Filtrate becomes less concentrated as it flows down the medullary collecting ducts. True or False

False.

Explanation:

At the medullary collecting ducts there is variable and further reabsorption of water, sodium , potassium, hydrogen and bicarbonate. It become freely permeable to water solute. The outer medulary duct raise the concentration of intraluminal urine and the inner medulary duct allow maximally concentration of urine due to osmotic water equilibration

this is true, assuming that the allele is completely recessive and incomplete dominance is not a factor.