GAL1 genes are unlinked was established by tetrad analysis.You should think about what the tetrads from the aforementioned diploids would look like. Put together the simplest model is that Gal4 is a positive regulator of Gal1 (and the other Gal4 Gal1 Gal genes).The sign indicates that Gal4 increases Gal expression,but does not indicate whether this is direct or indirect. Gal80 mutant:The next useful Analysis of Gal80 regulatory mutant isolated was Gal80, Gal80-is constitutive in which the Gal1 encoded galactokinase Gal80*/Gal80-is regulated: is expressed even in the absence of therefore Gal80-is recessive galactose and is not further induced in MATa Gal1-Gal80+x MATa Gal1+Gal80- its presence.Again,heterozygous 1 4 1 diploids(Gal80/wt)showed that Type 1 Type 2 Type 3 uninducible uninducible uninducible Gal80 is recessive,Tetrad analysis uninducible uninducible uninducible showed that Gal80 is not linked to Gal1, constitutive constitutive regulated(wt) constitutive regulated (wt) regulated (wt) Gal4 or any of the Gal genes. If a mutant Gal80 results in constitutive Gal1 expression,the simplest model is that Gal80 negatively regulates the Gal genes.Since Gal4 positively regulates,and Gal80 negatively regulated Gal1 expression,we have to figure out how these two gene products work together to achieve such regulation. Assuming that Gal4 and Gal80 act in series there are two formal possibilities: Model 1 Model 1 is that Gal4 positively regulates Gal1, and that Gal80 negatively galactose regulates Gal4;the Gal80 Gal4 Gal1 presence of galactose somehow inhibits Gal80 Model 2 function thus releasing Gal4 to positively activate ⊙ Gal1 expression. galactose Model 2 is that Gal80 Gal4 ⊙、 6al80 Gal1 negatively regulates Gal1,and Gal4 negatively regulates Gal80;here the presence of galactose positively activates Gal4 which in turn negatively regulates Gal80,thus relieving inhibition of Gal1 expression.GAL1 genes are unlinked was established by tetrad analysis. You should think about what the tetrads from the aforementioned diploids would look like. Put together the simplest model is that Gal4 is a positive regulator of Gal1 (and the other Gal genes). The + sign indicates that Gal4 increases Gal expression, but does not indicate whether this is direct or indirect. Gal80 mutant: The next useful regulatory mutant isolated was Gal80- , in which the Gal1 encoded galactokinase is expressed even in the absence of galactose and is not further induced in its presence. Again, heterozygous diploids (Gal80- /wt) showed that Gal80- is recessive, Tetrad analysis showed that Gal80 is not linked to Gal1, Gal4 or any of the Gal genes. If a mutant Gal80 results in constitutive Gal1 expression, the simplest model is that Gal80 negatively regulates the Gal genes. Since Gal4 positively regulates, and Gal80 negatively regulated Gal1 expression, we have to figure out how these two gene products work together to achieve such regulation. Assuming that Gal4 and Gal80 act in series there are two formal possibilities: Model 1 is that Gal4 positively regulates Gal1, and that Gal80 negatively regulates Gal4; the presence of galactose somehow inhibits Gal80 function thus releasing Gal4 to positively activate Gal1 expression. Model 2 is that Gal80 negatively regulates Gal1, and Gal4 negatively regulates Gal80; here the presence of galactose positively activates Gal4 which in turn negatively regulates Gal80, thus relieving inhibition of Model 1 Model 2 Model 1 Model 2 Gal1 expression