- P generation: Parental generation, Mendel crossed a purebred purple with a purebred white plant
- People used to believe in blending inheritance: traits are mixed
- Ex: a tall person mates with short person = medium height baby
- F1 generation: created only purple plants, traits didn’t blend → proved blending inheritance wrong
- F2 generation: offspring produced by breeding F1 Generation; Mendel bred purple hybrids and created 75% purple and 25% white flowers
- Showed that traits do not blend together, can be hidden and come out in a later generation
- People used to believe in blending inheritance: traits are mixed
Types of Crosses
- Monohybrid cross: only one trait (ex: stem length)
- Dihybrid Cross: investigating two traits (Ex: stem length and flower color) [16 squares → use FOIL]
- For dihybrids, the ratio is D/D : D/r : r/D : r/r
- Testcross: find out the unknown allele that corresponds with the dominant phenotype of an organism
- Cross the dominant organism with a homozygous recessive organism, if any of their offspring are recessive, then the dominant organism is heterozygous (Bb)
Important Ratios
- 3:1 → Heterozygous x Heterozygous monohybrid cross
- 1:2:1 genotypic ratio
- 9:3:3:1 → dihybrid cross in which all alleles undergo independent assortment (unlinked)
- Heterozygous x Heterozygous
- 4:4:4:4 → Heterozygous x Homozygous dihybrid cross
Mendel’s Law of Inheritance
Law of Segregation
- Describes how alleles are segregated into different gametes and reunited after fertilization
- During anaphase I, homologs separate randomly to opposite poles so that each gamete only receives one copy of each allele
- Describes alleles of same gene
- Process in meiosis that ensures gametes get both maternal and paternal chromosomes
Mendel’s Law of Independent Assortment
- Every character is inherited on its own bcuz alleles of different genes randomly orient during metaphase I and are sorted independent of the other one.
- In other words, the allele a gamete receives for one gene does not influence the allele received for another gene
- Brown hair doesn’t mean you will get brown eyes
- The behavior of one homolog doesn’t affect that of another
- In other words, the allele a gamete receives for one gene does not influence the allele received for another gene
- Assumes every gene is found (or behave like they are) on different chromosomes and are not inherited together
Describes alleles of different genes