Genetics

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Genetics

• Genotype
• Mutations
• Genetic Improvements

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Genotype vs Phenotype

• genotype genetic makeup of an organism
• phenotype visible result of the interaction
  between genotype and environment
• heredity - ability to transmit information to
  offspring

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Plant Genotype

• Nucleus contains chromosomes
• DNAproteins
• DNA specific sequences - genetic code - Genes
• DNA - transcription produce RNA
• RNA translation - polypeptides/proteins

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Genome

• complete set of chromosomes
• constant within a species (1 to 500
  chromosomes)
• Human 46 (23 pairs)
• Porcupine 34
• Buffalo 60
• Lettuce 18
• Petunia 14

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Genome

• 1 set (n) monoploid
• 2n diploid - pairs of chromosomes
• homologous or heterzygous
• 3n or greater polyploid
• many of the polyploids are asexually propagated
• http//www.polyploidy.org/index.php/Main_Page
• Caused by doubling in mitosis or non-reductive
  meiosis

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Chromosome facts

• The record for minimum number of chromosomes
  belongs to a subspecies of the ant Myrmecia
  pilosula, in which females have a single pair of
  chromosomes. This species reproduces by a process
  called haplodiploidy, in which fertilized eggs
  (diploid) become females, while unfertilized eggs
  (haploid) develop into males. Hence, the males of
  this group of ants have, in each of their cells,
  a single chromosome.
• The record for maximum number of chromosomes is
  found in found in the fern family. Polyploidy is
  a common conduction in plants, but seemingly
  taken to its limits in the Ophioglossum
  reticulatum. This fern has roughly 630 pairs of
  chromosomes or 1260 chromosomes per cell. The
  fact that these cells can accurately segregate
  these enormous numbers of chromosomes during
  mitosis is truly remarkable.

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Genes Genetic Variability

• alleles or traits
• genes occupying same position on chromosomes
• position of gene locus
• Very important to know loci for genetic
  modification

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Genes Genetic Variability

• dominant allele/gene
• expressed whether plant is homozygous (RR)
• both alleles identical
• or heterozygous (Rr)
• two alleles are different
• recessive gene
• expressed only if both alleles are recessive (rr)

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Alleles

• D dominant allele for height, tall
• d recessive allele for height, dwarf
• Dd heterozygous - unlike alleles
• DD, dd homozygous - identical alleles

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Hybrids

• Seed color - Monohybrid
• Yellow Vs Green
• F Fillia
• F1, F2, F3
• Seed color and Seed coat - Dihybrid

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Hybrid

• parents with different genotype crossed

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Hybrid Vigor

• hybrid vigor - (concentration of favorable
  dominant genes)
• favorable genes of both parents expressed in
  progeny
• frequently expressed as increase in size or vigor
  relative to parents

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Hybrid Vigor - Heterosis
Inbred A AABBccddEE
Inbred B aabbCCDDEE
X
F1 Hybrid aAbBcCdDEE
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Genetic MutationCell Division Errors

• Mutations occur during meiosis or mitosis
• errors during replication and division
• altered genes may result in changes in
  characteristics
• Nongrafted plants that are composed of two
  genetically different parts
• The result of superior genetic changes can result
  in new cultivars

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Cell Division Errors

• bud sports - alteration in genetic makeup of
  single bud
• dark red delicious is result of bud sport
• ruby red grapefruit
• chimeras - a portion of shoot is genetically
  changed
• variegated leaf patterns
• thornless blackberry
• chimeras and bud sports are asexually propagated
  to maintain the new genotype

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Chimera
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Plant Improvement

• Selection from naturally occurring populations
• Breeding - planned sexual recombination
• Use genetic variability to produce plants with
  improved traits
• GMO
• Agrobacterium
• Bombardment