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Heidi At Stathi

Fly Lab Report

Professor Flynn

I. TitleObserving patterns of inheritance in fruit flies

Heidi Atstathi, Leigh-Ann Wasneechak, Jhazmin Griffith, Lutfur Nahar

II.AbstractThe experimental design discussed throughout this report was devised to further

investigate and observe the patterns of inheritance in three generations of Drosophila

melanogaster, commonly known as fruit flies. The aspect of inheritance under study is that of a

single trait, eye color . The experiment features a monohybrid cross, where true-breeding parent

flies , a red-eyed male and white-eyed female, mate. The procedure then follows with a second

cross between the first generation (F1) of offspring in order to observe the pattern of inheritance

of eye color in the second (F2) generation of offspring. After the completion of successful

breeding across all levels, a chi-square analysis is conducted to evaluate the goodness of fit of

the experimental results and to test whether or not the hypothesis was accurate. The

hypothesis was not supported by the experiment as the eye color gene was sex linked.

III. IntroductionThe experiment is designed to study the pattern of inheritance by studying one trait in

a monohybrid cross. In the experiment eye color of true-breeding fruit flies, red eyed males

and white eyed females, were crossed to observe the inherited eye colors of F2 offspring

generation. At the sight of F1 larvae the parent generation flies are removed to allow

matings to occur among F1 flies. Data was collected for the phenotypic eye color ratios of F2

flies to study the inheritance of the dominant eye color alleles through two generations of

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flies. It was hypothesized that, if true-breeding flies are crossed then the F2

generation should be in a ratio of 3:1, demonstrating a dominant allele.

IV.MethodWeek One: Obtain a small plastic cup that can be fitted with a stopper. Into the plastic

cup pour equal parts Drosphila medium and tap water. Onto medium solution, place 7

grains of yeast. Stopper close the medium. Before the flies are able to be placed into the

solution they must be anesthetized in ice enough for them to be stilled for transfer. Place

three red eyed males and three virgin whited eyed females into the cup, stopper close,

date and label cup.

Week Two: Retrieve the cup of flies, anesthetize flies. Pour out dead adult flies,leaving

behind F1 larvae, the stopper cup closer.Week Three: Retrieve the cup of flies, anesthetize flies, note uniform eye color of F1

flies. Separate three males and three females into fresh vial with freshly prepared medium.

Throw away old vial.

Week Four: Anesthetize flies, pour out dead adult flies leaving behind F2 larvae, stopper

cup.

Week Five: Anesthetize flies long enough to kill them. Observe and count number

of each phenotype. Record and observe date.

V.ResultsThe experiment demonstrated the pattern of inheritance in fly eye color. By

crossing two true-breeding flies, inheritance of alleles was able to be observed

through phenotypic expression. Having a parent generation of true-breeding red

eyed males and true-breeding white eyed females, the monohybrid cross resulted in an F1

generation of heterozygous offspring. The crossing of the F1 generation did not provide

the expected results of a 3:1 ratio, the chi-square test demonstrated that the eye color was a

sex linked trait and gave unexpected results.

Monohybrid Cross- White Eyed Female x Red Eyed Male

R R

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R R

W RW RW

W RW RW

F1 Cross RW xRW (expected) 3:1

R W

R RR RW

W RW WW

Chi-Square Analysis of F2 Phenotypes from Monohybrid Cross

Phenotype Observed(o)

Expected(e)

o-e (o-e)^2 (o-e)^2 /2

Red Eyes 55 51 4 16 0.31

White Eyes 13 17 -4 16 0.94

sum of all observed = 68 sum of X^2 = 1.25

70% sure, not strong. Does not support hypothesis, due to sex linked alleles. Does notsupport 3:1 ratio.

VI. ConclusionBased on these experimental results, it is suggested that the allele for eye color is indeed

sex linked. Furthermore, analysis of the phenotypic expression of eye color and its association to

sex depicts that the results did not support the hypothesis stating a 3:1 ratio of red eyes to white

eyes in the presumed F2 generation of flies.