Question

The Gila monster is a species of venomous lizard native to the limited States. When a true-breeding lizard with green scales from the southwestern USA is mated with a true-breeding lizard with brown scales from northwestern Mexico, the F, progeny all had brown scales. When these F. lizards are intercrossed, the tz appear in a ratio of 12/16 with brown scales to 4/16 with green scales ( : 3:3 :1 - 12- 1 a. Using the notation with underscores to represent homo/heterozygous dominant genotypes in the F2 Bive genotypes for the green and brown scaled Gila monster individuals in these crosses for the P, F and F2 generations. Phenotype Genotypes) queen sales bb99 brown scales BBGG F1 brown scales BbGg F2 brown scales B -G- green scales bb99 b. Draw a branch diagram to show how this ratio of Fa progeny could have arisen from this cross. BG

Answer 1

Let us assume that allele B is dominant over allele b.

Therefore, BB and Bb will give brown scales while bb will give green scales.

P          Phenotype       Genotype

            Brown scales BB

            Green scales   bb

F1        Brown scales Bb

F2        Brown scales B_

            Green scales   bb

b. F1 generation Bb    x          Bb

gametes           1/2B, 1/2b       1/2B, 1/2b