The X Factor

[wishbone]

I have a broodmare sired by Sea Hero. Her name is Too Victorious, 1996. Her dam carried one X chromosome with the X factor. From what I know about sex-linked inheritance, my mare should have a 50% chance of getting that chromosome. Pedigree analysis charts show her as not having the X factor. How is this determined?

[Pan Zareta]

Since a large heart gene(LH) has never been mapped, the trait is not actually proven to exist at all. Nonetheless there is compelling circumstantial evidence that there is a gene on the X that controls heart size. The db here generally follows the mares Marianna Haun identified as probable LH carriers, and when I pull up the pedigree for Too Victorious it shows that she may have rec'd. the trait from sire and/or dam. But the only way to know for sure what heart size is, is to have it 'scored' by EKG and ultrasound. If the mare has already been scored, that may be what the pedigree analysts are using to say that she doesn't have the trait. If she hasn't been scored, then I'd like to know on what basis they can rule it out. The only way I can think of would be if both sire & dam had been scored & found to have normal heart size, and even then there are so many mitigating factors during development which may effect the phenotype that a scoring of the mare herself would really be prefereable.

[wishbone]

Thanks for the info. To my knowledge, Too Victorious has never had her heart size evaluated. I believe the pedigree program simply omits the X-factor unless it can trace it with certainty.