Re: female mice have litters half as large as normal when carrying gene G6PD

Dear Joanne,

I'm not familiar with the details of the experimental system you describe, but I'll try to interpret the genetics as best as I can for you.

I'll first review some of the basics of this mutation.  G6PD deficiency is an X chromosome-linked, recessive gene.  This means that all "normal" mice, as well as humans, must carry either 1 or 2 non-defective ("wild- type") G6PD (glucose-6-phosphate dehydrogenase) genes.  This state can also be referred to as "phenotypically G6PD+".  Since it is X-linked, males carry only one copy, or "allele", of G6PD.  If that copy is defective, a male becomes "phenotypically G6PD-".  Since females carry 2 alleles, 1 on each X chromosome, only 1 needs to be wild-type in order for a female to be phenotypically G6PD+, since mutants are recessive.  The following web site from the Univ. of Iowa is a great "Introduction to G6PD Deficiency".

Although I can't be certain from your question, it sounds like the female mice you describe are actually G6PD "deficient", indicating that they would have to be carrying 2 defective alleles (homozygous) of the G6PD gene.  If that is the case, then none of the fetuses resulting from mating with a G6PD- male could produce G6PD, since neither the mother nor the father could pass on any wild-type alleles.  If the mother carries only 1 defective allele (heterozygous), then the odds of the offspring being G6PD- would be 1:2 when mated with a G6PD- male.  But, as far as I can tell, the ability to produce G6PD has little effect on fetal survival, otherwise the deficiency would not be as common as it is in the population.  Thus, G6PD+ or G6PD- fetuses should develope just fine in a heterozygous mother.  Although not genetically possible with a G6PD- father, G6PD+ females resulting from mating with a G6PD+ father should also develope normally in a homozygous G6PD- mother.  Consequently, the genetic background of the potential offspring, or of the father for that matter, would have little effect on litter size, which generally depends mainly upon the physiological status of the mother, to the best of my knowledge.

I hope that I have understood & managed to address your questions adequately.  But if I have not, PLEASE feel free to request further clarification.

Thanks a lot,

Jeff