Q.63 A dioecious plant has XX sexual genotype for female and XY for male. After double fertilization,
what would be the genotype of the embryos and endosperms?
(A) 100% ovules will have XXX endosperm and XX embryo
(B) 100% ovules will have XXY endosperm and XY embryo
(C) 50% ovules will have XYY endosperm and XY embryo, while other 50% will have XXY
endosperm and YY embryo
(D) 50% ovules will have XXX endosperm and XX embryo, while the other 50% will have XXY
endosperm and XY embryo
In dioecious plants like papaya, where females are XX and males XY, double fertilization produces specific embryo and endosperm genotypes due to male gamete variation.
Double Fertilization Basics
Double fertilization in angiosperms involves one sperm fertilizing the egg (X from female) to form the diploid embryo, while the second sperm fuses with two polar nuclei (both X from female) to form triploid endosperm.
Male pollen delivers two sperm: 50% X-bearing and 50% Y-bearing, leading to varied outcomes across ovules.
Correct Answer: Option (D)
Option (D) states 50% ovules have XXX endosperm and XX embryo, while 50% have XXY endosperm and XY embryo, which matches the process precisely.
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When X-sperm fertilizes egg: embryo XX; remaining Y-sperm with XX polar nuclei gives XXY endosperm (50% chance).
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When Y-sperm fertilizes egg: embryo XY; remaining X-sperm with XX polar nuclei gives XXX endosperm (50% chance).
This 50-50 split reflects equal production of X and Y gametes from XY males.
Why Other Options Fail
Option (A): Claims 100% XXX endosperm and XX embryo, ignoring Y-sperm’s role in half the fertilizations.
Option (B): Suggests uniform XXY endosperm and XY embryo, but female gametes can’t produce YY embryos.
Option (C): Proposes XYY endosperm (impossible, as polar nuclei contribute XX) and YY embryo (not viable from X egg).
Each incorrect choice overlooks independent sperm function or female contribution.
