1. Asexual reproduction and plants that cover the reproductive bases

2. Asexual Reproduction + = + = N n NN Nn nn + = + =
Note: At this point in the figure, the antipodals and synergids are deleted and only the
fertilized endosperm nuclei (now 3n) and fertilized egg (now 2n) are shown. Only the fertilized
egg is carried to the Punnett square.

3. Asexual reproduction: The clone is immortal
Example #1: Allium sativum
“As far as we know, garlic in cultivation throughout history has only been propagated asexually by way of vegetative cloves, bulbs, and bulbils (or topsets), not from seed. These asexually propagated, genetically distinct selections of garlic we cultivate are more generally called "clones". Yet this asexual lifestyle of cultivated garlic forgoes the possibility of combining traits proffered by interpollinating diverse parental stocks.”

4. Asexual reproduction: The clone is immortal
But what if you want to change it?
Perspectives on breeding garlic
Induced mutation
Transgenics
Gene editing
Restore sexual fertility

5. Asexual reproduction: The clone is immortal
Example #2: Populus tremuloides Pando clone
The world's heaviest living thing: 6 million kilograms
47,000 genetically identical ramets
Aspen is dioecious species - this clone is one big male
One of the world’s most ancient organisms (?)
Threatened!

6. Red Delicious x Virginia Ralls Janet
Asexual reproduction: somatic mutations plus
sexual reproduction option
Delicious
1881
Red Delicious
1880 somatic mutation in Delicious
Many subsequent mutations selected
Fuji
Red Delicious x Virginia Ralls Janet
1930s

7. A transition to Apomixis+ = n
n n
N N N
N N
N N n
N n + = N
N N
N N N N n NN Nn nn + = N
N N
n n n
n n
n n N
n N + = n
n n
n n n
Note: At this point in the figure, the antipodals and synergids are deleted and only the
fertilized endosperm nuclei (now 3n) and fertilized egg (now 2n) are shown. Only the fertilized
egg is carried to the Punnett square.

8. Seeds without sex: Apomixis
Apomixis = parthenogenesis: Development of an egg without fertilization
(Parthenocarpy = development of fruits (seedless) without fertilization)
Allows for seed propagation of heterozygotes: genetically identical from generation to generation.
Obligate
Facultative 

9. Seeds without sex: Apomixis
Prevalence 400 species; 40 families; Common in Poaceae, Asteraceae, Rosaceae
Examples
Tripsacum
Poa pratensis
Pennisetum
Dandelion (Taraxacum spp)
Rubus

10. Seeds without sex: Apomixis
Mechanisms
No (or altered) meiosis to produce unreduced (2n) female gametophyte (embryo sac)
Autonomous embryo formation without fertilization, or
Endosperm development may be triggered by fertilization. (pseudogamy = fertilization of central cell but not egg)  

11. Seeds without sex: Apomixis
Hand and Koltunow Genetics 197:

12. Seeds without sex: Apomixis
Genetic basis
Apomixis loci and candidate genes
Lots of breeding effort; little success
Epigenetics?
“Our results highlight the potential of heritable DNA methylation variation to contribute to population differentiation along ecological gradients.” Preite et al

13. Seeds without sex: Apomixis
Economic implications of apomixis
Hybrid seed production? 
Transgenic apomict escape?
Evolutionary implications of apomixis
Obligate
Facultative

14. Covering the bases: asexual reproduction + apomixes + sexual reproduction= n
n n
N N N
N N
N N n
N n + = N
N N
N N N N n NN Nn nn + = N
N N
n n n
n n
n n N
n N + = n
n n
n n n
Note: At this point in the figure, the antipodals and synergids are deleted and only the
fertilized endosperm nuclei (now 3n) and fertilized egg (now 2n) are shown. Only the fertilized
egg is carried to the Punnett square.

15. Two plants that cover the reproduction and seed bases: Citrus and the Himalayan blackberry
Center of origin: Southeast Asia
Subsequent selection and diversification
Genome formula and size:
Most cultivated forms are 2n = 2x = 18
~ 400 – 600 Mb
Traits of economic importance: nutrition, flavor, aroma
Cool facts: The genus covers the reproductive bases.
Sexual forms as well as facultative and obligate apomicts.
Male and female sterility are common.
Parthenocarpy is a common feature.
Asexual propagation is common.
Selection of somatic mutants has led to much of the diversity we see and eat today.

16. Citrus: The family tree

17. Citrus – more insights:
Pummelo, citron, and some mandarin ancestors: obligate sexual reproduction
No apomixis
High genetic diversity
Orange, grapefruit, lemon satsuma, clementine:
Bud sport selections
Apomixis (nucellar embryony)
Maternal sporophyte tissue
Often polyembryonic seeds
Lower genetic diversity

18. Citrus – more insights:
Grapefruit: Spontaneous hybrid of pummelo and sweet orange.
Selection for seedlessness and pigment
Tangelo: Intentional cross of grapefruit x mandarin
Selection for seedless-ness, pigment, and flavor
Tahiti lime: Seedless triploid from 2x X 4x cross

19. Rubus armeniacus: The Himalayan (Armenian) blackberry
Center of origin: Armenia/Iran
Introduced to Europe and North America in 19th century
Rubus spp.
Genome formula and size: 2x – 18x; Mbp
Traits of economic importance: Invasiveness, delicious fruit, habitat
Cool facts:
The perfect weed?
Thanks to Luther Burbank

20. Is the Himalayan blackberry the perfect weed?
Attribute
Description
Flower
Hermaphroditic
Pollination biology
Self and outcross
Apomixis
Facultative
Seeds
Small and numerous
Vegetative propagation
Yes
Ploidy level
4x(?)
Protection
Thorns
Attraction
Tasty fruit
Was Luther Burbank the “father” of this
“perfect weed”?
“Himalayan Giant” for sale in his catalog in 1894
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