[5단원.생식과 유전]5-15.멘델의 유전 실험

Scientific concepts / discoveries / nature phenomena

Mendel’s heredity experiments (pea crossbreeding)

• Mendel crossed pea plants with contrasting traits (e.g., yellow vs. green, round vs. wrinkled).
• He examined the hybrids produced by crossing purebred lines, then tracked their offspring across generations.

Historical model being tested

• Before Mendel, it was commonly believed that parent traits blend like paint and are passed to offspring.
• Mendel questioned whether true blending occurs, and instead tested inheritance using controlled breeding.

Why peas are suitable for genetics

• Easy to grow and relatively resistant to pests/disease
• Short generation time: about 4 months (up to 8 months) from sowing to harvest
  • This makes it possible to observe multiple generations quickly
• Large number of offspring per cross → better statistical analysis
• Clearly distinct contrasting traits (e.g., seed shape and color)
• Ability to create purebred individuals via self-pollination

Pollination and breeding methods

• Pollination: pollen attaches to the stigma
• Self-pollination: pollen from a plant’s own stamen to its own stigma
• Cross-pollination: pollen from one plant’s stamen to a different plant’s stigma
• Mendel used repeated self-pollination to create purebred lines.

Purebred vs. hybrid

• Purebred: consistently produces offspring with the same traits after multiple self-pollination generations
• Hybrid: offspring from cross-pollination between purebreds with different contrasting traits

Dominance, recessiveness, and incomplete dominance

• Dominance/recessiveness: in hybrids, one trait is expressed while the other is not.
• Example mentioned:
  • Incomplete dominance: the phenotype can be intermediate
  • The subtitles describe this as a case where “Mendel’s law of dominance” may not apply well.

Mendel’s experimental results (seed shape example)

• Cross round (dominant) and wrinkled (recessive) purebreds
• F1 generation: hybrids show only one trait shape (round)
• F2 generation: offspring show an approximately 3:1 ratio
  • About 3 round : 1 wrinkled
• A numerical example is cited as roughly 5,474 : 1,856 (described as ~3:1).

Similar result with seed color

• Cross yellow and green pea purebreds
• F1 hybrids show yellow only → yellow is dominant
• F2 shows approximately 3 yellow : 1 green → green is recessive

Mendel’s hypothesized mechanism

• Each trait is determined by genetic factors:
  • A pair of factors exists for a trait
  • One factor is inherited from each parent
• If the alleles differ:
  • the dominant allele is expressed
  • the recessive allele is not
• Law of Separation (segregation):
  • During gamete formation, the pair of factors separates
  • Each gamete receives one factor, which is passed to offspring

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Methodology / steps outlined

1. Choose pea lines with contrasting traits.
2. Produce purebred plants through repeated self-pollination.
3. Perform cross-pollination between purebreds (e.g., round × wrinkled, yellow × green).
4. Grow offspring across generations:
   • F1: observe which trait appears
   • F2: self-cross F1 hybrids and count offspring phenotypes
5. Compare phenotype counts to infer ratios (notably ~3:1).
6. Form hypotheses about:
   • inheritance by genetic factors
   • dominance/recessiveness
   • segregation of factor pairs into gametes

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Researchers / sources featured

• Gregory Mendel (1822–1884)
  • (No other specific researchers or sources are named in the subtitles.)