December 14, 2005.
Question 1. (Total = 10 points)
Tomatoes can be tall or dwarf, smooth or peachy, and round or oblate.
When a single tall, smooth and
round plant was crossed to a group of pure-breeding dwarf, peachy and oblate plants, the following
progeny were obtained:
155 tall, smooth, round
33 tall, smooth, oblate
11 tall, peach, oblate
2 tall, peach, round
158 dwarf, peach, oblate
29 dwarf, peach, round
12 dwarf, smooth round
0 dwarf, smooth oblate
a. What would have been the results if the same individual tall, smooth and round plant had been crossed
to another group of pure-breeding tall, smooth, round plants?
(2 pts) You would get all tall, smooth, and round plants since these
traits are dominant and a pure-breeding tall, smooth, round plant would be
homozygous for all traits. You know that they are dominant because the
original dwarf, peachy, oblate tomato was pure-breeding. If these traits
were dominant, all the progeny would have been dwarf, peachy, and oblate.
b. If the single individual
tall, smooth and round plant used in these crosses was the progeny of a cross
between two individuals from pure-breeding lines, what were the phenotypes of the pure-breeding
(3 pts) The parents must have been tall, smooth, and round X dwarf,
peachy, and oblate. Since you get all categories of progeny, you know that
the individual tall, smooth, and round plant used is a heterozygote for all
traits. Thus, it must have received a its dominant copies from one
pure-breeding parent and its recessive copies from the other pure-breeding
c. Draw as precise a genetic map as possible for the three genes.
Call the genes “size”, “skin texture” and
size -- 6.25 m.u. -- skin texture -- 16 m.u. – shape
size-skin texture = ((11+12+2+0)/400) X 100 = 6.25 m.u. or centimorgans
skin texture-shape = ((33+29+2+0)/400) X 100 = 16.0 m.u. or centimorgans
size-shape = ((33+11+29+12+(2X2)+(0X2)/400) X 100 = 22.25 m.u. or