Question

8) You just isolated a new strain of mutant mice, and preliminary mating suggest that the new mutant phenotype is not inherited in an autosomal fashion. Circumstantial evidence seems to indicate that the mutant phenotype may be following either an X-linked dominant or a mitochondrial-type inheritance pattern. Assume the mice are true breeding.

a) What informative crosses would you set up to distinguish between these two possibilities?

b) How would you interpret your results?

9. You are crossing two individuals with genotypes R/R q/q and r/r Q/Q. The R and Q genes are located on different chromosomes (unlinked), which means that four F1 gametes should be produced.

a) What is the F1 genotype, and F1 gametes?

b) Of the four gametes produced by the F1 individuals, which are parental and which are recombinant? 10. A three-point cross was performed between a heterozygous organism and a homozygous recessive testcross organism. One of the most frequent progeny classes got a chromosome with the genes a, B, C from the heterozygous parent, while one of the least frequent progeny classes got the genes A, B, C.

a) Draw out the crossover that occurs. b) What is the genotype of the other “most frequent” progeny class?

c) What is the genotype of the other “least frequent” progeny class? d) Based on the answers to (a) and (b), what is the order of the A, B and C genes on the chromosome?

Answer 1

8.

b) If the phenotype is X-linked dominant, then in the F1 of the first cross, all individuals should be affected (males and females); and in the F1 of the second cross, all the females but none of the males should be affected.
If it's mitochondrial inheritance then in the F1 of the first cross, all individuals should be equally affected (males and females); but in the F1 of the second cross, nobody should be affected.

9. F1 genotype R/r q/Q
F1 gametes Rq, RQ, rq, rQ

Rq and rQ are parental, rq and RQ are recombinant