Mechanism of sex determination in plants

i) Environmental: eg: melons, cucumber

• Temperature day length , ethylene, GA₃ , ions (Ca++, Mg++) affects the sex expression.
• Treatment of GA₃ or ethylene promotes the production of female flowers.

ii) Monogenic/genic: Papaya, Asparagus, Spinach, etc.

• Sex determination is determined by a single gene.
• In Papaya, single gene with 3 alleles (m, m1 and m2) controls the sex determination.
• (mm: female, m₁m: male and m₂m: hermaphrodite)
• Genotype m₁m₂ recessive lethal and non-viable (m₁ and m₂ alleles are recessive lethal)
• Genotypes m₁m₂ and m₂m₂ are non-viable.
• Conversion of maize plants into male and female plants by two recessive genes ba and ts is presented below:

iii) Chromosomal:

• In plant, the following chromosomal sex determination maechanism are found.

a) XX female XY male: This mechanism is found in Cannabis, Salix, Silene, Rumex, Bryonia and Humulux. Female has 2x chromosome but male has one X and Y chromosome. Random union between male and female gamete produces two types of zygotes: 50% of the zygote are XX and give rise to female plant, while the remaining 50% zygotes are XY and produce male plants.

• XX develops into female and XY develops into male.
• The Y chromosome of Silene is the largest chromosome of its complement. It has four functionally distinct segments:

Roles of different segments:

i) First segment: A deletion of this segment gives rise to hermaphrodite flowers on XY plants.

ii) Second segment: A deletion of this segment gives rise to female flowers on XY plants.

iii) Third segment: A deletion of this segment Produces male sterile plants with abortive anthers.

iv) Fourth segment: Homologous to a segment of an X chromosome.

v) Fifth segment of X chromosome: Development of female reproductive organs.

b)XY female XX male: Found in Fragraris.

c) XX female XY₁Y₂ male: Found in Rumex, Humulux. Reunion between male and female produces two types of zygotes of male and female respectively.

d) XX female XO male: Found in Dioscorea and vassisneria.