Sex Linkage In Drosophila Melanogaster Biology Essay

The rules regulating heredity were foremost formulated by Gregor Mendel, who stated that allele braces separate independently from parents to off springs in his rule of independent mixture. Subsequently on, Thomas Hunt Morgan proposed that cistrons were responsible for traits of beings and he used the fruit fly ( Drosophila melanogaster ) in his experiments to analyze the function of cistrons in biological procedures. This Experiment was performed to demo that traits occur as a consequence of heritage due to separation or segregation of alleles/genes. The experiment was aimed at transfusing familial accomplishments in order to guarantee that persons are able to distinguish male from female flies, place common mutant phenotypes, set up familial crosses utilizing being ‘s genotypes and understand how to use informations from familial crosses. Familial crosses were carried out in the lab to exemplify the difference in the heritage forms of sex linked traits. It was observed that the white allelomorph ‘s frequence is higher in males than in females even when mutual crosses are done. This is because this cistron is linked to the X-chromosome.


Fruit flies are widely used in genetic sciences experiments due to their short life rhythm, they multiply in copiousness from merely a individual cross, the cost of keeping the fly is low, handiness of 1000s of mutant and their surveies are easy to execute. Thomas Hunt Morgan worked extensively with these flies and shadow much visible radiation on genetic sciences as it is today. During his experiments, he discovered that the cistron for white eyes in males was entirely inherited with the X-chromosome ( Christiansen 143 ) . This experiment non merely initiated the survey of sex linked traits, but besides provided grounds of the chromosomal theory of heritage. Sexual activity linkage is a signifier of alternate heritage form where by a specific cistron is found on ( X or Y chromosomes ) sex chromosomes. Sexual activity linked traits occur chiefly in males since they merely have one X-chromosome but in females they occur merely when they are homozygous recessionary ( Roberts 453 ) . Sexual activity Linkage falls in a wide categorization of familial linkage where by different allelomorphs are inherited together. This chiefly happens when the cistron loci happening in the same chromosome are physically closer hence do non segregate during miosis, but remain together.

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The white-eyed trait was used in this experiment to demo the heritage of X linked traits. The principle of this experiment is to be able to distinguish male from female flies, be able to place common mutant phenotypes such as oculus colour, form and organic structure colour, set up familial crosses and understand how to use informations from familial crosses ( Christiansen 143 ) . This experiment will besides guarantee that one is in a place to bring forth punned squares for sex linked traits, know the result of certain sex linked traits, be able to utilize these consequences to cipher the figure of persons from the ascertained population in this instance utilizing fruit fly mutual crosses monitor the figure of phenotypes with respect to sex and oculus colour. The two allelomorphs for oculus colour which are used in this experiment are white ( tungsten ) and wild type ( w+ ) , the wild type allelomorph produces ruddy oculus colour and is normally dominant to the white allelomorph ( Kotpal 70 ) .


Experiment 1:

Canton-S females and males flies were anesthetized by CO2 and dumped onto CO2 tablets. The CO2 tablet was them placed under a dissecting microscope and magnified suitably. Differences and features of males and females were observed suitably. A phial of Y tungsten tin three-base hit mutant flies was besides prepared merely like Canton-S. These were observed to place and distinguish between the mutant phenotypes for oculus colour, organic structure colour, and bristle form. These features were compared with the wildtype phenotypes for each feature.

Experiment 2:

Three white eyed males ( hemizygous for the white oculus colour allelomorph ) were anaesthetized and placed in a new phial. In this new phial, three wildtype virgin females ( homozygous for the wildtype red oculus colour allelomorph ) were anaesthetized and introduced and the phial labeled suitably. A mutual cross was so made for the same and labeled. After one hebdomad, the parents were removed from their several phials and dumped into a mortuary ; the larvae were left to turn. After another hebdomad, the phials were retrieved for observation. This was done by anesthetizing the flies and puting them in a Petri dish on top of an ice block. These were so counted to under magnification to place the males and females every bit good as white eyed versus ruddy eyed. Three female and three males were obtained and topographic point in a new phial. A punnet square was performed to foretell the consequences.


Experiment 1: The ascertained features were drawn carefully.

Experiment 2:

From the experiment of the parental cross, the consequences of the first filial coevals ( F1 ) were as follows.

The parental cross is between Xw+ Xw+ females and Xw Y males ( wild type females vs. white males )




White Males: 0 % Red eyed males: 50 %

White Females: 0 % Red eyed Females: 50 %

The parental cross is between Xw+ Xw females and Xw+ Y males ( the F2 coevals )




White eyed Males: 25 % Red eyed Males: 25 %

White eyed Females: 0 % Red eyed Females: 50 %

The mutual cross ( wildtype males Vs. white virgin female flies )




White Males: 50 % Red eyed males: 0 %

White Females: 0 % Red eyed Females: 50 %

The F1 crosses




White Males: 25 % Red eyed males: 25 %

White Females: 25 % Red eyed Females: 25 %


Based on the ascertained features, the males are larger than females and have shorter and rounder wings. The venters of the female is rounded and has striped visual aspect while that of the male is non rounded and is dark ( Roberts 452 ) . The two have different genital organs seeable on the posterior ventral venters ; the female genital organ holding a little gap that forms a smooth point at the terminal of the venters while that of the male consists of more complex cuticular constructions. Males have sex combs ; these are little spots of hair on the cubituss while female do non hold these.

Interesting frequences are observed in the 2nd experiment where by the parental cross wholly differ from the mutual cross. In the original crosses ‘ F2 coevals the consequences are as follows ; White eyed Males: 25 % , Red eyed Males: 25 % , White eyed Females: 0 % , Red eyed Females: 50 % . This is wholly different from the reciprocals ‘ crosses which yield 25 % of each trait. Given these consequences, males are affected by the white oculus mutant to a more extent than the females ( Jeffreys and Wilson 11 ) . This translates to typical sex linkage familial crosses. Since males are hemizygous for this trait, it is expressed even if they have one transcript of the cistron. The females on the other manus must inherit two cistrons for the trait in inquiry because they merely express it when in homozygous province. This means that the trait will be less frequent in the population as compared to the male ‘s frequence.

Work Cited

Christiansen, Freddy, B. Theories of population fluctuation in cistrons and genomes. New Jersey: Princeton University Press, 2008.

Griffiths, A. J. F, Miller, J. H. , Suzuki, D. T. , Lewontin, R. C. , Gelbart, W. M. An Introduction to Genetic Analysis. New York: W.H. Freeman and Company. 1993.

Jeffreys, A.J. , Wilson, Thein, S.L. ( 1986 ) .DNA ” fingerprints ” and segregation analysis of

Kotpal, Tyagi, Dr. Bendre, & A ; Dr. Pande. Concepts of Biology XII. New Dheli: Rastogi Publications.

Morgan, Thomas H. The physical footing of heredity. Philadelphia: Lippincott Company. 1919.

multiple markers in human lineages. American Journal of Human Genetics. 39 ( 1 ) :11.

Roberts, M. B. V. Biology: a Functional Approach. Cheltenham: Nelson Thornes, 1986.


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