Semisterility in corn, as seen by unfilled ears withgaps due to abortion of approximately half the ovules,is an indication that the strain is a translocation heterozygote. The chromosomes involved in the translocation can be identified by crossing the translocationheterozygote to a strain homozygous recessive for agene on the chromosome being tested. The ratio ofphenotypic classes produced from crossing semisterileF1 progeny back to a homozygous recessive plant indicates whether the gene is on one of the chromosomesinvolved in the translocation. For example, a semisterilestrain could be crossed to a strain homozygous for the yg mutation on chromosome 9. (The mutant has yellowgreen leaves instead of the wild-type green leaves.) Thesemisterile F1 progeny would then be backcrossed tothe homozygous yg mutant.a. What types of progeny (fertile or semisterile, greenor yellow-green) would you predict from the backcross of the F1 to the homozygous yg mutant if thegene was not on one of the two chromosomesinvolved in the translocation?b. What types of progeny (fertile or semisterile, greenor yellow-green) would you predict from the backcross of the F1 to the homozygous mutant if the yggene is on one of the two chromosomes involvedin the translocation?c. If the yg gene is located on one of the chromosomes involved in the translocation, a few fertile,green progeny and a few semisterile, yellow-greenprogeny are produced. How could these relativelyrare progeny classes arise? What genetic distancecould you determine from the frequency of theserare progeny?
Semisterility in corn, as seen by unfilled ears with
gaps due to abortion of approximately half the ovules,
is an indication that the strain is a translocation heterozygote. The chromosomes involved in the translocation can be identified by crossing the translocation
heterozygote to a strain homozygous recessive for a
gene on the chromosome being tested. The ratio of
phenotypic classes produced from crossing semisterile
F1 progeny back to a homozygous recessive plant indicates whether the gene is on one of the chromosomes
involved in the translocation. For example, a semisterile
strain could be crossed to a strain homozygous for the yg mutation on chromosome 9. (The mutant has yellowgreen leaves instead of the wild-type green leaves.) The
semisterile F1 progeny would then be backcrossed to
the homozygous yg mutant.
a. What types of progeny (fertile or semisterile, green
or yellow-green) would you predict from the backcross of the F1 to the homozygous yg mutant if the
gene was not on one of the two chromosomes
involved in the translocation?
b. What types of progeny (fertile or semisterile, green
or yellow-green) would you predict from the backcross of the F1 to the homozygous mutant if the yg
gene is on one of the two chromosomes involved
in the translocation?
c. If the yg gene is located on one of the chromosomes involved in the translocation, a few fertile,
green progeny and a few semisterile, yellow-green
progeny are produced. How could these relatively
rare progeny classes arise? What genetic distance
could you determine from the frequency of these
rare progeny?
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