Lab Report - Inheritance in Drosophila Melanogaster

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Introduction

Inheritance, as defined by Gregor Mendel, is the process by which traits are transmitted from one generation to another through genetic codes (BasicBiology, 2018). Mendel's studies introduced the concepts of monohybrid and dihybrid crosses in genetics. A monohybrid cross involves individuals that possess varying alleles for a specific gene, with each individual having two dominant and two recessive alleles, respectively (Texas Getaway, 2019). Conversely, a dihybrid cross is conducted between individuals exhibiting two different characteristics, each controlled by a different gene (Scitable, 2014).

Drosophila melanogaster, commonly known as the fruit fly, possesses four sets of chromosomes, among which the X and Y chromosomes determine the fly's sex.

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Females have two X chromosomes, while males have one X and one Y chromosome. Typically, the X chromosome carries most of the genes, with the Y chromosome housing fewer functional alleles, except for genes related to male fertility (Course Hero, 2019).

In this experiment, we utilized coin tosses to determine the genotypes of offspring and calculated the actual phenotypic ratios to compare them with the expected ratios.

Aim

The aim of this experiment was to investigate the inheritance patterns of specific genes and alleles in Drosophila melanogaster flies by conducting monohybrid and dihybrid crosses.

Hypothesis

If different genotypes are crossed together, then offspring with varying genotypes will be produced.

Materials and Procedure

Please refer to the practical handout titled "Investigating Patterns of Inheritance" for detailed information on the materials and procedures used in this experiment.

Results

Part A

Parental Cross: Wild type (tan) body × black body

F₁ Cross: Wild type body (heterozygous) female × Wild type body (heterozygous) male

Expected F₂ Genotypic Ratio: 1 BB : 2 Bb : 1 bb

Expected F₂ Phenotypic Ratio: 3 wild type (tan) body : 1 black body

Genotype	Number of Offspring (Group Data)
BB	12
Bb	19
bb	9
Total	40

Table 1: Group results for F₂ genotypes

Actual F₂ Genotypic Ratio: 12 BB : 19 Bb : 9 bb

Phenotypic Ratio (Group Data):

Phenotype	Number of Offspring	Proportion of Offspring	Ratio
Tan bodies	31	31/40 = 0.78	1.0
Black Bodies	9	9/40 = 0.23	0.30
Total	40

Actual F₂ Phenotypic Ratio: 10 wild type (tan) body : 3 black body

From Pooled Class Data:

Actual F₂ Genotypic Ratio: 95 BB : 191 Bb : 84 bb

Phenotypic Ratio (Pooled Data):

Phenotype	Number of Offspring	Proportion of Offspring	Ratio
Tan bodies	286	283/370 = 0.77	1.0
Black Bodies	84	84/370 = 0.23	0.30
Total	370

Actual F₂ Phenotypic Ratio: 10 wild type (tan) body : 3 black body

Part B

Data Set Number: 4

Parental Cross: True-breeding lobe-eyed fly (EE) × True-breeding wild type fly with normal red eyes (ee)

Let "E" signify the allele of lobe-eye.

F₁ Monohybrid Cross

Female Parent Phenotype: Lobe eyes

Male Parent Phenotype: Lobe eyes

F₂ Offspring:

No wild type females: 122
No wild type males: 130
No lobe-eyed females: 386
No lobe-eyed males: 371

Phenotypic Ratio (Pooled Class Data)

Phenotype	Number of Offspring	Proportion of Offspring	Ratio
Lobe-eyed	252	252/1009 = 0.25	0.3
Wild type	757	757/1009 = 0.75	1.0
Total	1009

Actual F₂ Phenotypic Ratio: 10 wild type : 3 lobe-eyed

Is the Mutated Allele Dominant or Recessive? The mutated allele is dominant because all the offspring in the F₁ generation have lobe eyes, and the majority of offspring in the F₂ generation also exhibit lobe eyes in both females and males.

Is the Investigated Gene Located on an Autosome or X Chromosome? The investigated gene is located on an autosome because it does not determine the sex of the flies.

Part C

Parental Cross: Black body, wild type (red) eye color × Wild type (tan) body color, brown eyes

F₁ Cross: Wild type body color and eyes (heterozygous) female × Wild type body color and eyes (heterozygous) male

Expected F₂ Genotypic Ratio: 1 BBEE : 2 BBEe : 4 BbEe : 2 BbEE : 1 BBee : 2 Bbee : 1 bbee : 2 bbEe : 1 bbEE

Expected F₂ Phenotypic Ratio: 9 wild type (tan) body with (red) eye : 3 tan body with brown eye : 3 black body with red eye : 1 black body with brown eye

Genotype	Number of Offspring (Group Data)
bb EE	4
bb Ee	2
bb ee	2
Bb EE	6
Bb Ee	10
Bb ee	5
BB EE	3
BB Ee	6
BB ee	2
Total	40

Actual F₂ Genotypic Ratio: 4 bbEE : 2 bbEe : 2 bbee : 6 BbEE : 10 BbEe : 5 Bbee : 3 BBEE : 6 BBEe : 2 BBee

Phenotypic Ratio (Group Data)

Phenotype	Number of Offspring	Proportion of Offspring	Ratio
Tan bodies, red eyes	25	25/40 = 0.63	1.0
Tan bodies, brown eyes	7	7/40 = 0.18	0.3
Black bodies, red eyes	6	6/40 = 0.15	0.2
Black bodies, brown eyes	2	2/40 = 0.05	0.08
Total	40

