Nearly every cultivated Cannabis plant, no matter
what its future, began as a germinating seed; and nearly all
Cannabis cultivators, no matter what their intention, start
with seeds that are gifts from a fellow cultivator or ex-
tracted from imported shipments of marijuana. Very little
true control can be exercised in seed selection unless the
cultivator travels to select growing plants with favorable
characteristics and personally pollinate them. This is not
possible for most cultivators or researchers and they usually
rely on imported seeds. These seeds are of unknown par-
entage, the product of natural selection or of breeding by
the original farmer, Certain basic problems affect the
genetic purity and predictability of collected seed.
1 - If a Cannabis sample is heavily seeded, then the
majority of the male plants were allowed to mature and
release pollen, Since Cannabis is wind-pollinated, many
pollen parents (including early and late maturing stami-
nate and hermaphrodite plants) will contribute to the seeds
in any batch of pistillate flowers. If the seeds are all taken
from one flower cluster with favorable characteristics, then
at least the pistillate or seed parent is the same for all those
seeds, though the pollen may have come from many differ-
ent parents. This creates great diversity in offspring.
2 - In very lightly seeded or nearly sinsemilla Can-
nabis, pollination has largely been prevented by the removal
of staminate parents prior to the release of pollen. The few
seeds that do form often result from pollen from hermaph-
rodite plants that went undetected by the farmer, or by
random wind-borne pollen from wild plants or a nearby
field. Hermaphrodite parents often produce hermaphrodite
offspring and this may not be desirable.
3 - Most domestic Cannabis strains are random hy-
brids. This is the result of limited selection of pollen par-
ents, impure breeding conditions, and lack of adequate
space to isolate pollen parents from the remainder of the
crop.
When selecting seeds, the propagator will frequently
look for seed plants that have been carefully bred locally
by another propagator. Even if they are hybrids there is a
better chance of success than with imported seeds, pro-
vided certain guidelines are followed:
1 - The dried seeded flower clusters are free of
staminate flowers that might have caused hermaphrodite
pollinations.
2 - The flowering clusters are tested for desirable
traits and seeds selected from the best.
3 - Healthy, robust seeds are selected. Large, dark
seeds are best; smaller, paler seeds are avoided since these
are usually less mature and less viable.
4 - If accurate information is not available about the
pollen parent, then selection proceeds on common sense
and luck. Mature seeds with dried calyxes in the basal por-
tions of the floral clusters along the main stems occur in
the earliest pistillate flowers to appear and must have been
pollinated by early-maturing pollen parents. These seeds
have a high chance of producing early-maturing offspring.
By contrast, mature seeds selected from the tips of floral
clusters, often surrounded by immature seeds, are formed
in later-appearing pistillate flowers. These flowers were
likely pollinated by later-maturing staminate or hermaphro-
dite pollen parents, and their seeds should mature later and
have a greater chance of producing hermaphrodite off-
spring. The pollen parent also exerts some influence on the
appearance of the resulting seed. If seeds are collected
from the same part of a flower cluster and selected for
similar size, shape, color, and perianth patterns, then it is
more likely that the pollinations represent fewer different
gene pools and will produce more uniform offspring.
5 - Seeds are collected from strains that best suit the
locality; these usually come from similar climates and lati-
tudes. Seed selection for specific traits is discussed in detail
in Chapter III.
6 - Pure strain seeds are selected from crosses between
parents of the same origin.
7 - Hybrid seeds are selected from crosses between
pure strain parents of different origins.
8 - Seeds from hybrid plants, or seeds resulting from
pollination by hybrid plants, are avoided, since these will
not reliably reproduce the phenotype of either parent.
Seed stocks are graded by the amount of control ex-
erted by the collector in selecting the parents.
Grade #1 - Seed parent and pollen parent are known and
there is absolutely no possibility that the seeds resulted
from pollen contamination.
Grade #2 - Seed parent is known but several known stami-
nate or hemaphrodite pollen parents are involved.
Grade #3 - Pistillate parent is known and pollen parents
are unknown.
Grade #4 - Neither parent is known, but the seeds are col-
lected from one floral cluster, so the pistillate seed parent-
age traits may be characterized.
Grade #5 - Parentage is unknown but origin is certain,
such as seeds collected from the bottom of a bag of im-
ported Cannabis.
Grade #6 - Parentage and origin are unknown.

why not just post this link?

Marijuana Botany An Advanced Study In Propagation & Breeding Of Marijuana: chapter 2

There is alot more good information there too.