GENETICS HELP PLEASE Two outwardly normal mice Generation 1

GENETICS HELP PLEASE!!!! Two outwardly normal mice (Generation 1) are mated together and produce offspring (Generation 2). When fed regular mouse chow Generation 2 mice exhibit two phenotypes: wild type and sickly, at a ratio of 3:1, respectively. You accidentally spill Chemical X onto the mouse chow and observe the sickly mice recover the wild-type phenotype. Curious, you randomly select two of the sickly mice and mate them together. In this generation (Generation 3), all the mice initially display the sickly phenotype when fed with regular mouse chow. When you feed these mice the Chemical X chow, most mice recover the wild-type phenotype though others remain sickly. As before, you observe a 3:1 ratio; 3 Chemical X sensitive to 1 Chemical X immune.

1.)Assuming Mendelian behavior of the alleles involved (i.e., true dominance), provide an explanation for the results described above.

2.) Chemical X seems to be important in determining the phenotype of the mice in question. Provide an explanation of what role it may be playing in determining the ultimate phenotypes of the mice.

3.) Given the information above, predict the genotypes of the following organisms:
i. Chemical X immune mice in Generation 3
ii. Sickly phenotype mice in Generation 2
iii. The parental mice in Generation 1

Solution

Suppose Normal mice have genotype Nn. So, Nn x Nn -----> Gives 1NN,2Nn,1nn genotype, with phenotype ratio3:1 with dominant N. NN and Nn are wild type and nn is sickly type. Chemical X may be a mutagen that is stimulating mutation at the genetic level in sickly mice where the dominant trait may be present (but hidden). It appears due to effect of mutagen. i.Chemical X immune mice in Generation 3- nn ii. Sickly phenotype mice in Generation 2-nn iii. The parental mice in Generation 1-Nn