IB Bio 2 - IHS
LINKED GENES PROBLEM SET – tomatoes, fruit flies, chickens!
Directions: Work out these problems in your journal, using careful, neat work. Circle your answers!
1. In tomatoes, vine height and fruit shape are linked. Tall vines are dominant to dwarf vines, and
round fruit (tomatoes) is dominant to pear-shaped tomatoes. When a dwarf tomato plant with
pear-shaped tomatoes is crossed to a true-breeding tall tomato plant with round tomatoes, all the
first generation offspring are tall with round tomatoes. When these first-generation plants are
subjected to a test cross with the parent dwarf pear-shaped tomato plant, these progeny are
obtained:
229 tall, round
23 tall, pear-shaped
27 dwarf, round
221 dwarf, pear-shaped
a) Diagram the linkage groups of all the tomato plants in this problem (parents, F-1, and test cross
offspring)
b) Calculate % crossover between the height and shape genes.
c) How far apart are these two genes?
2. In Drosophila, a gene for eye color (wild-type red is dominant to vermillion) and wing shape
(wild type long is dominant to cut) are linked and both are on the X chromosome. Use the symbols
v+ and v for the eye color alleles, and c+ and c for the wing shape alleles. A male fruit fly with
vermillion eyes and cut wings is mated to a red-eyed, long-winged female that is heterozygous for
both genes. The following progeny result:
426
69
61
444
cut, vermillion
cut, red
long, vermillion
long, red
a) Diagram the linkage groups of the parents and the above progeny.
b) What is the % crossover between these two genes?
c) How far apart are these two genes?
3. Assume that, in chickens, feather color and amount of down are linked. The allele for silver
plumage (S) is at locus 12.0, and the allele for light down (Li) is at locus 28.0 on the same
chromosome. As you can tell from the use of the capital letters, both alleles are dominant over
their corresponding wild-type alleles (red plumage S+ and moderate down, Li+). What percent
of the various types of progeny would be expected from a cross with these linkage groups:
S+
Li
____________
____________
S
Li+
x
S+
Li+
___________
___________
S+
Li+
IB Bio 2 - IHS
LINKED GENES PROBLEM SET – tomatoes, fruit flies, chickens!
Directions: Work out these problems in your journal, using careful, neat work. Circle your answers!
1. In tomatoes, vine height and fruit shape are linked. Tall vines are dominant to dwarf vines, and
round fruit (tomatoes) is dominant to pear-shaped tomatoes. When a dwarf tomato plant with
pear-shaped tomatoes is crossed to a true-breeding tall tomato plant with round tomatoes, all the
first generation offspring are tall with round tomatoes. When these first-generation plants are
subjected to a test cross with the parent dwarf pear-shaped tomato plant, these progeny are
obtained:
229 tall, round
23 tall, pear-shaped
27 dwarf, round
221 dwarf, pear-shaped
a) Diagram the linkage groups of all the tomato plants in this problem (parents, F-1, and test cross
offspring)
b) Calculate % crossover between the height and shape genes.
c) How far apart are these two genes?
2. In Drosophila, a gene for eye color (wild-type red is dominant to vermillion) and wing shape
(wild type long is dominant to cut) are linked and both are on the X chromosome. Use the symbols
v+ and v for the eye color alleles, and c+ and c for the wing shape alleles. A male fruit fly with
vermillion eyes and cut wings is mated to a red-eyed, long-winged female that is heterozygous for
both genes. The following progeny result:
426
69
61
444
cut, vermillion
cut, red
long, vermillion
long, red
a) Diagram the linkage groups of the parents and the above progeny.
b) What is the % crossover between these two genes?
c) How far apart are these two genes?
3. Assume that, in chickens, feather color and amount of down are linked. The allele for silver
plumage (S) is at locus 12.0, and the allele for light down (Li) is at locus 28.0 on the same
chromosome. As you can tell from the use of the capital letters, both alleles are dominant over
their corresponding wild-type alleles (red plumage S+ and moderate down, Li+). What percent
of the various types of progeny would be expected from a cross with these linkage groups:
S+
Li
____________
____________
S
Li+
x
S+
Li+
___________
___________
S+
Li+