Question 1 (6 points) Assume that x is a new mutant allele in corn. An x/x plant

Question

Question 1 (6 points) Assume that x is a new mutant allele in corn. An x/x plant is crossed with a triple-10 individual (trisomic for chromosome 10 only) carrying only wild-type dominant alleles at the Xlocus (Cross 1). Trisomic progeny for chromosome 10 are recovered and crossed back to the x/x plant (Cross 2). (a) What ratio of dominant to recessive phenotypes is expected if the X locus is not in chromosome 10? (Hint: Write out the parental and progeny genotypes for the Xlocus for both Cross 1 and Cross 2 keeping in mind that it is not on chromosome 10) (b) What ratio of dominant to recessive phenotypes is expected if the X locus is in chromosome 10? (Hint: Write out the parental and progeny genotypes for the X locus for both Cross 1 and Cross 2 keeping in mind that it now is on chromosome 10)

Explanation / Answer

(a) A test cross of F1 hybrid with homozgous recessive parent gives dominant and recessive progeny in 1:1 ratio.
(b) Provided the trisomic pollens are viable, the ratio of dominant to recessive progeny will be 5: 1 respectively.

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