Prakash et al.

showed that because of high levels of heterozygosity most of the situation

represented a test cross and followed the 1:1 segregation in F ₁ progenies of

Douglas-fir. Besides, from theoretical considerations it would appear that lack of

co-dominance should not preclude the usefulness of the RAPD markers in genome

mapping studies with tree species (Allard, 1956).

Studies in analysis of segregation of RAPDs (Echt et al., 1992, Roy et al., 1992)

have put forth two assumptions concerning these markers: (1) each band is

considered to represent a single locus and is (2) a dominant marker for the locus.

On this basis, the presence of fragment in a parent is considered to be either in

the homozygous condition or in the heterozygous condition. It is not generally

possible to distinguish homozygosity from heterozygosity at a locus from the

presence of a RAPD band or marker. (Carlson et al., 1991). However, attempts can

be made to assign the genotype based on the marker status and its segregation in

progenies. Huang et al (2000) estimated the allelic frequency indirectly using the

homozygous null genotypes (-/-) and correlated for dominance according to Lynch

and Milligan (1994). An estimate can be made about the homo or heterozygotic

status of the RAPD locus based on the relative band intensity, which may not

be always accurate. A parent without the RAPD band is assigned the recessive

genotype. When a marker present in one parent but absent in the other ( Pp x pp or

pp x Pp ) the marker will segregate in 1:1 in the F ₁ generation. When a marker is

present in both the parents the parents ( Pp x Pp ) the expected segregation ratio for

that marker to the progeny is 3:1. In this study the data were analyzed within the

framework of these assumptions. Segregating 12 RAPD markers were considered

foranalysisofChi-squaretestswereperformedforeachofthemarkerstodetermine

the segregation difference from the expected ratio of 3:1 and 1:1. Out of the 12

RAPD loci observed in the parents 3 markers followed the segregation pattern of

3:1 and another 3 markers followed the segregation ratio of 1:1 at a significance

level of P=0.05. The deviation of other RAPD markers from Mendelian pattern

of inheritance may be attributed to the availability of limited progenies for the

study where no sampling strategy could be applied. Segregation analysis may

strictly follow the expected Mendelian pattern of inheritance. Similarly Mendelian

inheritance pattern of RAPD have been obtained in broccoli and cauliflower (Hu

and Quiros, 1991), Lettuce (Michelmore et al., 1991), tomato (Giovannoni et al.,

1991) and Betula (Roy et al., 1992).

In three progenies (namely, P ₃₇ , P ₄₀ and P 42 ) a new marker OPA-02 1200 not present

in either of the parents appeared. The probable reasons may be : (1) as a result

of recombination that produced new binding sites for the primers in the genomic

DNA of the F ₁ progeny, (2) imperfect matching and binding of the primers to

template DNA (William et al., 1990), Rafalski et al 1991). (3) Competition for the

primer-binding sites is an important factor controlling, which RAPD fragments

are sufficiently amplified to be visible.

36

Int. J. Bioinformatics and Biological Sci.: v.2 n.1&2, p. 23-39. March & June 2014