Principles Module 39
Inheritance Before Mendel
- blending: traits of parents would combine in offspring
- experience-dependent: traits modified through life, modified version passed to offspring
- used garden pea as model organism
- identified and followed true breeding traits, meaning those that were uniform among offspring
- garden peas will self-pollinate naturally, but can also be manipulated to prevent this and forced to cross-pollinate
- quantified the results of hundreds of crosses through many generations
Summary of Observations
- crossing true-breeding plants produced only 1 trait of the 2 in first generation
- crossing parent with green seeds with those having yellow seeds gave offspring with all yellow seeds
- the ‘missing’ trait would reappear in the second generation
- the offspring of the first generation produced mostly yellow-bearing seeds, but some with green seeds
- the reappearance of a missing trait disproved the other mechanisms of inheritance and led to Mendel’s theory of inheritance
Principle of Segregation
- each offspring receives 2 alleles, 1 from each parent
- the process of the 2 alleles separating during gamete formation leads to each gamete receiving only 1 of the alleles
- one of the alleles tends to mask the other, acting in a dominant manner
- the other, recessive allele, is latent but not gone or blended out
Questions for Practice
- Be able to provide a definition for each of the vocabulary terms.
- Provide an example result that demonstrates the principle of segregation.
- Why did Mendel choose pea plants as a model system? What were the benefits of this organism for the study of genetics?