The genes short legs (sl), plexus (px) and brown eyes (bn) are linked on the sec
ID: 178084 • Letter: T
Question
The genes short legs (sl), plexus (px) and brown eyes (bn) are linked on the second chromosome of Drosophila. In a cross of bn sl px / + + + females with bn sl px / bn sl px males, the following progeny were counted.
The genotypes of the nonrecombinant parental type are
A. bn sl px / bn sl px and bn + + / bn sl px
B. bn sl px / bn sl px and + + px / bn sl px
C. + + + / bn sl px and bn sl px / bn sl px
D. bn + px / bn sl px and + sl + / bn sl px
E. None of the above
The genotypes of the double crossover are A. bn sl px / bn sl px and bn + + / bn sl px
B. bn sl px / bn sl px and + + px / bn sl px
C. + + + / bn sl px and bn sl px / bn sl px
D. bn + px / bn sl px and + sl + / bn sl px
E. None of the above
The gene order is
A. bn – sl – px
B. sl – bn – px
C. px – sl – bn
D. Either answer A or answer C. The data do not distinguish between the two possibilities.
E. None of the above is correct
Explanation / Answer
Answer:
1). C). + + + / bn sl px and bn sl px / bn sl px
The nonrecombinant parental type are always more in number than the any recombinants.
2). D). bn + px / bn sl px and + sl + / bn sl px
Doble recombinant types are always small in number than any other genotype in three point test cross.
3). D. Either answer A or answer C. The data do not distinguish between the two possibilities.
The gene for short legs (sl) is middle between plexus (px) and brown eyes (bn) genes.