Sex-Linked Inheritance in Drosophila Melanogaster

Description
In the majority of cases, the sex of an individual is determined by a pair of genes on the sex chromosome. Females are homozygous and males are heterozygous. Sex-linked inheritance is defined as the inheritance of somatic characters, which are linked with sex chromosomes (X and Y). The characters are described as sex-linked characters. The phenomenon of sex linkage was first observed by T.H. Morgan in 1910 while experimenting on Drosophila. Morgan observed the appearance of white eye color in males in the cultures of normal wild-eyed flies. He thus proposed the phenomenon of sex linkage.

In the present experiment, we have taken the yellow-body mutant and crossed it with an OK strain to understand the pattern of sex-linked inheritance.

Materials

• OK strains of Drosophila melanogaster
• Yellow-body mutants
• Media bottles
• Anaesthetic ether
• Etherizer

Procedure
Drosophila melanogaster: The OK strain and the yellow-body flies are cultured in standard media separately. When the pupa are ready to close the bottles, the bottles are cleaned by taking out all the flies present. From the pupa, the virgin females were isolated and aged for 2–3 days, and then the crosses are conducted as follows:

• Yellow-body females × OK males
• Yellow-body males × OK females

The progeny produced in the F1 are observed for phenotype and the data are recorded. Some of the yield F1 progenies were inbred to yield the F2 generation, which were also observed, and the data was recorded.

Direct Cross
Parents	yellow females × OK males
Fl	all F1 females wewe grey-bodied and males were yellow
Inbreed	F1 females × F1 males
F2	grey female :	grey male :	yellow female :	yellow male:
Ration	46 :	61 :	51 :	50 :
Phenotype	Observed	expected	Deviation	d2	d2/E = X
grey-bodied male	61	52	9	81	1.5
grey-bodied female	46	52	-6	36	0.6
yellow bodied female	51	52	1	1	0.01
yellow bodied male	50	52	-2	4	0.07
ΣX2 = 2.18
Degree of freedom = 4 – 1 = 3

Reciprocal Cross
Parents	yellow females × OK males
Fl	all flies are grey bodied
Inbreed	F1 females × F1 males
F2	grey female :	grey male :	yellow female :	yellow male:
Ration	63 :	52 :	48 :	48 :
Phenotype	Observed	expected	Deviation	d2	d2/E = X
grey-bodied male	115	122.25	7.25	52.56	0.4
grey-bodied female
yellow bodied female	48	40.75	-7.25	52.56	1.2
yellow bodied male
ΣX2 = 1.71
Degree of freedom = 3 – 1 = 2