In rabbits,genes T and R are located on the same chromosome,20 map units apart.A colleague sends you one of his pure-breeding t r/t r males,which you cross to a T R/T R individual.Each of the T R/ t r F₁ heterozygotes is then crossed back to your colleague's double homozygous recessive.Altogether,the backcrosses produce 50 rabbits,of which 24 are T R/t r,24 are t r/t r,1 is T r/t r and 1 is t R/t r. Which of the following explanations best justifies the results? A)The colleague's rabbit is heterozygous for an inversion that spans at least 16 map units of the region between genes t and r. B)The colleague's rabbit is heterozygous for an inversion that spans at least 18 map units of the region between genes t and r. C)The colleague's rabbit is homozygous for an inversion that spans at least 16 map units of the region between genes t and r. D)The colleague's rabbit is homozygous for an inversion that spans at least 18 map units of the region between genes t and r. E)The colleague's rabbit carries an inversion that spans the whole region between genes t and r.

Question

Quizplus · Accepted Answer

The presence of only 2 recombinant offspring out of 50 (1 T r/t r and 1 t R/t r) suggests a very low recombination frequency, much lower than the expected 20% based on the map distance between genes T and R. This can be explained by a homozygous inversion spanning at least 16 map units, which suppresses recombination in the inverted region. Since the recombination is not completely suppressed (as indicated by the presence of 2 recombinant offspring), the inversion must not span the entire region between the genes, making option C the best explanation.

In Rabbits,genes T and R Are Located on the Same