modes of reproduction and apomixis Sexual reproduction asexual reproduction

1. Modes of Reproduction
• Reproduction refers to the process by which living
organisms give rise to the offspring of similar kind
(species)
• mode of reproduction is of two types: viz.
1)sexual reproduction and
2)asexual reproduction
• help in deciding the breeding procedures to be
used for the genetic improvement

2. Sexual reproduction
• Embryos which have developed by fusion of
male and female gametes
• Sporogenesis : Production of microspores and
megaspores
• Microsporogenesis : sporophytic cells in the
pollen sacs of anther which undergo meiotic
division to form haploid i.e., microspore

4. Megasporogenesis
• A single sporophytic cell inside the ovule, which undergo
meiotic division to form haploid megaspore, is called
megaspore mother cell (MMC)
• Each MMC produces four megaspores out of which three
degenerate resulting in a single functional megaspore

6. Gametogenesis
• The production of male and female gametes in
the microspores and megaspores
• Microgametogenesis: production of male
gametes or sperm
• Megagametogenesis : The development of
embryo sac from a megaspore
• Fertilization : The fusion of one of the two
sperms with the egg cell producing a diploid
zygote

7. • Animation

8. Asexual reproduction
• Multiplication of plants without the fusion of male and
female gametes
A) Vegetative reproduction – Natural and Artificial
B) Apomixis :
- “Apo” (Away from) "mixis" (act of mixing )
- Development of seed without sexual fusion (fertilization)
- obligate apomixis
- facultative apomixis

9. Reproductive Behavior
• Obligate Apomict: a plant which reproduces only by
asexual reproduction.
• Facultative Apomict: a plant which has the potential
to reproduce either sexually or asexually. Both
process may occur simultaneously or one may be
predominant.
• Within a genus or species, all reproduction strategies
may be possible

10. Apomixis
• Leuwenhock (1719) in Citrus seeds.
• More than 300 species belonging to 35 families
are apomictic

11. Apomixis
• Must bypass two different processes:
• Meiosis: no reduction of chromosome #
• Fertilization: development of embryo w/o fusion of sperm
and egg

12. Types of apomixis
• Adventive embryony. The development of
embryo directly from the diploid cells of ovule
lying outside the embryosac
- nucellus or integuments

13. Gametophytic Apomixis
• Apospory: Some vegetative cells of ovule develop
into unreduced embryosac
• Diplosopry : Embryosac is produced from
megaspore, which remains diploid
- Parthenogenesis: Development of embryo from
the egg cell without pollination
- Pseudogamy: The origin of embryo from either
synergids or antipodal cells of the embryosac,
pollination is required for endosperm

14. Genetics of Apomicts
• Apomixis is genetically controlled in most of cases
studied
• Control is complex (multigenic) and recessive to
sexual reproduction
• Polyploidy may affect apomictic reproduction
• Hybridization tends to increase apomixis

15. Use of Apomixis in Breeding
• Production of exact replicas of diploid
• Fix hybrid vigor
• Fix heterozygous status
• Efficient exploitation of maternal effect

16. Consequences of reproductive
mode
• a major factor driving its genome evolution
• Asexuality are associated with lower effective
recombination levels and smaller effective population
sizes
• As a result of reduced levels of diversity, selfers and
asexuals may be less adaptive to changing environment
• Also result in the accumulation of deleterious mutations
and other genomic changes

17. Significance of Vegetative
Reproduction
• A desirable plant may be used as a variety
directly regardless of whether it is
homozygous or heterozygous
• Mutant buds, branches or seedlings, if
desirable, can be multiplied and directly used
as varieties

18. Significance of Sexual
Reproduction
• Possible to combine genes from two parents
into a single hybrid plant
• Recombination of these genes produces a large
number of genotypes.