GENETICS Drosophilia females that are heterozygous for three recessive mutations
ID: 53498 • Letter: G
Question
GENETICS
Drosophilia females that are heterozygous for three recessive mutations [ e (ebony body), st (scarlet eyes), and ss (spineless bristles)] were testcrossed, and the following progeny were obtained. NOTE: the ‘+’ symbol in the table below represents the wild type phenotype; E represents the mutant phenotype of ebony body; ST represents the mutant phenotype of scarlet eyes, and SS represents the mutant phenotype of spineless bristles.
F1 Phenotype
Number of Offspring
+ (or +, +, +)
67
E, +, +
8
E, ST, +
68
E, +, SS
347
E, ST, SS
78
+, ST, +
368
+, ST, SS
10
+, +, SS
54
Identify the F1 phenotype categories that represent offspring receiving a gamete containing a chromosome that is the result of a double cross over event.
A) +,+,+ and E,ST, SS
B) E, +, SS and +, ST, +
C) E, +, + and + ST, SS
E) +, ST, SS and +, + SS
F) +, +, + and E, +, +
F1 Phenotype
Number of Offspring
+ (or +, +, +)
67
E, +, +
8
E, ST, +
68
E, +, SS
347
E, ST, SS
78
+, ST, +
368
+, ST, SS
10
+, +, SS
54
Explanation / Answer
Double crossover are always least in number. so its option C.
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