Calico cats are female. The patches of fur color result from X inactivation, silencing fur color genes on one X chromosome or the other. However, extremely rarely, there can be a male calico. Describe the genetics necessary for a male calico cat.

Question

A.  XX with a translocation of the SRY gene onto one of the X chromosomes.
B.  XY with a mutation in the SRY gene.
C.  XX with a translocation of the testosterone gene onto one of the X chromosomes.
D.  XY with a mutation in the estrogen gene.


Clarify Question
What is the key concept addressed by the question?

What type of thinking is required?


Gather Content
What do you already know about calico cats? What other information is related to the question?

Choose Answer
Given what you now know, what information 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

A.  XX with a translocation of the SRY gene onto one of the X chromosomes.


Clarify Question
What is the key concept addressed by the question?
     · The concept addressed in this question is the mechanism needed to produce a male that is heterozygous for X-linked traits.

What type of thinking is required?
     · Evaluate level:
       o This question is asking you to weigh and judge, or evaluate, the genotype of a male calico cat.


Gather Content
What do you already know about calico cats? What other information is related to the question?
      · In cats, an XX genotype codes for a female, while an XY genotype is male.
     · Although we often say that the Y determines male sex, in fact it is the single SRY gene on the Y chromosome that matters.
     · Females inactivate one of their X chromosomes, but the source of the inactivated X is random, and varies in different tissues.
     · Within a female, the inactivation of the paternal X is some spots and inactivation of the maternal X in other spots causes a characteristic patchy phenotype.
     · Occasionally, translocations occur in which a portion of one chromosome is attached to another. This can have significant impacts on phenotype.


Choose Answer
Given what you now know, what information is most likely to produce the correct answer?
     · A genotype of XY with a mutation in either the SRY or estrogen gene would still result in the expression of only one X chromosome, which would not provide the calico phenotype.
     · A translocation of the testosterone gene onto an X chromosome would not result in a male individual. Females have and express the gene for testosterone anyway, just at lower levels than males.
     · If a small region including SRY+ translocated and attached to the X chromosome, the resulting cat would inactivate one X chromosome and produce calico patches since it would have two X chromosomes, but would produce testosterone and have male sexual characteristics.


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?
     · Evaluate level:
       o Answering this question correctly depended on your ability to weigh and judge, or evaluate, the calico phenotype. If you got an incorrect answer, did you remember that to produce the calico phenotype, two X chromosomes must be present, or the criteria to determine the male sex in cats comes from the SRY gene? Did you have trouble weighing the merits of the calico phenotype relative to gender to determine the correct answer?