Molecular Plant Breeding 2016, Vol.7, No.28, 1
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to four months from germination (Ma et al., 2004). If the prediction of sex of papaya could be done at early
seedling stage, then an expected male and female plants ratios (5% males: 95% females) would be maintained by
removing excess male trees. This would save the resources such as space required for planting, fertilizers, water
and labor etc. otherwise spent on these undesirable male trees. Prediction of papaya sex at seedling stage using
morphological traits have been attempted by many researchers but success began to achieved with advancements
in genomics, molecular tools and techniques. In this paper we have reviewed the genetics of sex determination
and highlighted on several methods including morphological, cytological or isozyme and molecular markers based
techniques for sex determination in papaya.
Figure 2 Sex determination mechanism in papaya (Idea taken from Heikrujam M, Sharma K, Prasad M, Agrawal V, 2015. Review on
different mechanisms of sex determination and sex-linked molecular markers in dioecious crops: a current update. Euphytica,
201:161-194)
3 Molecular Genetics of Sex Chromosomes in Papaya
In papaya, females possess homogametic X chromosome (XX), while male and hermaphrodite have heterogametic
XY and XY
h
chromosomes, respectively. The sex inheritance in papaya depends on three alleles including a
recessive “m” allele for females and a dominant “M” allele for males and “M
h
” allele for hermaphrodites. Female
(homozygous recessive; mm), male (heterozygous dominant; Mm) and hermaphrodite (heterozygous dominant;
M
h
m) are the three viable genotypes (Figure 2). The dominant homozygous combinations (M
h
M
h
, M
h
M, and MM)
would be lethal and therefore non-viable (Hofmeyr, 1967). It was assumed that dominant alleles M and M
h
represent genetically inactive regions of “sex chromosomes” which slightly vary in their length and functional
genes are lost in these regions. Therefore, these homozygous dominant genotype would be lethal, while Mm and
