Title: Sex-Linked Eye Color in Drosophila

Design

Introduction: Sex linked genes is the phenotypic expression of an allele that is related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal chromosomes, where both sexes have the same probability of expressing the trait. Since, in humans, there are many more genes on the X than there are on the Y, there are many more X-linked traits than there are Y-linked traits.

In mammals, the female is the homogametic sex, having two X chromosomes (XX), while the male is heterogametic, having one X and one Y chromosome (XY). Genes that are present on the X or Y chromosome are called sex linked genes.

In birds, the opposite is true: the male is the homogametic sex, having two X chromosomes (XX), and the female (hen) is heterogametic, having one X and one Y chromosome (XY).

Problem: What is the effect of varying eye colors in parents including wild type (red) and white on the inheritance of sex-linked traits in offspring of Drosophila (Fruit Flies)?

Hypothesis: If the phenotype of eye color in parent flies is related to inheritance of sex-linked traits in offspring, then eye color in Drosophila is a sex-linked trait located on the X chromosome.

Variables:

Independent Variable: Phenotype and Genotype for the Eye Color of Drosophila parents (wild type red vs. white)

Dependent Variable: Phenotype and Genotype for Eye Color of Drosophila offspring

Constants: Other Phenotypes and Genotypes including: body type, bristles, antennae, eye shape, wing size, wing shape, wing vein, and wing angle; room temperature; temperature of the incubator; duration of incubation.

Method (Procedure):

Materials: Male White-eyed Drosophila (fruit fly), Female wild-type red-eyed Drosophila (fruit fly), Beakers(6), Incubator, Cork stopper (6), Microscope, Sorting Brush, Slide, Ether, Calendar, Computer  

Procedure:

  1. Obtain a vial of wild- type flies. Practice immobilizing and sexing these flies. Examine these flies and note the characteristics of their eyes, wings, bristles, and antennae.
  2. To make handling easier, immobilize the flies with an ether, or by twirling the vial in ice for several minutes. Place the immobilized flies on a piece of filter paper inside a Petri dish. Place this under a dissecting microscope to view the flies.
  3.  Distinguish male flies from female flies by looking for the following characteristics:
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  1. Males are usually smaller than females.
  2. Males have dark, blunt abdomens, and females have lighter, pointed abdomens.
  3. Only males have sex combs, which are groups of black bristles on the upper most joint of the forelegs.
  1. Obtain a vial containing a mutant white-eyed male fly and a wild type red-eyed female. Record the cross number of the vial. This number will serve as a record as to which cross you obtained. These flies are the parental generation (P1) and have already mated. The female should have already laid eggs on the surface of the ...

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