| (27) |
In 1942, Kihara Institute for Biological
Research was established, where an important part of the research
was carried out. |
| (28) (29) |
(Field-working) |
| (30) (31) |
Crossing technique: castration or emasculation
of mother plant. |
| (32) (33) |
Two days later, pollination with pollen
from the anthers of the father. (34) |
| (35) |
In a little while after dusting the stigma
with pollen, |
| (36) |
the pollen tubes elongate and grow into
the stigma tissue until they reach the ovary. (37) |
| (38) |
In an intragroup hybrid, for instance
a tetraploid hybrid between two Emmer species, |
| (39) |
the homologous chromosomes from both parents
conjugate and 14 bivalents appear at metaphase, like in the parents.
Therefore, species which belong to one group, can be considered to
represent the same collective species. |
| (40) |
Now, let us describe a pentaploid hybrid
between Triticum polonicum and Spelta. |
| (41) |
When Emmer is pollinated with Dinkel pollen,
many shrivelled seeds are obtained. But germination is poor. |
| (42) |
On the other hand, when Dinkel is the mother, |
| (43) |
a small number of plump seeds are set.
Germination is good. |
| (44) |
In the somatic cells of the pentaploid
hybrid, 35 chromosomes are found, 14 belonging to Emmer and 21 to
Dinkel. |
| (45) |
(Microscopic observations) |
| (46) |
In the meiosis of the hybrid 14 bivalent
and 7 univalent chromosomes are observed. The bivalents belong to
the Emmer chromosome-sets A and B, which both parents have in common.
The univalents belong to another set of chromosomes, different from
A and B. We can see in detail the behavior of these chromosomes. |
| (47) |
The pollen mother cell turns slowly from
side view to polar view. Again the side view. |
| (48) |
The homologous chromosomes from both parents
conjugate in the prophase.
In the first metaphase 14 bivalents form the eqatorial plate, then
they divide and the daughter halves move toward the poles. Soon after
that the 7 univalents arrive at the equatorial plate and split longitudinally.
In the second division the 14 daughter chromosomes of the bivalents split
longitudinally, but the 7 halves of the univalents are distributed
at random to both poles, without further splitting. Therefore, gametes
with 14 to 21 chromosomes are formed. |
| (49) |
On the female side the embryosacs with
intermediate chromosome number are fertilized, while on the male side
14 and 21 chromosome pollen grains perform fertilization with much
higher frequency than those with intermediate chromosome numbers.
|
| (50) |
If both male and female gametes unite in
free combination, F2-plants must have chromosome numbers
ranging from 28 to 42. |