Monohybrid Cross Setup

Character: flower color
Traits: purple or white flowers
Mendel began by producing true-breeding plants.
- These, when crossed with their own color, will always produce the same color.
- Pure purple flowers
- Pure white flowers

The Results of the Cross

Crossing the true-breeds, Mendel got an interesting result in the F₁ generation: all purple.
Crossing these purples, he got another interesting result in the F₂ generation: ¾ purple, ¼ white.

Figure 14.2, page 241, Campbell's Biology, 5th Edition

There was a gene for flower color.
- This gene came in two alleles (versions): purple and white.
- These alleles reside on homologous chromosomes.
Each organism inherits two alleles, one from each parent.
One allele is dominant, and one is recessive.
- The dominant is always expressed in the offspring.
- The recessive is expressed if and only if there is no dominant allele present.
- In this case, the purple is dominant and the white recessive.
The two alleles for each character segregate during the production of gametes: Mendel's Law of Segregation.

Figure 14.3, page 241, Campbell's Biology, 5th Edition

The parental generation produce only one kind of gamete each.
The F₁ generation has their gametes “segregate”—therefore they produce 50 % P and 50 % p.
A Punnett square is used to find result of crossing individuals.

Figure 14.4, page 242, Campbell's Biology, 5th Edition

Note that the ratios of genotypes and phenotypes are different; we usually talk about the phenotype ratio (3:1 in the example cross).

Used to find out the true genetic makeup (genotype) of an individual with the dominant phenotype.
You cross the individual with a homozygous recessive individual.
Example: purple can be PP or Pp; a testcross will tell you which you have!

Figure 14.6, page 244, Campbell's Biology, 5th Edition