ANSWER KEY A geneticist studying the inheritance of color in flowers crossed a pure white flower (aabb) with a dark red flower (AABB) and got all pink offspring. Interbreeding the pink flowers produced the following data: 43 dark red 162 red 245 pink 166 light pink 41 white a) Why is this particular example a case of polygenic inheritance

Because there are two genes interacting to define the flower color, and each dominant allele of these genes contributes to defining the color.

Explanation:

The term quantitative heritability refers to the transmission of a phenotypic trait in which expression depends on the additive effect of a series of genes.  

Polygenic heritability occurs when a trait results from the interaction of more than one gene. And these genes can also have more than two alleles. The action of many genes and alleles can cause many different combinations that are the reason for genotypic graduation.  

Quantitative traits are those that can be measure, such as longitude, weight, eggs laid per female, among others. These characters do not group individuals by any precise and clear categories. Instead, they group individuals in many different categories that depend on how the genes were intercrossed and distributed during meiosis. The result depends on the magnitude in which each allele contributes to the final phenotype and genotype. When they interact, they create a gradation in phenotypes, according to the level of contribution.  

In the exposed example, we have two diallelic genes involved in the color of the flowers. Each dominant allele equally contributes to defining the pigment and the spectrum of phenotypes of each flower color.

1st Cross:

Parentals) AABB    x     aabb

F1) 100% AaBb  Pink flowers

2nd Cross:

Parentals) AaBb    x    AaBb

Gametes) AB, Ab, aB, ab

                AB, Ab, aB, ab

Punnett square)     AB          Ab         aB          ab

                  AB     AABB     AABb    AaBB     AaBb

                  Ab     AABb     AAbb     AaBb     AAbb

                  aB     AaBB      AaBb     aaBB     aaBb

                  ab     AaBb      Aabb      aaBb     aabb

F2) Genotype

   Phenotype

 Total number of individuals in the F2 = 657

657 individuals 16

43 dark X = 1

162 red X = 4

245 pink X = 6

166 light pink X = 4

41 white X = 1

the overall balanced equation

6co2 + 6h2o > c6h12o6 + 6o2

sunlight energy

where: co2 = carbon dioxide

h2o = water

light energy is required

c6h12o6 = glucose

o2 = oxygen

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