Clonal Selection

Question 1

Bud-Sport

(Bud Mutation)

Answer 1

• when a mutant suddenly appears in the branch of a plant
• Sports are generally unwanted, but have been the source of many new cultivars
• a sudden change in a single branch due to a mutation apparently arising from a single bud

Question 2

Chimera

Answer 2

• A plant composed of a mixture of two genotypes, each expressed independently in separate layers of the shoot
• the different genotypes originate within the meristematic tissue

Question 3

Environment by Genotype Interactions

Answer 3

• a source of phenotypic variation
• clones gron in different environments may look different
• plant size, shape, flower number and color may all be different in plants grown in the sun versus in the shade

Question 4

Genetic Mosaics

Answer 4

• a source of phenotypic variation
• permanent genetic variation
• 4 ways:

1. variegation - the cellular-based cotrasting genetic expression in different parts of the same organ, usually caused by chimeras
2. patterend genes - a differential gene expression that is not due to cell arrangement
3. transposons - a unique kind of genetic element in cells of some organisms that have the capacity to change position within the chromosome
4. somaclonal variation - pathogens that infect the cells of a plant and spread throughout the plant, where they remain infective

Question 5

Genetic Variation

Answer 5

• one type of clonal variation (phenotypic variation is the other)
• Mutation - a permanent gentic change involving some part of the DNA molecule
• Bud-Sport - a sudden change in a single branch due to a mutation apparently arising from a single bud
• plants or seeds can be treated with chemicals or radiation to induce mutations

Question 6

Graft Chimera

Answer 6

• a chimera sometimes created when an adventitious shoot emerges from callus at a graft that has tissues of both the stock and scion

Question 7

Mericlinal Chimeral

Answer 7

• the mutant cells are only in a part of a single cell layer
• unstable
• thought of as a transition as cells divide to form a periclinal chimera or revert to a non-mutant form

Question 8

Monoculture

Answer 8

• the mass production of a single genotype within a singl planting
• since all the plants of a nursery, field orchard, or plantationhave the same genotype, each is equally vulerable to specific environmental hazards and specific pests and diseases and may lead to an overall loss of genetic diversity

Question 9

Patterned Genes for Variegation

Answer 9

• a differential gene expression (as a color pattern) that is not due to cell arrangement
• a genetic trait of the cultivar
• an inherited trait
• can be fixed by selection and seed propagation
• the pattern is different due to different cells in a tissue expressing color genes
• their typical pattern is displayed throughout the clone and expressed by each plant
• not a chimera

Question 10

Periclinal Chimera

Answer 10

• all the cells in one layer different from the other layers
• the most stable chimera
• common cause of leaf veriegation

Question 11

Phenotypic Variation

Answer 11

• one type of clonal variation (genetic variation is the other)
• involves a change in the way a plant’s genes are expressed
• is not a mutation
• sources of phenotypic variation:

1. environment by genotypic interactions (phenological changes)
2. ontogenetic aging (phase changes)
3. permanent genetic variation
4. infection by systemic pathogens (particularly viruses and similar organisms)

Question 12

Reversion

Answer 12

• a shoot which emerges from inner tissue of a chimera and shows the genotype of the inner tissue

Question 13

Sectorial Chimera

Answer 13

• the mutated tissue occupies a sector that encompasses all layers
• not stable
• would revert to a periclinal chimera or an all- mutant or non-mutant meristem
• an unusual chimera

Question 14

Systemic Pathogen Infection

Answer 14

• usually infection of a plant with a pathogen causes sever symptoms and can lead to plant death
• however, some viral infection cause only limited vigor loss
• n some cases they cause a variegated leaf or flower cover and are prepuated during propagation

Question 15

Transposon

Answer 15

• a moveable genetic element
• also called jumping genes
• they randomly move about the chromosome creating genetic mosaics
• A mobile genetic factor or jumping gene that turns on or off a gene resulting in a new phenotype
• the variegation pattern is inherited from seed (chimera not inherited from seed)

Question 16

Tunica-Corpus

Answer 16

.

Question 17

Advantage of Clones as Cultivars

Answer 17

• genetic improvement and selections
• uniformity of populations
• control of phases of plant development (ex. earlier bearing of fruit trees)
• combine more than one genotype into a single plant (grafting)
• greater commercial value
• facilitating propagation (sometimes only means to propagate)

Question 18

Disadvantages of Clones as Cultivars:

Answer 18

• monoculture
• slow reproductive rate
• lack of genetic variation for breeding and selection
• potential for propagating systemic pathogens from clonal sources
• insufficient genetic diversity for resistance against unforeseen pests or pathogens
• potential for latent genetic mutation

Question 19

Anticlinal Division

Answer 19

• the direction of cell division in an end-to-end position to produce a continuous payer
• (perpendicular to the surface)
• divisions that eventually become the epidermis and outer layers of the plant

Question 20

Periclinal Division

Answer 20

• the direction of cell division in a side-to-side position to increase numbers of cell layers
• (parallel to the surface)
• divisions to expand the shoot, particularly in the locations farther from the tip