Actual F₂ Phenotypic Ratio: 10 tan body, red eye : 3 tan body, brown eye : 2 black body, red eye : 1 black body, brown eye

From Pooled Class Data:

Actual F₂ Genotypic Ratio: 28 bbEE : 43 bbEe : 28 bbee : 43 BbEE : 87 BbEe : 48 Bbee : 23 BBEE : 44 BBEe : 26 BBee

Phenotypic Ratio (Pooled Class Data)

Phenotype	Number of Offspring	Proportion of Offspring	Ratio
Tan body, red eye	197	197/370 = 0.53	1.0
Tan body, brown eye	74	74/370 = 0.20	0.38
Black body, red eye	71	71/370 = 0.19	0.36
Black body, brown eye	28	28/370 = 0.08	0.15
Total	370

Actual F₂ Phenotypic Ratio: 10 tan body, red eye : 4 tan body, brown eye : 4 black body, red eye : 2 black body, brown eye

Part D

Data Set Number: 4

Parental Cross: True-breeding wild type fly with normal wings and red eyes (BbEe) × True-breeding brown-eyed fly with curled wings (bbee)

F₁ Dihybrid Cross

Female Parent Phenotype: Wild type

Genotype: BbEe

Male Parent Phenotype: Brown-eyed with curled wings

Genotype: bbee

F₂ Offspring:

No wild type offspring: 244
No curled-winged with red eyes offspring: 261
No brown-eyed with normal wings offspring: 259
No brown-eyed with curled wings offspring: 253

Phenotypic Ratio (Pooled Class Data)

Phenotype	Number of Offspring	Proportion of Offspring	Ratio
Wild type (red eyes, normal wings)	244	244/1017 = 0.24	0.92
Brown-eyed with normal wings	259	259/1017 = 0.25	0.96
Red eyes with curled wings	261	261/1017 = 0.26	1.0
Brown-eyed with curled wings	253	253/1017 = 0.25	0.96
Total	1017

Actual F₂ Phenotypic Ratio: 1 wild type (normal wings with red eyes) : 1 normal wings with brown eyes : 1 curled wings with red eyes : 1 curled wings with brown eyes

Are the Mutated Alleles Dominant or Recessive? The mutated alleles are recessive because all the offspring in the F₁ generation have red eyes with normal wings (wild type), indicating that the wild type allele is dominant, clearly expressing the dominant trait.

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In the presence of a dominant allele, the trait of a recessive allele will be masked and can only be observed when the dominant allele is absent.

Are the Investigated Genes Independent? Two genes are independent because the actual F₂ phenotypic ratio precisely matches the expected F₂ phenotypic ratio.

Summary

Part A

Analysis and Discussion:

Wild type is a gene or strain that forms among the species in natural conditions, separate from an atypical mutant type (Study.com, 2019).
Wild type (tan) body color is dominant, indicated by the capital letter "B" used to describe it. The actual phenotypic ratio in both group and pooled class data supports that tan body color is the dominant allele, as it determines the majority of offspring traits.
The trait is autosomal dominant, as all F₁ offspring have lobe eyes, and the majority of F₂ offspring also exhibit this trait. This suggests that the mutated allele is the dominant one, expressing the offspring's characteristics.
Linked genes are genes that are inherited together when they are physically close to each other on the same chromosome (Khan Academy, 2019).
In Part C, the two genes are not linked, as the actual F₂ phenotypic ratio matches the expected F₂ phenotypic ratio for both pooled class and group data, which is 9:3:3:1.
This is a dihybrid cross, providing phenotypic and genotypic ratios for the F₂ generation.
No, they are not linked, as the actual phenotypic ratio matches the expected phenotypic ratio of 1:1:1:1.

Punnett Square

    BE   Be
    be   BbEe   Bbee   bbEe   bbee

The actual F₂ phenotypic ratio in Part A did not match the expected ratio for both group and pooled class data.
One modification is to standardize the coin-tossing method across all groups to minimize variability in results. Additionally, increasing the offspring sample size to 400 can provide more consistent and accurate results (NCBI, 2000).
An extension to this experiment is to use Hardy-Weinberg formulas to determine genetic variation in a population of D. melanogaster at equilibrium, employing the formulas: p + q = 1 and p² + 2pq + q². The Chi-squared test can also be employed to determine if there is a significant difference between the expected and actual results (Course Hero, 2019). The test formula is (O - E)²/E, and the null hypothesis cannot be accepted if the p-value is > 0.05.

Conclusion

Based on the results obtained in Part A and Part C, the observed outcomes did not match the expected ratios. In Part A, both the genotypic and phenotypic ratios deviated from the expected 1BB:2Bb:1bb and 3 wild type:1 black body ratios, respectively. Similarly, in Part C, the genotypic and phenotypic ratios should have been 1 BBEE: 2 BBEe: 4 BbEe: 2 BbEE: 1 BBee: 2 Bbee: 1 bbee: 2 bbEe: 1 bbEE and 9 wild type (tan) body with (red) eyes: 3 tan body with brown eyes: 3 black body with red eyes: 1 black body with brown eyes.

As a result, it can be concluded that the pattern of inheritance cannot be predicted with 100% accuracy, as demonstrated in this experiment.

Lab Report - Inheritance in Drosophila Melanogaster. (2024, Jan 23). Retrieved from https://studymoose.com/document/lab-report-inheritance-in-drosophila-melanogaster