Biology Reference
In-Depth Information
sunflower RFLP map was published by the USDA sunflower research group
(Jan et al. 1998). This map had 271 marker loci detected by 232 cDNA probes
and covered 1,164 cM in 20 linkage groups. Two public inbred lines, HA
234 and RHA 271, were used for developing the F
2
mapping population.
There are obvious common features of these maps: 1) marker distribution
was not uniform throughout the genomes, 2) large gaps of more than 20 cM
existed in a few linkage groups, 3) distorted segregation was frequently
observed, and 4) a considerable proportion (30 to 35%) of the mapped loci
showed dominant segregation. From this, we could infer that the sunflower
genome has extensive duplication. Since there are few obvious conserved
linkage blocks among chromosomes, enormous reshuffling must have occurred
after the duplication. The common distorted segregation could have resulted
from selection against certain genotypes during gametogenesis, fertilization
(the existence of self-incompatibility), seed development germination and plant
growth. Some of these maps were used later for mapping a downy mildew
resistance gene (Mouzeyar et al. 1995; Roeckel-Drevet et al. 1996; Vear et al.
1997) and
Sclerotinia sclerotiorum
resistance QTL (Mestries et al. 1998), and for
identifying candidate-genes for downy mildew and
S
.
sclerotiorum
resistance
(Gentzbittel et al. 1998). Some of the mapped single or low-copy probes were
recently used to identify chromosome-specific bacterial artificial chromosome
(BAC) clones (Feng et al. 2006) and for assessing SNP frequencies, nucleotide
diversity, and linkage disequilibrium (LD) in modern cultivated sunflower
lines (Kolkman et al. 2007).
3.5.2 AFLP Maps
Peerbolte and Peleman (1996) applied AFLP to sunflower genome mapping.
They used 11 primer combinations on the DNA of 92 individuals from two
CARTISOL F
2
populations, CX x RHA 266 and PAC2 x RHA 266. Two
hundred forty-one (188 co-dominant) and 282 AFLP (243 co-dominant)
markers were mapped to the two populations, respectively. Using JoinMap,
the two maps were integrated in a combined map consisting of 437 markers
(146 RFLPs and 291 AFLPs) spread over 19 linkage groups (3 markers or
more) with a total length of 1,144 cM. Gedil et al. (2001) reported an integrated
RFLP-AFLP linkage map constructed from the 180 F
2
progeny derived from
two public sunflower lines, HA 370 and HA 372. This map consisted of 296
AFLP and 104 RFLP markers in 17 linkage groups and was 1,326 cM long.
They observed densely clustered AFLP markers on several linkage groups,
and presumably reside in centromeric regions. Since the RFLP probes were
mapped by Berry et al. (1995), 14 of 17 linkage groups of the two independent
RFLP maps were able to be aligned by common RFLP markers. Kusterer et
al. (2004) constructed a linkage map from 183 F
2
individuals from the cross
RHA 325 (cms) × HA 342. The map covered 1,751.5 cM with 202 AFLP and
Search WWH ::
Custom Search