The genotypic ratio produced in the last cross is most likely

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.  3:1

B.  1:2:1

C.  2:1

D.  9:3:3:1

E.  1:1



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 this type of cross?



Consider Possibilities

· What other information is related to the question? Which information is most useful?



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

B.  1:2:1

Clarify Question
· What is the key concept addressed by the question?
        o This is basically a monohybrid cross like that seen in the text for Mendel’s purple pea flowers.
· What type of thinking is required?
        o You need to Apply what you know about monohybrid crosses and the use of Punnett squares.
· What key words does the question contain?
        o The genotypic ratio is the ratio of genotypes: that is, distinct allele combinations. Genotypes may be different even if they produce the same phenotype.

Gather Content
· What do you already know about this type of cross?
        o This last cross is of two people heterozygous for one gene – a monohybrid cross. This is similar to the cross of purple-flowered pea plants in the text.

Consider Possibilities
· What other information is related to the question? Which information is most useful?
        o Punnett squares are a useful way to determine both genotype and phenotype ratios.

Choose Answer
· Given what you now know, what information and/or problem solving approach is most likely to produce the correct answer?
        o You could do this in your head, but drawing a Punnett square on scrap paper is an easier approach. Write the possible parental gametes along both the top and side: seS and seNS. Fill in the 4 combinations. Note that two are the same, seS/seNS – thus we get a 1:2:1 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 Apply your knowledge and understanding to this unfamiliar situation.
        o If you chose the answer “3:1”, think about the difference between and genotypic ratio and a phenotypic ratio.