: Tan body female with a wild type male

Cross 1: F1

Table 1: Chi Square Hypothesis using Cross 1

|Phenotyp|Observed |Hypothesis |
|e | | |
|X+ |(X+ XT)+ |(X+ XT )+ |
|Y+ |(Y+XT )T |(Y+ XT )T |

Chi Square test statistics is 0.0290, degree of freedom is 1, and level of significance is 0.8650. The result of data analysis recommends not reject the hypothesis. This means the data is accurate. The dominant allele for the phenotype of the F1 female is wild type body. However, the dominant allele showing for phenotype of F1 male is tan body Table 2 Punnett table shows the phenotype ratio of offspring, 2:2; however, by looking at each pair, all four pairs have different genotype.

Mating 5: Sex-linked trait: Wild type female with tan body male

Cross 1: F1

Table 1: Chi Square Hypothesis using Cross 1

|Phenotyp|Observed |Hypothesis |
|e | | |
|XT |(XX)+ |(X X)+ |
|YT |(YX)+ |(YX)+ |

For this data, Chi Square test statistics is 0.3162, degree of freedom is 1, and level of significance is 0.5739. The result of data analysis recommends not reject the hypothesis. This means the data is accurate. The phenotype from F1 both female and male has wild body as the dominant allele. Table 2 Punnett table shows that wild type body is shown on the appearance of these flies even though by looking at each allele can see that there are four pairs of genotype. The ratio of the phenotype offspring is 2:2.

Mating 6: Dihybrid Cross: Vestigial wings and ebony body color

E = wild type body color e: ebony body color

V: wild type wing size v: vestigial wing size

Cross 1: F1

Female: Ebony body with wild type wing: eV

Male: Vestigial wing size with wild type body color: vE

Table 1: Punnett Square

| |eV |eV |
|vE |EVev |EVev |
|vE |EVev |EVev |

Table 2: Chi Square Hypothesis using Cross 1

|Phenotype |Observed |Hypothesis |Expected |Proportion |
|EV |EEVV |EEVv |EeVV |EeVv |
|Ev |EEVv |EEvv |EeVv |Eevv |
|eV |EeVV |EeVv |eeVV |eeVv |
|ev |EeVv |Eevv |eeVv |eevv |

From cross 2:F2, it further supports that a cross between an ebony body(wild type wing) and vestigial wing (wild type body) is a dihybrid. As suggested in Table 1 Punnett Square from cross 1, the F1 generation only has wild heterozygous type. When these heterozygotes cross together, they are expected to produce F2 generation with a phenotype ratio, 9:3:3:1 for wild body to wild wing to vestigial wig shape to mixture of wild body color and vestigial wing.

The genotype ratio of the offspring is EEVV: EEVv: EeVV: EEVV: EeVv: Eevv: eeVV: eeVv: eevv = 1:2:2:4:1:2:1:2:1 and the phenotype ratio of the offspring is 9 wild body and wing: 3 wild body: 3 wild wing: 1 vestigial wing with ebony body. The dominant phenotype is wild type in both body color and wing size. The recessive phenotype is vestigial with ebony body offspring.

Chi-Squared test statistics is 4.0471 and the degree of freedom is 3. But the level of significance is only 0.2564 and data analysis recommends accept my hypothesis since they are very close to the actual outcome.

Conclusion

I liked doing these fly lab experiments because I was able to play with genes, something I find very interesting myself. Studying the important principles of genetics as well as developing my own hypothesis and creating different traits between fruit flies was a lot of fun. I applied the measures of the statistical test of my data using the Chi-square analysis to see if my hypothesis actually predicted the phenotype ratio of the offspring for each cross. After doing this fly lab, I’ve concluded that it seems very possible to study many different generations of offspring and perform testcrosses. I obtained more evidence and support through my use of the Punnett squares and drawing them for each cross to test backward, and even predicted accurate outcomes. This experiment is very useful and people can learn the simple genetic principles as well as more complex. I enjoyed doing this lab very much.

References

Barbara Pratt (2013), Heredity and Genetics Lecture Note, CCV.edu.
Barbara Pratt (2013), Fly Lab Instructions, Lecture Note, CCV.edu.
Michael Palladino (2001), Student Lab Manual for Biology Labs On-Line, Monmouth University
http://anthro.palomar.edu/mendel/mendel_1.htm

References: Barbara Pratt (2013), Heredity and Genetics Lecture Note, CCV.edu. Barbara Pratt (2013), Fly Lab Instructions, Lecture Note, CCV.edu. Michael Palladino (2001), Student Lab Manual for Biology Labs On-Line, Monmouth University http://anthro.palomar.edu/mendel/mendel_1.htm

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