Lab Report: Drosophila Genetics

Abstract

This lab report explores the life cycle, sex determination, and inheritance patterns of Drosophila, focusing on eye color as a sex-linked trait. Through controlled crosses, we generated F1 and F2 generations, and our results demonstrated Mendelian inheritance patterns, confirming the expected ratios of red-eyed and white-eyed flies. Statistical analysis confirmed a 1:1 sex ratio in the F2 generation, validating the principles of Drosophila genetics.

Introduction

The history of fruit flies is considered a tradition. Research of these flies initially entered labs 100 years ago.

Thomas Hunt Morgan, who lived from 1866 to 1945, was the founder of drosophila genetics. Thomas preformed his research in Morgan lab at the Columbia University in 1910. Here was when they found a famous mutation, know as the white-eyed fly. Quite an accomplishment was this discovery, but the end of the 1980's there were 3,000+-recorded mutations. Now drosophila is very popular; so popular, it would be almost impossible to list the number of things that are being done with it.

Get quality help now

Writer Lyla

Verified writer

Proficient in: Biology

5 (876)

“ Have been using her for a while and please believe when I tell you, she never fail. Thanks Writer Lyla you are indeed awesome ”

+84 relevant experts are online

Hire writer

However, fruit-fly research relates to human genetics as well. It conveys that genes were related to proteins, therefore referring to the study the rules of genetic inheritance. Currently, it is used mostly in biology, focusing on how a complex organism matures from a fairly simple fertilized egg (embryonic development).

Aside from the fact that drosophila can be found throughout numerous biology labs, they don't originate in these labs. Drosophila is found all around the world, more species in the tropical regions; whether it is deserts, tropical rainforests, cities, swamps, or alpine zones.

More often than not they are found living in habitats that have fermenting or rotting vegetation, caused by various yeasts and bacteria. Breeding environments consist of varies between decaying fruits, plant material, mushrooms, slime fluxes, flowers, etc. These breeding environments initiate the life cycle of the next drosophila generation. Just like humans female fruit flies produce eggs and males produce sperm. When the egg and sperm join, the egg becomes fertilized and starts to develop. In fruit flies, sperm is deposited from the male fruit fly into the female fruit fly, enabling the female to store sperm inside of her. The eggs are fertilized when they pass through the oviduct on their way to being placed in a food source. Fruit flies begin their lives as an embryo in an egg. This stage lasts for about one day.

During this time, the embryo develops into a larva. The first instar larva hatches out of the egg, crawls into a food source, and eats. The larva in each stage eats as much as possible. After a day, the first instar larva transforms and becomes the second instar larva. Again, the larva in this stage eats. After two days in this stage, the larva transforms again to become the third instar larva. After three days of eating in this stage, the larva crawls out of the food source and transforms again. Following this transformation, the larva stops moving and forms a pupa. Drosophila stays in the pupa for about five days. During this time, the metamorphosis, from larva to adult is occurring. Adult characteristics, like wings, legs, and eyes develop. When the adults emerge from the pupa, they are fully matured. They gain reproductive attributes after about 15 hours. Soon they breed then the females lay eggs, and the cycle begins again. The whole life cycle takes about 12-14 days.

While focusing on the topic of reproduction and breeding, sex determination and how it works in drosophila is a sensible topic. We being humans, makes it easier to elucidate what sex determination in drosophila is, because both of us are complex organisms. In an easier perspective, sex determination in humans and drosophila are the same. To make sex determination more comprehensible though, I will explain how it occurs in humans. In humans the diploid number of chromosomes is 46 (23 pairs). There are 22 pairs of homologous chromosomes called autosomes. Homologous autosomes look alike. The 23rd pair of chromosomes differs in males and females.

These two chromosomes, which determine the sex of an individual, are called sex chromosomes and are indicated by the letter X and Y. If you are female, your 23rd pair of chromosomes are homologous, XX. However, if you are male, your 23rd pair of chromosomes, XY, looks different. Males usually have one X and one Y chromosome and produce two kinds of gametes, X and Y. Females usually have two X chromosomes and produce only X gametes. It is the male gamete that determines the sex of the offspring. After fertilization, a 1:1 ratio of males to females is expected. Because the laws of probability govern fertilization, the ratio usually is not exactly 1:1 in a small population.

Materials and Methods

Materials

• Drosophila (fruit flies)
• Crossing vials
• Wild virgin females
• White-eyed males
• Incubator

Experimental Procedure

1. For the P1 generation, two wild virgin females (XRXR) and two white-eyed males (XrY) were selected.
2. The F1 generation was created by allowing the P1 flies to mate.
3. Data for the number of Drosophila in the F1 vial was collected on multiple dates (Feb. 16, Feb. 17, Feb. 21, and Feb. 25).
4. For the F2 generation, two females (XRXr) and two males (XRY) were chosen from the F1 generation.
5. Data for the number of Drosophila in the F2 vial was collected on multiple dates (March 6, March 8, March 10, and March 13).

Results

The results of the experiment are summarized below for both the F1 and F2 generations:

F1 Generation

F2 Generation

Discussion

The results of our Drosophila genetics experiment confirm the principles of Mendelian inheritance. In the F1 generation, as expected, all offspring exhibited wild-type (red-eyed) phenotypes. This is consistent with the dominant nature of the red eye allele (XR) over the recessive white eye allele (Xr). However, in the F2 generation, we observed the segregation of traits according to Mendel's laws. We obtained a 3:1 ratio of red-eyed to white-eyed flies in the F2 males, which is indicative of a monohybrid cross involving a dominant and recessive trait.

Furthermore, our statistical analysis of the F2 generation data using the Chi-square (X2) test confirmed a 1:1 sex ratio, which aligns with the expected outcome of fertilization. These results support the established principles of Drosophila genetics, specifically the inheritance of eye color as a sex-linked trait. The sex-linked nature of the eye color gene is evident from the observed phenotypes and ratios.

Thomas Hunt Morgan's pioneering work on Drosophila genetics led to the discovery of sex-linked traits and provided crucial insights into the role of genes located on the X and Y chromosomes. Our experiment reaffirms these principles and highlights the significance of using Drosophila as a model organism for genetic research.

Conclusion

This Drosophila genetics experiment demonstrated the inheritance patterns of eye color as a sex-linked trait, reaffirming the principles established by Thomas Hunt Morgan in the early 20th century. The F1 generation exhibited all wild-type (red-eyed) phenotypes, consistent with the dominance of the red eye allele. In the F2 generation, we observed Mendelian segregation, resulting in a 3:1 ratio of red-eyed to white-eyed flies among males.

Our statistical analysis of the F2 generation data confirmed a 1:1 sex ratio, validating the principles of sex determination in Drosophila. These results emphasize the importance of Drosophila as a model organism for genetic research and its contributions to our understanding of inheritance patterns and sex-linked traits.

Recommendations

Based on the success of this experiment, it is recommended to explore additional genetic traits and inheritance patterns in Drosophila. Further investigations could delve into the interactions of multiple genes, gene mapping, and the effects of environmental factors on gene expression in fruit flies. Additionally, using molecular techniques to examine the underlying genetic mechanisms of sex determination and sex-linked traits in Drosophila would provide valuable insights into the molecular genetics of this model organism.