For genetic questions, what is the definition of a carrier?

[davcro]

---

Members do not see this ad.

From TPR:

Color blindness is a recessive trait passed on through a sex-linked gene on the X chromosome. If a woman who carries the trait for color blindness has a child with a man who is color blind, what is the probability that a female offspring will be a carrier?

A 0%
B 25%
C 50%
D 100%

Answer: http://www.clker.com/clipart-27984.html

Rationale from the answer key: 50% of female children will be homozygous colorblind and 50% will be heterozygous carriers.

I thought the homozygous were still carriers because the have the gene. So I answered 100%. Do you have to be recessive to be called a carrier?

 

[folktale]

A carrier just means the mom carries one recessive gene for color blindness, but is not expressing the trait because there's a wild type that's normal. Thus, she is heterozygous. Having both recessive genes will result in expression of color blindness, making the idea of being a carrier obsolete.

 

[MedPR]

From TPR:

Color blindness is a recessive trait passed on through a sex-linked gene on the X chromosome. If a woman who carries the trait for color blindness has a child with a man who is color blind, what is the probability that a female offspring will be a carrier?

A 0%
B 25%
C 50%
D 100%

Answer: http://www.clker.com/clipart-27984.html

Rationale from the answer key: 50% of female children will be homozygous colorblind and 50% will be heterozygous carriers.

I thought the homozygous were still carriers because the have the gene. So I answered 100%. Do you have to be recessive to be called a carrier?

I picked 100% too.

 

[MrNeuro]

A carrier just means the mom carries one recessive gene for color blindness, but is not expressing the trait because there's a wild type that's normal. Thus, she is heterozygous. Having both recessive genes will result in expression of color blindness, making the idea of being a carrier obsolete.

👍

 

[MedPR]

A carrier just means the mom carries one recessive gene for color blindness, but is not expressing the trait because there's a wild type that's normal. Thus, she is heterozygous. Having both recessive genes will result in expression of color blindness, making the idea of being a carrier obsolete.

So men cannot be carriers for color blindness?

 

[folktale]

So men cannot be carriers for color blindness?

No, because the trait is sex-linked to the X chromosome, not the Y. And Men have an XY instead of an XX, therefore, they are not capable of being carriers. It's either they are color-blind, or not.

 

[MedPR]

That's a good distinction to know. I always thought affected individuals were still considered carriers. I'm glad this didn't show up on my MCAT!

 

[davcro]

A carrier just means the mom carries one recessive gene for color blindness, but is not expressing the trait because there's a wild type that's normal. Thus, she is heterozygous. Having both recessive genes will result in expression of color blindness, making the idea of being a carrier obsolete.

Wikipedia agrees:

"A genetic carrier (or just carrier), is a person or other organism that has inherited a genetic trait or mutation, but who does not display that trait or show symptoms of the disease. They are, however, able to pass the gene onto their offspring, who may then express the gene. This phenomenon is a direct result of the recessive nature of many genes."

Thanks for the clarification.

 

[folktale]

Wikipedia agrees:

"A genetic carrier (or just carrier), is a person or other organism that has inherited a genetic trait or mutation, but who does not display that trait or show symptoms of the disease. They are, however, able to pass the gene onto their offspring, who may then express the gene. This phenomenon is a direct result of the recessive nature of many genes."

Thanks for the clarification.

You're welcome.

 

[JLeBling]

I think the real question here is, why are so many colour blind people getting "married" to each other?