The curly toe phenotype is controlled by 4 genes that act in an additive manner. The environment does not have an effect on this trait. A dominant allele (represented by the capital letters) has 6 units of risk. A recessive allele (represented by the lower case letters) has 2 units of risk. Individuals with more than 35 units of risk have curly toes. Individuals with 35 or fewer risk units have straight toes. What is the highest number of risk units an individual can have with this model?
Give your answer as a whole number, not in words.
What is the phenotype of an individual of genotype AaBbCCDd? .
Curly Toes Straight Toes notype AAbbCcDd is married to an individual of genotype AaBbCCDd.
Is it possible for them to have a child with curly toes?

        Yes, the couple can have children with curly toes.

Explanation:

Available data:

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.

According to this information, and knowing how each allele contributes to the risk, we can say that the minimum units of risk are 16, determined by the recessive genotype aabbccdd. Each recessive allele contributes with 2 units of risk, so (aa=4units + bb=4 units + cc=4 units + dd=4 units) =  16 units.

Each time a dominant allele is present in the genotype, it adds 6 units to the total risk.    

What is the highest number of risk units an individual can have with this model?

48 units of risk, which corresponds to the genotype AABBCCDD. Each dominant allele contributes 6 units to the risk. There are 8 dominant alleles, so, 8x6=48 units.

What is the phenotype of an individual of genotype AaBbCCDd?

The individual has curly toes because it has a risk of 36 units, which is superior to the limit of 35 units. Dominant alleles A, B, C, C, D contribute with 30 units of risk (6x5), and recessive alleles a, b, d contribute 6 units of risk (3x2).

Cross:

Parentals) AAbbCcDd   x   AaBbCCDd

Gametes) AbCD, AbcD, AbCd, Abcd

               ABCD, ABCd, AbCD, AbCd, aBCD, aBCd, abCD, abCd

Punnett square)  AbCD                 AbcD               AbCd               Abcd

          ABCD    AABbCCDD     AABbCcDD     AABbCCDd     AABbCcDd

          ABCd    AABbCCDd      AABbCcDd     AABbCCdd      AABbCcdd

          AbCD    AAbbCCDD      AAbbCcDD    AAbbCCDd     AAbbCcDd

         AbCd     AAbbCCDd       AAbbCcDd     AAbbCCdd     AAbbCcdd

         aBCD     AaBbCCDD      AaBbCcDD      AaBbCCDd     AaBbCcDd

         aBCd     AaBbCCDd      AaBbCcDd      AaBbCCdd     AaBbCcdd

         abCD     AabbCCDD      AabbCcDD      AabbCCDd    AabbCcDd

         abCd      AabbCCDd      AabbCcDd      AabbCCdd        AabbCcdd

F1) 16 /32 = 1/2 individuals in the progeny are expected to have curly toes

     16 /32 = 1/2 individuals are expected to have straight toes

Is it possible for them to have a child with curly toes?

Yes, the couple can have children with curly toes.

To have curly toes, individuals must have more than 35 units of risk.

To have more than 35 units, individuals´ genotypes must carry at least 5 dominant alleles (which equal 30 units).

the answer is d. none of the above