Which of the following would likely produce a dog with the darkest fur?
(A) High levels of LSFR and high levels of DRKFR
(B) High levels of LSFR and low levels of DRKFR
(C) Low levels of LSFR and high levels of DRKFR
(D) Low levels of LSFR and low levels of DRKFR

A gene responsible for production of hair pigment in dogs is called Fursilla (frsl). A map of the Fursilla locus is shown in Figure 1, below. When expressed, it results in darkly pigmented dog fur. When unexpressed, the hair is devoid of pigmentation and appears pure white. Expression of Fursilla (frsl) depends on the binding/lack of binding of several proteins: Nefur (NEFR), Lesfur (LSFR), and Dirkfur (DRKFR). Figure 2 shows the relative levels of frsl transcript as measured via RT-qPCR when each protein is overexpressed or unexpressed in the cell.

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mRNA levels 900 800 700 600 500 400 300 200 100 0 1220 Start site 1295 Figure 1. Map of the Fursilla region of chromosome 8 Levels of Fursilla transcript NEFR DRKFR LSFR Protein Overexpressed in the Cell mRNA levels 800 700 600 500 400 300 200 100 0 1617 Levels of Fursilla transcript NEFR DRKFR Protein Unexpressed in the Cell LSFR