Q6. Drosophila pure-breeding for long (wildtype) wings and brown eyes were cross
ID: 3164856 • Letter: Q
Question
Q6. Drosophila pure-breeding for long (wildtype) wings and brown eyes were crossed to Drosophila pure-breeding for short wings and red (wildtype) eyes. The F? generation was all wildtype. F females were crossed to homozygous recessive males. The following results were obtained for 800 progeny: Phenotype Wildtype Brown eyes Short wings Short wings and brown eyes Number 74 336 304 86 a) Assuming that each trait is controlled by one gene that has two alleles, which is the dominant allele for b) c) d) each of the traits? Define appropriate gene and allele symbols. Using your symbols, write out the cross, showing the genotypes and phenotypes for all generations. You must show linkage in the way you write the genotypes. Indicate which genotypes of gametes produced by the F? females (and thus which phenotypes in the final generation) are recombinant and which are non-recombinant. Calculate the recombination frequency demonstrated by this experiment.Explanation / Answer
Answer:
a).
Wild-wings (S) are dominant over short-wing(s).
Wild-eyes(R) are dominant over brown eyes(r).
b).
Wild-wings, brown eyes (Sr/Sr) x Short-wings, red eyes (sR/sR)----Parents
Sr/sR (wild-wings & Wild-eyes)-------------F1
Wild-wings (S) are dominant over short-wing(s).
Wild-eyes(R) are dominant over brown eyes(r).
The genes are linked in trans configuration, Sr/sR (F1)
c).
Sr/sR genotype produces four types of SR, Sr, sR & sr.
Sr & sR are non-recombinant gametes, which produce non-recombinat progeny and SR & sr are recombinant gametes, which produce recombinant progeny.
d).
Recombinant progeny are Wild type & short wings and brown eyes.
Recombination frequency = (No. of recombinant progeny / Total progeny ) 100
= (160/800)100 = 20%
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