Assume that x is a new mutant allele in corn. An x/x plant is crossed with a tri
ID: 93445 • Letter: A
Question
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 X locus (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 X locus 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)
1:1 dominant to recessive.
It means ratio of X/x and x/x is 1:1 which can be seen in the following given chart.
b)
5:1 dominant to recessive means ration of X and x is 5.1.
Gametes Progeny
X/X X/X/x
x x/x
X/x X/x/x
X/x X/x/x
X X/x
X X/x
If n + 1 pollen are viable then ratio of gametic types is 2X/x:2X:1x:1X/X and it becomes 5:1.
If n + 1 pollen are not viable then ratio of gametic types is 2X/x:1x/x and it becomes 2:1.