PBC-xxxx L Genetics Lab
FALL 2009
Department of Biological Sciences
Florida International University
Brassica rapa as a model for human genetics – Paternity Exclusion
Objective
In this lab the students will learn how to perform paternity testing by using the fastplants Brassica rapa
as human model organisms. The students will use molecular markers, as well as Mendelian markers,
to perform paternity exclusion.
What are Fastplants?
Wisconsin Fast Plants TM (Brassica rapa) are rapid-cycling brassicas. They are members of the
crucifer family of plants, closely related to cabbage and turnips that have been bred over 30 years at
the University of WIsconsin - Madison. These petite plants (~20 cm tall at maturity) have an ultrashort life cycle in about 40 days (35-45 d). In just over a month seeds can be planted, plants grown,
flowers can be pollinated, and new seeds harvested (Who’s the father?, Carolina) Fastplants grow
under relatively simple conditions, except for the requirement of fluorescent lightning 24 h/d.
Therefore, those plants are ideal for use in a wide range of instruction such as botany, ecology,
physiology and genetics (Wendell and Pickard, 2007).
Why do we use Brassica rapa as a human model system?
Despite being members of the plant kingdom, B. rapa can be used as a relevant model organism for
teaching human genetics, because they share two important features with humans: 1) they do not selfpollinate, and 2) they are genetically diverse. Even though they have perfect flowers, they are selfincompatible for mating (an individual plant will reject its own pollen), so it is very easy to mate two
individuals by simply transferring pollen from one to another with no risk of self-pollination. If seeds
are then collected from only one of the partners, it becomes the “mother” and the other must be the
“father,” and, by properly arranging matings, any type of human family structure can be easily
replicated. Self-incompatibility also preserves genetic diversity within B. rapa strains. Members of the
same strain of B. rapa, such as the Fast Plants strains obtained from Carolina Biological Supply
(Burlington,NC) may be superficially uniform because they are true-breeding for a particular leaf
color, stem color, or hairiness, but analysis of DNA markers reveals that in fact each individual plant
is genetically unique.
To create a paternity dispute with the B. rapa, one cotton swab is rolled over the anthers of two
different plants (Alleged Fathers 1 and 2). The pollen-laden swab is then used to pollinate a third plant
(the Mother). Seeds from the Mother are sown, and one seedling is used as the Child (Wendell and
Pickard, 2007).
Part 1: Pollination
Background information:
The flowers bloom when the B.rapa plants are 13-20 days old. At the growth tip, new flower buds
begin to appear. Each bud is protected by four green sepals. Once a flower opens, the sepals are
hidden beneath four bright yellow petals. The flower’s center boasts a single pistil, which is the
female part of the flower. The pistil is surrounded by six yellow stamens, which are the male parts of
the flower. Each stamen is covered with lots of powdery, yellow pollen. The bright yellow petals may
catch your eye — and the eye of insects. The petals form a beacon that lets insects know that there is
food available. Hidden deep inside the flower are nectaries, which produce nectar. Nectar is a sweet,
sugar-rich substance that insects love to eat. That’s why bees and butterflies are attracted to flowers —
they’re hungry! In exchange for food, insects pollinate flowers. When an insect moves from flower to
flower looking for nectar, pollen from each flower gets caught in the insect’s body hairs and is
transferred to other flowers. After pollen has landed on the tip of another flower’s pistil, it grows a
tube down into the pistil, where the eggs are housed. Sperm (from inside the pollen) are then able
move down the tube until they reach the eggs and fertilize them. The fertilized eggs then become the
embryos of new seeds (Who’s the father, Carolina).
Pollination-Procedure:
Use beesticks or q-tips.
1. Brush beestick or q-tip over stamen of one flower to
pick up pollen and brush of pollen on the pistil of
another plant. The pollen must be transferred back
and forth among the plant which is designated as the
mother plant and the two father plants (crosspollination). Ideally, one student of each group
should repeat the procedure one day after the first
pollination.
2. It is important to pinch off unopened buds on the last
day of pollination to avoid the generation of seeds
which might have been pollinated before we started our experiment.
3. Note which plant is the mother plant and which are the father plants. Label your plants with
date and group-name.
4. One -two leaves should be collected from each plant and stored in the fridge. Make sure to
label which leaf belongs to the mother- and which to the alleged fathers. You will need this
leaves later on in this term to extract DNA for the paternity testing.
Part 2: Seed collection (3 weeks after pollination)
Information:
After pollination, seed pods and seeds will develop. The seed pods will begin to elongate within 3-5
days and the flower petals will drop off. The seeds need 20 days to mature. Twenty days after
pollination the plants must be removed from the water and dried for 5 days. Then, the seeds from the
mother can be sown, and 1-2 seedlings can be used as the children (Who’s the father, Carolina).
Seed collection procedure:
Dry seed pods must be rolled between hands over a paper towel and stored in a cool, dry place until
ready to plant [Carolina, Growing Instructions].
Part 3: Growing Instructions
Materials needed:

Seeds harvested from mother plants

Planting pots

Potting soil

Diamond wicks – conduct water from water mat to the soil in the pots.

Water mat- conducts water from reservoir to wicks.

Water reservoir

Fertilizer pellets

Anti-Algae squares

Plant labels

Pipets

Fluorescent light system
Growing Instructions :
1. Fill reservoirs with water and drop in blue algae-control squares. Snap on lid.
2. Saturate the water mat with water and lay it on reservoir lid. The end of the mat must extend
into the water. Make sure that the mat is thoroughly wet.
3. Drop one wick into each planting pot so that the tip extends halfway out of the whole in the
bottom of the pot (about 2 cm).
4. Moisten the soil slightly and fill each pot halfway with soil.
5. Add 2-3 fertilizer pellets to each pot (depends on size of pot) and fill each cell to the top with
moistened soil.
6. With your finger make shallow depressions on top of each cell. Do not press hard and compact
the soil. Then, drop 2-3 seeds in each depression and sprinkle enough soil to cover seeds in
each pot.
7. Water very gently with pipet until water drips from each wick. Be careful not to wash seeds
out of pots. Seeds must be watered from the top with pipets for the first 3 days.
8. Label each pot with groups name and date and place the pots on the water mat. Remember to
keep the water- reservoirs full with water at all times.
9. The top of the pots must be positioned 5-10 cm below the fluorescent light.