Lab Report: C.elegans Inheritance Experiment

Abstract

In this experiment, we sought to replicate Gregor Mendel's classic investigation of trait inheritance using garden peas. Instead of garden peas, we employed the transparent C.elegans worm as our model organism. The primary objective was to observe the pattern of inheritance for a specific phenotype, namely the dpy-3 gene.

We conducted two separate crosses: one between dpy-3 hermaphrodites and wild-type males and the other involving self-fertilization using the offspring from the initial cross. Through this experiment, we aimed to confirm the recessive and sex-linked nature of the dpy-3 gene.

Introduction

Our experiment aimed to explore the transmission of traits across generations, inspired by Gregor Mendel's groundbreaking research using garden peas. Instead of using garden peas, we employed C.elegans, tiny transparent worms that feed on microorganisms found in decaying fruits and vegetables (1). C.elegans were chosen for this experiment due to their ease of culture and maintenance in a laboratory setting. They can be grown on agar plates with bacteria such as E.

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coli, serving as a food source. Additionally, C.elegans have a short life cycle, taking only 3 to 5 days to develop from an embryo into a sexually mature adult, making them an ideal subject for this study.

Methods

Before commencing the experiment, it was essential to distinguish between the different sexes and phenotypes of C.elegans. Hermaphrodites have a tapered, longer tail with visible female reproductive organs, while males have shorter, blunter tails. We also needed to differentiate between the four distinct phenotypes: wild type (WT), roller (Rol), multivulvae (Muv), and dumpy (dpy).

Wild-type worms are approximately 1mm in length and have a smooth exterior, while roller worms exhibit a twisted circular shape, multivulvae worms display bumps on their exterior, and dumpy worms are short and thick. Once we could distinguish between sexes and phenotypes, we practiced the technique of transferring worms between agar plates until we became proficient.

The actual worm transfer involved placing an agar plate under a dissecting scope and luring C.elegans onto a platinum wire worm pick tool coated with E. coli. Once on the pick, we transferred them to another agar plate.

The first cross included 5 dpy-3 hermaphrodites and an agar plate filled with wild-type-looking males. After transferring the worms into the same agar plate, we wrapped the plates with parafilm and incubated them at 15 degrees Celsius. The second cross involved taking the offspring of the first cross, specifically the L4 hermaphrodites, and allowing them to self-fertilize. The incubation temperature and time remained consistent with the initial cross.

Results

Chi-Square Analysis Of C.elegans

Sum (O) = 1,802

Sum (E) = 1,802

Sum (X^2) Total: 108.5503

Level of Significance: 0.05

Degree of Freedom = 3

X^2 = 108.5503

P value = p ≤ 0.5

Reject or fail to reject hypothesis? Reject

Discussion

There are several reasons for the lower observed percentage of dumpy (dpy) male worms compared to the expected percentage. Firstly, our hypothesis that the dpy-3 gene is recessive appears to be accurate. This recessiveness explains the significant difference between the observed and expected proportions of dpy males. While other phenotypes closely matched their expected percentages, the observed percentage of dpy males was notably lower.

Another contributing factor to the low observed percentage of dpy males is the experimental approach. In the second cross, we selected L4 wild-type hermaphrodites, which already had the dpy-3 gene as a recessive trait. Additionally, according to the C.elegans lab manual, hermaphrodites typically produce progeny that are 99.95% hermaphrodites and only 0.05% males (1). When combined with the recessive nature of the dpy-3 gene, this accounts for the scarcity of dpy male worms.

In conclusion, our experiment confirmed the correctness of our hypothesis that the dpy-3 gene is both recessive and sex-linked. The discrepancy in the percentage of observed dpy males can be attributed to the nature of the gene and the experimental setup.

References

1. Biol.1001 by Rina Shrestha, Catherine McEntee, and Mara Schvarzstein. Brooklyn College, CUNY