Question

In order for an inherited genetic mutation to result in a phenotypic change for a recessive trait, which of the following must occur?

A:The mutation must be inherited on the x chromosome.
B:The mutation must be inherited by both parents.
C:The mutation must be inherited from the mother.
D:The mutation must be inherited from the father.

I don't know the answer to the question. Can you help me out, even explain why that answer is correct so I understand it completely?

Answer 1

How is this my first question? My engagement even says I am at 52.

Answer 2

I'm shaky on this, so take with a grain of salt:

If you're seeing a trait, and it's recessive, it's rr, for example, meaning that both parents had to at least be heterozygous or recessively homozygous.

Therefore, I *think* it's B. However, I'm not confident (I passed genetics, but it's been a while!).

I'm hoping that that helps... I'm getting caught up in the mutation portion of the question, but suspect/hope that may be a distractor.
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Answer 3

@clstal is quite right. With the info you are given, it is most likely B and the reasons discussed are correct.

Mutations come in two flavours: gain of function mutations, which confer some increased or different function on the protein product, or loss of function mutations which reduce the functionality of the protein product.

Here the question becomes a little sticky:

If the mutation is a gain of function mutation, then likely just having one copy of the new allele will confer the mutant phenotype on the organism. Unless the mutation is on the X chromosome, it won't matter which parent it came from. If the mutation is a loss of function mutation, then usually the non-mutant allele will produce enough protein product to cover for its loss.

That is, gain of function mutations tend to confer a dominant phenotype; loss of function mutations tend to confer a recessive phenotype.

The problem doesn't ask for that but I mention it because it might save you some angst and confusion about the biologic basis of dominance/recessiveness in mutations...

Answer 4

@blues, nice one :) from a simple perspective of sex based genetics;
Well if its a male patient the mutation must be on the mothers X chromosome and the Y from the father, he wont get any genetic info from the fathers Y and therefore doesnt need both parents, just dear ol'mum for the gene to be expressed.
If female she needs both X's to have the recessive trait therefore both parents must pass this on. the mother can be a carrier but the father will express the gene so B, C and dependant of sex, D can be correct from my interpretation of it

Answer 5

Thank you all! Sorry, I haven't been here to respond. I understand the question perfectly now!

Answer 6

Thats the aim of the game XD