16. You are studying a species of fruit fly, Drosophila mitensis, and you find a fly that has cut wings as seen here (use “w+” as wild type allele and “cut” as cut wings allele):
The normal F1 female progeny from the cross in (a) were crossed to the normal F1 males. The resulting F2 progeny were:
1/2 normal females
1/4 normal males
1/4 cut-wing males
What is the mode of inheritance of cut wing, and what were the genotypes of the following? (8 marks)
Parents ________
F1 ________
F2 _______
Parents: w+/w+
F1: w+/cut
F2: 1/2 w+/w+, 1/4 w+/cut, 1/4 cut/cut
Mode of inheritance of cut wing: Recessive
The mode of inheritance of cut wing in the fruit fly species Drosophila mitensis can be determined based on the ratios observed in the F2 progeny.
From the information given, we can deduce the following:
Parents: The initial cross (a) involved an unspecified female with cut wings (genotype: cut/cut) and a male with normal wings (genotype: w+/w+).
F1: The normal F1 female progeny from the cross in (a) were crossed to the normal F1 males. This means the F1 females must have been heterozygous for the cut wing allele (genotype: w+/cut), while the F1 males were homozygous for the normal wing allele (genotype: w+/w+).
F2: The resulting F2 progeny were as follows:
- 1/2 normal females (w+/w+)
- 1/4 normal males (w+/w+)
- 1/4 cut-wing males (w+/cut)
From these ratios, we can determine that the cut wing allele exhibits a recessive inheritance pattern. This means that for an individual to express the cut wing phenotype, they must have two copies of the cut wing allele (genotype: cut/cut).
Therefore, the genotypes of the following are:
- The female parent (a): cut/cut (since she had cut wings)
- The male parent (a): w+/w+ (since he had normal wings)
- The F1 females: w+/cut (heterozygous for cut wing allele)
- The F1 males: w+/w+ (homozygous for normal wing allele)
- The F2 normal females: w+/w+ (homozygous for normal wing allele)
- The F2 normal males: w+/w+ (homozygous for normal wing allele)
- The F2 cut-wing males: w+/cut (heterozygous for cut wing allele)
Note: The above genotypes are based on the assumption that the cut wing allele is represented by the "cut" symbol and the wild type allele is represented by "w+".