Answer:
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.
- white flower → aabb → all recessive alleles
- light pink → Aabb or aaBb → One dominant allele
- pink flower → AAbb or aaBB or AaBb → Two dominant alleles
- red flower → AaBB or AABb → Three dominant alleles
- dark red → AABB → All dominant alleles
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
- 1/16 AABB → dark red >> 4 dominant alleles
- 2/16 AABb → red >> 3 dominant alleles
- 1/16 AAbb → pink >> 2 dominant alleles
- 2/16 AaBB → red >> 3 dominant alleles
- 4/16 AaBb → pink >> 2 dominant alleles
- 2/16 Aabb → light pink >> 1 dominant allele
- 1/16 aaBB → pink >> 2 dominant alleles
- 2/16 aaBb → light pink >> 1 dominan allele
- 1/16 aabb → white >> 0 dominant allele
Phenotype
- 1/16 dark red
- 4/16 red
- 6/16 pink
- 4/16 light pink
- 1/16 white
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
