The study investigated the genetic control of apomixis in two Hieracium species. Crosses were performed between apomictic and sexual biotypes to generate hybrids. Segregation analysis of the hybrids found that apomixis behaved as a monogenic, dominant trait controlled by a single locus. Backcrosses determined that the homozygous recessive phenotype was sexuality. A second cross combining the two apomictic parents found that the dominant factors controlling apomixis in each were closely linked or allelic. The research demonstrated that apomixis can be inherited in polyploids through sexual or apomictic gametes carrying the dominant allele.

1. Heredity 84 (2000) 228-237

2. Data Analysis
and Results
Experimental
Design and
Data Collection
Organism

3. asexual formation of seed (genetically uniform progeny), yet the genetic mechanisms
that control this trait remain unclear
Megaspore mother cell
• Embryo sac = n
• Normal fertilization
• Somatic embryo (2n)
from nucellus replaces
sexual embryo
• Take over the
endosperm (=
pseudogamous)
• Facultative mechanism
– Either sexual or
asexual seeds are
formed
Diplospory
Adventitious embryony
Normal meiosis
Apospory
• A normal (n) embryo
sac
• Another diploid
embryo sac may
develop from a
nucellus cell
• Both develop
endosperms following
fertilization
(pseudogamous)
• Poly-embryony
• A facultative
mechanism
n
Normal meiosis
Non-reduction division
2n n
• No fertilization (2n egg
develops in an embryo)
• Non-pseudogamous
(autonomous) endosperm
development (from polar
nuclei)
• Meiotic diplospory/
mitotic diplospory
2n
nucellus

4. The trait is inherited through a single dominant gene
The Trait can pass through the diploid and haploid male gametes
Gametophytic apomixis is asociated with polyploidy

5. Data Analysis
and Results
Experimental
Design and
Data Collection
Organism

6. Two apomictic species of Hieracium with two different forms of mega-gametogenesis.
H. aurantiacum H. piloselloides H. pilosella

7. Two apomictic biotypes of Hieracium were used,
1- Triploid accession (2n=27, x=9) of H. piloselloides (designated `D3')
2- Aneuploid accession (2n=3x+4=31) of H. aurantiacum (designated `A3.4').
Both produce high degree of fertile haploid pollen
How can we detect that hybrid is success …!
Morphological markers (traits)…
1- bright orange flowers of H. aurantiacum
2- upright form and strap-shaped leaves of H. piloselloides
Two sexual biotypes were used;
1- Tetraploid accession of H. pilosella from Caen, France (designated `P4')
2- Anther culture-derived diploid (Bicknell & Borst, 1996) of P4 (designated `P2')
Both P4 and P2 appear to be self-incompatible under cool winter conditions

8. If embryos were detected the plant was scored as a putative apomict.
If embryos were absent but embryo sacs were present normally , the plant was
scored as sexual.
If degenerate structures were seen the plant was scored as sterile.
If flowers either failed to form or developed abnormally. These plants were also
scored as sterile.

9. Apomixis was defined as the formation of an embryo(s) at petal senescence following
the decapitation of an immature capitulum.
In apomictic biotypes of Hieracium maternal
embryos arise spontaneously before the final
senescence of the flower (stage 10 in
Koltunow et al., 1998).
•In sexual types, prevention of fertilization by
bud decapitation (Koltunowetal.,1995) leads to
the retention of aquiescent mature embryo sac
up until this developmental stage, so that
differences between sexual and apomictic types
could be readily determined
This measure is a score of parthenogenesis rather than apomixis as a whole as it
does not include a measure of meiosis.

10. chi-squared test for a fixed ratio hypothesis with application of the Yates's continuity
correction factor to compensate for the low number of observations in some data
sets.
S F
A a b NA
B c d NB
NS NF N
For a 2 × 2 table with the following entries:
some cases, this is better.
Yates corrections for continuity to testing for independence in a contingency table

11. Data Analysis
and Results
Experimental
Design and
Data Collection
Organism

12. To avoid apomixis
difficulties
crosses were
designed using
the apomict as
the staminate
parent and the
sexual plant as
the recipient.

13. The triploid progeny (3x) resulted from
the union of a haploid gamete from the
pistillate parent, with a diploid gamete
from the staminate parent.
Since, no plants were obtained with a
chromosome number greater than 27, it
appears that completely unreduced
gametes did not contribute to the
formation of this population.
Backcrosses were conducted to determine
which F1 category class (3x -apo, or 3x- sex.)
represented the homozygous recessive.
The 2 (2x) were sterile, whereas the 30 (3x)
BC1 plants segregated for apomixis similar to
the F1 population
BC of (3x) sexual F1 plant to the sexual parent
yielded only sexual progeny
Sexuality looks to be the phenotype of the homozygous recessive genotype

14. Poor recovery of (2x) in the cross (D3 and P2), shows a bias against survival of products
following the involvement of haploid, male gametes.
Q: Is it occur at the level of haploid gamete viability/efficacy, or of (2x) zygote
survival.
A: a cross (P4 and D3) was made …
The (2x) P2 was originally derived by anther culture from P4, so the P2 genome
represented a subset of P4. So that
The (3x) in this cross should be union of a (2x) egg (from P4) with
a (1x) sperm nucleus (from D3)

16. Apomixis segregated among both the (3x) and
(4x) F1 progeny.
Χ2 test consisted with the expected ratio and
proposed that (1x) gametes could transmit the
dominant allele conferring apomixis in this
system
The apomictic F1 BC resulted in a segregating
population, with ratios of apomictic and
sexual biotypes similar to the F1.
While the sexual F1 BC resulted in
only sexual and sterile progeny.

17. To test allelism it was necessary to combine the 2
dominant alleles in a single plant by crossing, also
one of the apomicts used as a recipient parent
Of the 10 hybrids, 4 were (4x), 4 were (3x) and 2 were
aneuploids ( 3x+4 and 3x+5). All were either apomictic
or sterile.
2 of the (4x), set many germinable seeds. The best of these
plants, designated `AD4', was test-crossed to the sexual (2x)
P2 and the (3x) progeny scored for apomixis.
Which means …
that sterility does not appear to be
preferentially associated with either apomixis
or sexuality.
However, close linkage, possibly allelism, is
indicated as the most probable genetic model.

18. Authors used hybridization between parents and also back crosses in their experiment
The research paper could be used as one of the applications for polyploidies, to
study genetics, and in this specific case, segregating progenies of apomixis.
Back crosses were used to test for inheritance of the dominant alleles in polyploidy
Apospory in H. piloselloides and H. aurantiacum was inherited as a monogenic,
dominant trait.
Both D3 and A3.4 were simplex for the dominant allele at the Apo locus.
Sexuality is the homozygous, recessive phenotype, which will lead to the dispersion
of dominant alleles.
The identification of 2 polyploids each bearing a single dominant allele at Apo locus
is consistent with the expectation arise rarely in this taxon.
The dominant factors of A3.4 and D3 are closely linked

19. Terms used in this presentation
Pistillate
Staminate
Ideotype
Back crosses
Test crosses
Biotypes
Apomixis
Triploid
Aneuploidy