Anil Thapa Department of Horticulture Agriculture and Forestry University

1. Presented By
ANIL THAPA
Department of Horticulture
AFU, Rampur Campus
SEX DETERMINATION IN PAPAYA
AGRICULTURE AND FORESTRY UNIVERSITY
Rampur Campus

2. Introduction
Papaya (Carica papaya) belongs a small family with about
35 species.
 Papaya is diploid with 9 pairs of chromosomes (2n=18).
 Papaya is somewhat unusual in that it is trioecious with
three basic sex forms: male, female and hermaphrodite.
 But varieties are either dioecious or gynodioecious.
 Male trees are categorized by long, many flowers.
 Female trees have short inflorescence with few flowers,
have no stamens.
 Hermaphrodite papaya trees are primarily self-pollinated.

3. Male flowerFemale flower Hermaphrodite flower
Male fruit Female fruit

4. Objectives
To be acquainted with sex determination in papaya.
To know about different sex determining mechanism in
papaya.

5. Genetics of Sex
 Sex in papaya cannot be determined in seed or in juvenile
vegetative stage before flowering.
 But, sex ratio can be predicted in the progenies raised through
controlled pollination.
 32 heritable sex forms in papaya (Storey, 1958).
 Classified papaya flowers in 8 categories i.e.
 Staminate -by male plant
 Teratological staminate -by sex reversing male plants
 Reduced elongata
 Elongata
 Carpelloid elongata -by hermaphrodite plants
 Pentandria
 Carpelloid pentandria
 Pistillate -by female plants
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6.  Two sex determination genes control the sex determination
pathway of papaya.
 A feminizing or stamen suppressor gene,
 A masculinizing or carpel suppressor gene.
 Genetics of Papaya’s sex determination include;
A single gene with three alleles,
A group of closely linked genes,
A genic balance of sex chromosome,
Classical XY chromosomes,
Regulatory elements of the flower development pathway.

7. Single gene with three alleles
 Proposed by Hofmeyr (1938) and Storey (1941), based on the
segregation ratios from crosses among three sex types.
 Sex determination controlled by single gene with three alleles
named M, Mh and m.
 Male individuals(Mm) and hermaphrodite individuals (Mhm)
are heterozygous.
 Female individuals(mm) are homozygous recessive.
 Dominant combinations of MM, MhMh and MMh are lethal,
resulting in a 2:1 segregation.
 1:1 segregation of male to female or hermaphrodite to female
from cross pollinated female seeds.

8. Sex ratio of crosses between different sex
types:
Crosses Sex Ratio
Female(mm) Male(Mm) Hermaphrodite
(Mhm)
Lethal(MM,
MMh, MhMh)
Male selfed
(Mm×Mm)
1 2 0 1
Female×Male
(mm×Mm)
1 1 0 0
Hermaphrodite selfed
(Mhm×Mhm)
1 0 2 1
Female×Hermaphrodite
(mm×Mhm)
1 0 1 0
Male×Hermaphrodite
(Mm×Mhm)
1 1 1 1

9. Genic Balance Hypothesis
Proposed by Hofmeyr (1939), as an alternative hypothesis.
 Explained genic balance between sex chromosome and autosomes.
 Different sex types were the result of genic balance between the
sex chromosomes and autosomes.
 Chromosomes bearing M,Mh and m alleles are “sex
chromosome”. M and Mh represent an inactivated region of sex
chromosome where vital genes were eliminated. And ‘m’ sex
chromosome is present in each genotype that is viable.
 Female sex determining factors predominate the “sex
chromosomes” while the male sex determining factors are in the
autosome.

10. A group of closely linked genes controlling sex
determination:
 Modified hypothesis by Storey (1953), based on the observation
of flower peduncles.
 Suggested that lethal factor is associated only with male and
hermaphrodite homozygous dominant genotype.
 Based on Storey’s model, genotypes of male, hermaphrodite and
female were given as:
 Male: Mp/C+sg/+++sa+
 Hermaphrodite: +/C+sg/+++sa+
 Female: +++sa+/+++sa+
 The gene controlling long peduncle of male flowers i.e. Mp, Is the
only one that distinguishes the genotype of male flowers from
that of hermaphrodite flowers.

11. X and Y sex chromosome system
 Later, it was hypothesized only two sex types in papaya:
 Females
 Variable type that ranges from complete male to
hermaphrodite with numerous intermediate types in
between.
 The genotypes of male, female and hermaphrodite were XY, XX
and XY2 respectively.
 Suggested that the Y chromosome has a region containing a
lethal factor.
 And Y2 is a modified form of y chromosome but includes the
region of lethality.

12. Molecular genetics of sex determination
 Application of molecular techniques and biotechnology
has revolutionized the field of sex determination in
papaya. Some of these techniques include;
 Sex-linked DNA markers.
 Linkage mapping of sex determination locus.
 Fine mapping of sex determination locus
 Physical mapping of sex determination locus.
 Sample sequencing in the non-recombining region
 A primitive sex chromosome system

13. Current understanding of sex determination in
Papaya:
 Two genes are involved in sex determination in papaya:
 Feminizing gene for stamen abortion in female flowers.
 Masculinizing gene for carpel abortion in male flowers.
 Sex determination in papaya is controlled by a pair of sex
chromosome.
 There are two slightly different Y chromosome in papaya:
 Y for the male and
 Yh for hermaphrodite.
 At least two genes differentiate Y and Yh chromosomes:
 One gene controls the long peduncle on male trees.
 Masculinizing gene controls the carpel abortion in male flowers.
 Combination of the Y chromosomes YY, Yyh and YhYh would lead
to the same fate of embryo abortion.