The most-likely explanation for this inheritance pattern is that the secretor trait is

Question

A secretor (allele seS) is a person who secretes their blood type antigens into body fluids such as saliva. By comparison, a non-secretor (allele seNS) does not. A person's status as a secretor or non-secretor is independent of blood type. Consider the following inheritance pattern of this trait:







A.  incompletely dominant.

B.  recessive.

C.  dominant.

D.  co-dominant.



Clarify Question

· What is the key concept addressed by the question?

· What type of thinking is required?

· What key words does the question contain?



Gather Content

· What do you already know about allele dominance relationships?



Consider Possibilities

· So which dominance relationship best matches the data?



Choose Answer

· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?



Reflect on Process

· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?

Answer 1

C.  dominant.

Clarify Question
· What is the key concept addressed by the question?
        o This question focuses on allele dominance relationships.
· What type of thinking is required?
        o You must Evaluate the information, and decide the most likely explanation.
· What key words does the question contain?
        o Key terms are in the answer choices: recessive, dominant, incomplete dominant, and co-dominant. Polygenic means a trait is controlled by more than one gene. A dominant allele will predominate over a recessive allele in a heterozygote; we see the dominant phenotype. A recessive trait is only exhibited in the recessive homozygote. An incompletely dominant trait shows an intermediate phenotype in the heterozygote. A co-dominant trait is one where two different alleles are both exhibited in the heterozygote phenotype, such as blood type.

Gather Content
· What do you already know about allele dominance relationships?
        o You know that many genes have alleles with a dominant/recessive relationship. In a heterozygote, the dominant trait is seen. Some genes are co-dominant, and the heterozygote phenotype is an expression of both alleles. Other genes are incompletely dominant, with the heterozygote in-between two extremes.

Consider Possibilities
· So which dominance relationship best matches the data?
        o The most important result is the cross between secretor and non-secretor. This would produce a heterozygote. Since the heterozygote phenotype is “secretor”, what does this suggest?

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o Since the secretor phenotype is expressed in the heterozygote, the allele for that trait is dominant. This is also consistent with the results of the last cross – a monohybrid cross that produces a 3:1 phenotype ratio.

Reflect on Process
· Did your problem-solving process lead you to the correct answer? If not, where did the process break down or lead you astray? How can you revise your approach to produce a more desirable result?
        o This question required you to weigh and judge evidence – to Evaluate – and choose the best of the possible answers.
        o When reading a question, don’t let details like gene names distract you. To determine whether a trait is dominant, recessive, co-dominant, or incompletely dominant simply depends on whether the phenotype is exhibited in the heterozygote. If fully expressed, it is dominant. If not expressed, it is recessive. If expressed alongside another allele, it is co-dominant. If partially expressed, it is incompletely dominant.