Plant reproductive system Flashcards
(25 cards)
Factors affecting the development of varieties
-Reproductive system
-Ploidy level (diploid or polyploid)
- Inheritance model ( disomic or polysomic)
Modes of vegetative propogation
-Rhizombes
-Tubers
-Tillers
- Bulbs
-Cuttings
Sporophytic apomixis
the embryo develops directly from a diploid somatic cell (not from the egg cell), and without fertilization
Gametophytic apomixis
The embryos derives from an
apomeiotic (2n) egg formed within
an unreduced embryo sac (diplospory, apospory)
Diplospory
The embryo sac comes from a megaspore mother cell directly by mitosis (meiosis skipped→apomeiosis)
apospory
the embryo sac (female gametophyte) is formed from a somatic cell of the nucellular tissue.
Endosperm fertilization may be either
required (pseudogamy) or not required
(autonomous apomixis, rare)
Advantages of autogamy
-Ensures seed set in the abscence of pollinators
-Overcomes sterility
- Selectively advantageous by transmitting
both sets of genes to offspring, so well adapted genes are preserved
-
Disadvantages of autogamy
- decrease genetic variability
- Inability to adapt to changing conditions
- increase inbreeding depression (increase homozygosity of deleterious genes)
Cleistogamy
Flowers are not able to open
and are only capable of selffertilization in buds or spikelets
Self-Incompatibility
mechanism in Angiosperms that
prevents inbreeding and promotes outcrossing
How does self-incompatibility work
Involves a biochemical recognition in the
stigma/style (transmitting tissue) to reject self-pollen and prevent pollen grain germination
or pollen tube growth up to the ovary/ovules
Genetically controlled by S-locus
Gametophytic self-incompatibility (GSI)
The haploid of pollen
grain (gametophyte)
determines what matings
will be successful. RNases are enzyme that rejects pollen with the same S-allele.
Sporophyric self-incompatibility (SSI)
Pollen fertilization determined by the genotype of the parent plant (the sporophyte) that produced it.
Advantages of self-incompatibility
-Prevents selfing and expression of
deleterious genes
-Reduces inbreeding depression
-Increases genetic exchange (gene flow)
and hence genetic diversity
-Populations have the ability to adapt to
changing conditions
Disadvantages of self-incompatibility
Relies on effective
cross-pollination and seed dispersal
Male sterility
-Inability of plants to produce or to release functional pollen grains
-Controlled by nuclear or mitochondrial genes that affect meiosis, gametogenesis, or anther development.
-widely used in plant breeding for the
development of F1 hybrid varieties
Types of Male Sterility
nuclear male sterile
- Cytoplasmic male sterility (Controlled by mitochondrial gene with maternal inheritance)
- Cytoplasmic male sterility with nuclear restores
monoecy
-Hermaphrodytes
- Common in wind-pollinated plants
-common in temperate regions
-Self-pollination possible but not likely
Dioecy
-either male or female
- Common in tropical regions and oceanic islands
- Generally small flower size
- Always outcrossing, but inefficient
Protandry
Anthers release pollen before stigma receptive
Protogyny
Stigma receptive
before pollen release
Apomeiosis
meiosis is either absent or incomplete,
leading to the formation of unreduced
embryo-sac
Parthenogenesis
embryo develops from an unfertilized egg,
without genetic contribution from a male gamete
Autonomous endosperm development
formation of endosperm without fertilization of the central cell in the
embryo sac.
