The document discusses hybridization of plants, comparing old and new techniques. It defines hybridization as interbreeding between different species or genetically divergent individuals of the same species. One of the first to study hybridization was Josef Kölrueter in 1760. New techniques like time course imaging allow observation of hybrids over generations. Hybridization can result in heterosis, transgressive segregation, adaptive introgression, and hybrid speciation, introducing new genetic variation and phenotypes. Both advantages like increased variability and resistance, and disadvantages like sterility can result.

1. HYBRIDIZATION OF PLANTS
OLD IDEAS, NEW TECHNIQUES
Group Members: Isidro Chan, Jordi Catzim, Hazael
Barrea
Presented to: Dr. Jorge Trejo
Course: Plant Physiology
Date: April 8th, 2019

2. OBJECTIVES:
• Students will learn about what it hybridization in
Plants
• Students will also be able to learn and differentiate
between old practices and new practices.
• Diagrams will be used to know of hybridization.
• Students will also learn about who was the first one
in using hybridization.
• Lastly, students will be able to answer some
questions pertaining the related topic.

3. INTRODUCTION
• Hybridization is the process of interbreeding between individuals of different
species (interspecific hybridization) or genetically divergent individuals from
the same species (intraspecific hybridization).
• One of the first persons to study plant hybridization was Josef Kölrueter,
who published the results of his experiments on tobacco in 1760.

4. EVOLUTIONARY CONSEQUENCES OF
HYBRIDIZATION
• Hybrids are often inviable, sterile, or exceedingly rare,
such that genetic exchange between species is not possible.
• Hybridization without gene flow has fewer evolutionary
consequences and, therefore, is not addressed here.
• Instead, we focus primarily on how hybridization with gene
flow affects the genetic and phenotypic composition of
populations immediately and over longer evolutionary
time scales.

5. HETEROSIS
Heterosis, hybrid vigor, or outbreeding enhancement, is the improved or increased
function of any biological quality in a hybrid offspring. An offspring is heterotic if its
traits are enhanced as a result of mixing the genetic contributions of its parents.
Dominance hypothesis. The dominance hypothesis
attributes the superiority of hybrids to the suppression
of undesirable recessive alleles from one parent by
dominant alleles from the other.
Over dominance hypothesis. Suggests that the heterozygous
genotype is superior to both homozygous genotype

6. Time course imaging of two maize inbreeds (LH198 and PHG47)
and the F1 hybrid (LH198/PHG47) generated by crossing the two together.

7. TRANSGRESSIVE SEGREGATION
Similar to heterosis, transgressive segregation occurs when phenotypic trait
values in hybrid populations fall outside the range of parental variation.
Transgressive segregation demonstrates how hybridization can produce
novel phenotypes and thus enable adaptation to new ecological niches
transgressive segregation is distinct from heterosis because it manifests predominantly
in the F2 generation and later and may persist indefinitely once established

8. • Factors that contribute to transgressive
segregation
Genetic
One cause can be due to recombination of additive alleles. Recombination results in
new pairs of alleles at two or more loci. These different pairs of alleles can give rise to
new phenotypes if gene expression has been changed at these loci.
Environmental
Environmental factors that cause transgressive segregation can be influenced by human
activity and climate change. Both human activity and climate change have the capability
to force species of a specific genome to interact with other species with different
genomes.

9. ADAPTIVE INTROGRESSION
Introgression, also known as introgressive hybridization, in genetics is the movement of a
gene (gene flow) from one species into the gene pool of another by the repeated
backcrossing of an interspecific hybrid with one of its parent species.
Excessive gene flow can lead to genetic swamping and the extinction of rare taxa
however, introgression also may serve as an evolutionarily creative force by introducing
new, possibly adaptive, genetic variation
into a population

10. • Example
Iris

11. HYBRID SPECIATION
Hybrid speciation is a form of speciation where hybridization between two different
species leads to a new species, reproductively isolated from the parent species.
Two species mate resulting in a fit hybrid that is unable to mate with members of its
parent species.

13. REINFORCEMENT
Reinforcement is a process of speciation where natural selection increases the reproductive
isolation between two populations of species. This occurs as a result of selection acting
against the production of hybrid individuals of low fitness.
Two incipient species evolve complete reproductive isolation due to selection rejecting unfit
hybrids. Here, mate discrimination acts to reinforce the speciation process.

14. A schematic description of the reinforcement process

15. Advantages
In general, hybrids exhibit new morphophysiological
characteristics obtained by genetic recombination
between the two crossed plants. These characteristics
can be:
• Changes in color, number and size of leaves, stems,
flowers, fruits and seeds. Greater variability
• Better resistance to specific pests and climatic
conditions not tolerated by type plants.
• Growth and accelerated multiplication.
• Some annual or biennial plants can become
perennials by obtaining more long-lived hybrids.
• Obtaining new species.

16. Disadvantages
• Hybrids will not always be obtained by the classical
method because many plants have mechanisms that
repulse pollen alien to their species.
• repression of flowering (never bloom),
• premature death,
• sterility (the hybrid will produce sterile flowers unable
to form viable seeds),
• hybrid breakage
• Many hybrids can become threats to the type
species, resulting in the extinction of these.

17. CONCLUSION
Our new challenge is to integrate advancements in
genomic and genetic techniques with classical experimental
protocols of genetic crosses, common garden field experiments,
and controlled environment manipulations to better understand
how and why hybridization has such important evolutionary
repercussions.

19. REFERENCES
• http://www.plantphysiol.org/content/plantphysiol/173/1/65.full.pdf
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5210733/
• http://www.plantphysiol.org/content/173/1/65