The human kidney filters the blood to retain useful substances and remove waste products and excess water as urine. SLCSA1 and SLC7A9 are two different genes that each encode one part
of a transporter protein complex typically found in the plasma membrane of human kidney cells. This transporter complex moves certain amino acids across the plasma membrane of the cells.
Mutations in both the SLCSA 1 and SLC7A9 genes are associated with increased levels of the polar amino acid cysteine in the urine, a condition called cystinuria. A researcher identified seven
individuals with a family history of cystinuria. The researcher measured the concentration of cysteine in the urine of the seven individuals and sequenced their SLCSA and SLC7A9 genes to
determine whether they carry functional (+) or mutant (-) alleles of genes. The results are shown in Table 1
TABLE 1. CHARACTERISTICS OF SEVEN INDIVIDUALS WHO CARRY AT LEAST ONE MUTANT ALLELE
+ indicates the presence of a functional allele and
indicates the presence of a mutant allele
Individual
SLC7A 9 Alleles
+/-
Concentration of Cysteine in Urine Relative to Normal Values
32.2
29.8
11.0
SLCSA 1 Alleles
--
+-
-/-
+/+
--
-
8.8
0
7.7

+/+
--
+/+
+-
+/+
2.3
+/+
0.5
+-
(a) Identify the individual who most likely exhibits symptoms of cystinuria.