Throughout thisexperiment we were able to investigate and learn the basic principles ofmonohybrid inheritance by observing Drosophila. Throughput our observations wewere required to record the numbers of flies that displayed mutant traits. Wethen were able to observe the way mutant traits are passed down from onegeneration to the next.
With the data we collected, we were then able toconstruct a hypothesis to describe the mode of inheritance for a mutation.Introduction Drosophila melanogaster,also known as the fruit fly is one of the most commonly used and understoodmodel organisms. Why use Drosophila? There are many different things that makeDrosophila so valuable for the study of genetics and development, some of theseinclude: inexpensive, short reproductive cycle, easy maintenance and storage,full genome was decoded and published in the year of 2000. The fly’s life cycleis completed within about 12 days.
One main difference between males andfemales are the shape and color of the posterior abdomen. Males will havedarker and wider posteriors than the females. Another difference is that maleflies have a sex combs on their upper forelegs while females don’t. What is dominance andrecessiveness? Dominant alleles are shown whenever the individual has one copyof the dominant allele. (Heterozygous) Recessive alleles are shown whenever theindividual has two copies of the same recessive allele. (Homozygous) There isalso a possibility for both alleles to be dominant, each for a different trait,resulting in both alleles being shown equally as much. This is known ascodominance. A monohybrid cross is themating between two different individuals that have different alleles at onespecific locus.
Chi-square analysis is a statistical analysis that is used todetermine whether you should accept or reject your null hypothesis. Accept thenull hypothesis when the deviation can be attributed to chance alone. Rejectthe null hypothesis when the deviation is unable to be attributed to chancealone.The purpose of thisexperiment is to learn about the basic principles of monohybrid inheritance. Iexpected that the experiment would show a 3:1 phenotypic ratio. I expected thisbecause of Mendel’s research of a monohybrid cross that showed a 3:1 phenotypicratio.In the experiment we usedtwo different types of Drosophila, wild type flies (winged) and mutant apterousflies.
(wingless) Materials· One vial of wild-type Drosophila (winged)· One vial of mutant apterous Drosophila(wingless)· Sorting brushes· Microscope· Notecards· FlyNap MethodsWeek1 Part1: Observed and Sexed DrosophilaDuring week 1 we receivedtwo different vials, P1 and P2. One vial containedwild-type Drosophila and the other contained mutant type apterous flies. We thenpracticed the procedure for administering the FlyNap to the flies. This wasimportant for ensuring that our flies wouldn’t die from an overuse of theFlyNap. Once we were comfortable with the procedure we then used the FlyNap oneach vial of flies. We then knocked placed them on notecards and under amicroscope for observation. Comparing the mutants with the wild-type flies.
Wealso sexed the flies. Recording the sex and phenotypes.Part2: Setting up F1 vialsWe then received an emptyvial that we labeled with our group name and description of the cross labeled F1.We moved the anesthetized P1 and P2 flies, includingmales of one phenotype and virgin females for the other into this new F1vial.Week2Part3: Clearing of F1 vialsApproximately a weeklater after the cross has started, we were instructed to remove the parentsfrom the F1 vial using FlyNap and transfer them into the morgue.
This was imperative to ensure there wasn’t any genetic crossover between theparents and the F1 generation.Week3Part4: Setting up F2 vialsDuring week 3 we wereinstructed to use FlyNap on the flies and place them onto a notecard forobservation. We then used brushes to sort and identify the flies phenotype.While also scoring the flies, including the number of males and females thatdisplay wild-type and mutant apterous phenotype.
Then we divided an equalnumber of males and females from the F1 vial into a new vial labeledwith our group’s name and F2.Week4Part5: Clearing F2 vialsDuring week 5, we wereinstructed to remove the F1 adult flies that were previouslytransferred into the F2 vials using FlyNap to prevent any type ofgenerational crossover. We then disposed of these flies into the morgue.Week5Checked on our flies.Week6Part6: Scoring F2 FliesApproximately 10-14 dayslater we were instructed to anesthize the F2 vials using FlyNap andplace them onto a notecard. We then observed the flies underneath themicroscope and sorted them with brushes to score and identify the phenotypes.
Recording the number of males and females that display wild-type and mutantapterous phenotype. Results and DiscussionThe P1 Generationconsisted of a monohybrid cross between wild type and mutant apterous resultingin the F1 generation displaying all wild type. The results for the crossbetween the first and second-generation mating had displayed a 3:1 phenotypicratio. ¾ of the individuals were wild-type and ¼ were apterous. This is becausewild-type phenotype is dominant over the apterous phenotype. We used the methodof true breeding.
This is when an individual is homozygous for every trait forthe P1 generation. Which resulted in a phenotype of 100% wild-type.Concluding that the F1 generation was heterozygous, containing botha dominant and recessive allele. Regarding the resultsfrom Chi-square analysis, we were able to accept the null hypothesis for boththe F2 vials. (top left/bottom left) This means that the deviationscan be attributed to chance alone.
We were also able to accept the nullhypothesis for the F2 vial (top right) and reject the nullhypothesis for the F2 vial. (bottom right) By rejecting the nullhypothesis we are admitting that the deviation can not be attributed to chancealone.Throughout our experimentwe learned about the basic principles of monohybrid inheritance. We crossedboth a wild-type Drosophila with an Apterous Drosophila to explore the way amutant trait is passed down from one generation to the next.
The results forthe P1 generation had went as I had expected. When a dominantwildtype Drosophila (AA) is crossed with a mutant apterous Drosophila (aa), a3:1 ratio is expected. ¾ being wildtype and ¼ being apterous for the F1generation. Regarding the resultsfrom Chi-square analysis, we were able to accept the null hypothesis for boththe F2 vials. (top left/bottom left) This means that the deviationscan be attributed to chance alone. We were also able to accept the nullhypothesis for the F2 vial (top right) and reject the nullhypothesis for the F2 vial.
(bottom right) By rejecting the nullhypothesis we are admitting that the deviation cannot be attributed to chancealone. The reason for rejecting the null hypothesis could have been the resultof a miscalculation or observation of the Drosophila’s phenotypes. Onedifficulty throughout this experiment was keeping the flies from falling intotheir food and getting stuck after anesthizing them with the FlyNap. Anotherdifficulty is that the food would also occasionally fall out of the vial alongwith the flies. I enjoyed being able to observe the way mutations are passeddown from one generation to the next.
Precautions1) When using the FlyNap to anesthetize theflies, make sure to tilt the vial on its side. This will help to prevent anyflies from falling into the food.2) Be careful not to use too much FlyNap toanesthetize the flies.
This may result in the death of the flies.3) When clearing the vials of the adult fliesbe sure to get all of them, if not it will result in generational crossover.4) When dealing with the vials there are manyflies so be sure to avoid any scoring errors and escaping flies.References Education, P.
(2017). ModifiedMastering Genetics with Pearson eText — Standalone Access Card — forEssentials of Genetics, 9th Edition