Mendelian Genetics - E1

• Mendel used a model experimental approach to study patterns of inheritance
• Gregor Mendel:

  • born in 1822 in Austria
  • studied primarily mathematics and physics at the university of Vienna
  • he was an unaccredited teacher in Monastery
  • he developed his pea garden in Bruno, Czechoslovakia
  • in 1865, his pea results were reported to the Bruno society for natural science
  • in 1866, Mendel published Experiments on Plant Hybrids
• Gregor Mendel was the first person to understand the crossing of genetics with peas
• MENDEL'S GENETICS:

  • during 1868, he became an abbot (chief) of the monastery
  • he then spent the rest of his life in administrative work, and partying, etc.
  • Gregor Mendel died in 1884 (age 62)
  • in 1900, three scientists rediscovered Mendel's work and decided to call him the "father" of genetics
  • Carl Correns ~ Germany
  • Hugo de Vries ~ Netherlands
  • Erich von Tschermak ~ Austria
• Mendel used a model experimental approach to study patterns of inheritance
• Mendel chose his garden pea as a model system because:

  • easy to grow
  • it can grow to maturity in one season
  • it has true-breeding strains
  • it has observable characteristics with two distinct forms
  • it has controlled matings- self-fertilization or cross-fertilization
• there were seven contrasting traits that were noticeable throughout the Mendel's peas that helped him create his ideas of genetics
• seed shape - round and wrinkled - F1 results: all round

  seed color - yellow and green - F1 results: all yellow

  pod shape - full and constricted - F1 results: all full

  pod color - green and yellow - F1 results: all green

  flower color - violet and white - F1 results: all violet

  flower position - axial and terminal - F1 results: all axial

  stem height - tall and dwarf - F1 results: all tall
• during Mendel's lifetime, his work was unappreciated but after his death his results were rediscovered and appreciated
• Mendel's postulates were eventually accepted as the basis for Mendelian/ transmission genetics
• the monohybrid cross reveals how one trait is transmitted from generation to generation
• monohybrid crosses involve a single pair of contrasting traits
• the original parents are the P1 generation and their offspring are the F1 generation
• offsprings arise from self-fertilizing the F1 generation to the F2 generation
• monohybrid cross involves only ONE gene
• filial generation - first
• in the F1 generation of a monohybrid cross, all plants have JUST one of the two contrasting traits
• in the F2 generation, 3/4 of plants exhibit the same trait as the F1 generation

  1/4 exhibit the contrasting trait that disappeared in the F1 generation
• Mendel proposed the existence of "particulate unit factors" for every trait
• Mendel suggested that genes are passed unchanged from generation to generation that determines various traits expressed by each individual plant
• Mendel's monohybrid crosses were NOT sex dependent
• reciprocal cross example:

  it didn't matter whether a tall male plant pollinated a dwarf female plant or the other way around, the results were the same either way
• Mendel's three postulates of inheritance:

  • unit factors exist in pairs
  • one unit factor is dominant and the other is recessive
  • the paired unit factors separate independently during gamete formation
• the parental plants are the P generation

  their hybrid offsprings are the F1 generation

  a cross of the F1 plants form the F2 generation
• two alleles for a gene - one can make it grow tall or short (plant only not pure hybrid)
• both alleles are either tall or short (non-plant and pure hybrid)
• dwarf - homozygous
• gametes - haploid
• if the letter of the gene is capitalized, then it is dominant and will always be expressed, while small letters are recessive
• heterozygous individuals ~ both small and big letters - recessive and dominate
• inbreeding can NOT be done within humans and animals, plants only
• homozygous - same

  heterozygous - different
• phenotypic 3:1
• one of three Mendel's postulates in depth:

  unit factors in pairs:

  • genetic characters are controlled by unit factors existing in pairs in individual organisms
• one of three Mendel's postulates in depth:

  dominance and recessive:

  • dominance and recessive: in the pair of unit factors for a single characteristic in an individual, one unit factor is dominant and the other is recessive
• one of three Mendel's postulates in depth:

  segregation:

  • the paired unit factors separate independently during gamete formation
• reciprocal cross - bisexual plants
• R.C. Punnete created the Punnett square
• the punnett square allows the genotypes and phenotypes to be visualized
• genes are found in alternative versions called alleles