Some Interesting Genetic Discoveries

[asal]

forget how often ive pointed out lines totaly clear of a problem can still turn one up due to mutations.

ok these articles refer to horfies but the implications are interesting to say the least

Genetic Mutation Caused Nonhereditary White Coat Color Pattern

by: Stacey Oke, DVM, MSc

December 26 2010, Article # 17433

Researchers recently discovered a new genetic mutation in a Thoroughbred foal that was born with large portions of nonpigmented skin. Whether another horse with the same rare mutation will be born is unknown, but the discovery has fueled researchers' pursuit of knowledge about coat color-related genetics and its potential relationship to serious health problems or death.

Essential to skin pigment is the function of a particular multipurpose gene, called KIT (an acronym for the actual genes involved), which the researchers examined in the current study. The KIT gene specifies the genetic code for a special protein called a tyrosine kinase receptor, expression of which is essential for the proper development of a variety of cell types, including red blood cells, mast cells of the immune system, and melanocytes (pigment-producing cells located in the bottom layer of the skin).

"KIT mutations cause abnormal melanocytes that do not produce pigment in the skin," explained Heather Holl, BSc, a PhD student in the Department of Animal Science at Cornell University. "The result is horses with pink skin and white hair. The amount of affected skin varies and ranges from small patches of depigmentation to white over the entire body."

To date, researchers have identified 14 different mutations involving the equine KIT gene, including the Sabino-1 and Tobiano color patterns.

Holl explained, "We suspected a new mutation after the birth of a Thoroughbred colt with extensive white markings. Both the parents had only small white markings and the sire had over 400 registered offspring without a single recorded dominant white foal."

Holl, together with Samantha A. Brooks, PhD, an assistant professor in the same department at Cornell, and Ernest Bailey, PhD, from the University of Kentucky's Gluck Equine Research Center, subsequently analyzed the DNA sequence of parts of the foal's KIT gene and found a novel deletion in the gene that involved just five base pairs of DNA out of the 2.7 million base pairs present in the equine genome.

"Neither parent had the mutation," Holl added.

The colt died unexpectedly at five weeks of age. It remains to be determined if the KIT mutation played a role in his death.

"Unfortunately, there is not much else we can do with this (case)," concluded Holl. "From the data we have, we cannot confirm the mutation was involved in the foal's death, and it is unlikely that another will be born like him; however, we (continue to) work with other white patterns in the horse, including other suspected dominant white cases."

Dominant white cases are uncommon. When a horse has one dominant white gene, the result will be a pure white horse that lacks pigment in the skin from birth, so they are easy to detect. However, a previous study of dominant white horses showed that breeding white horses to white horses can cause embryonic losses.

The study, "De novo mutation of KIT discovered as a result of a non-hereditary white coat colour pattern," was published in a special edition of Animal Genetics. The entire journal supplement, funded by the Dorothy Russell Havemeyer Foundation is available for free online.

this one can explain some mysteries why some females just never reproduce. if it can happen in the neddies i expect it can happen in canines and homo sapiens too. although obviously it cant be bred on...

XY Sex Reversal in Horses: The Genes Behind the Switch

by: Stacey Oke, DVM, MSc

December 27 2010, Article # 17448

Veterinary researchers have taken a leap forward in explaining XY sex reversal, the most common equine sex chromosome abnormality. A team of scientists from the University of Kentucky's Gluck Equine Research Center and the College of Veterinary Science at Texas A&M University have been examining the Y chromosome to determine what prompts a genetic mutation that causes seemingly healthy mares to be infertile.

XY sex reversal is the development of female genitalia in a horse possessing the male Y chromosome; i.e., the horse should have displayed male genitalia. When an abnormality affects sex differentiation, the developing equine fetus "defaults" to the female developmental pathway.

"The majority of affected horses have normal female genitalia and no stallionlike behaviors," said Teri L. Lear, PhD, an immunogenetics researcher in the molecular cytogenetics laboratory at the Gluck Center. "The sex reversal is often not noted unless there is a problem with infertility."

Some "XY mares," as they are called, however, show various degrees of masculinization, visible as abnormally developed reproductive tracts.

Little is known about the underlying cause of XY sex reversal. To shed light on this condition, Lear and her colleagues used state-of-the-art molecular techniques to map the Y chromosomes of XY mares.

"We looked at the Y chromosome from 18 XY mares (of various breeds) and found that there are actually two different forms of the condition," Lear explained. "The first form is a Y chromosome-linked form in which large sections of the DNA on the Y chromosome are missing. In the second form, the non-Y-linked form, the Y chromosome is the same as in normal males."

A closer look at the Y-linked form revealed that different regions of the DNA are missing, but in all mares with the Y-linked form, the gene called SRY, which is a sex-determining gene on the Y chromosome, was either partially or completely deleted.

"Horses which lack either some or all of the SRY gene will not develop into the 'right' sex, resulting in genetically male horses that look like mares," Lear continued.

Why horses possessing the entire SRY gene (the mares with non-Y linked sex reversal) become "sex reversed" is still unknown, however.

Lear said that this research provides a better understanding of a condition that translates to infertility in outwardly normal mares.

She added that despite the fact that these horses are genetically male, XY mares race against other mares, posing the question of whether they have an unfair advantage in competition.

"We do not know if the rest of the Y chromosome confers a physical advantage for racing or not," she added.

The study, "Molecular heterogeneity of XY sex reversal in horses," was published in a special edition of the journal Animal Genetics. The entire journal supplement, funded by the Dorothy Russell Havemeyer Foundation is available for free online.

Edited January 1, 2011 by asal

[Souff]

Which all goes to show that breeding is still an inexact science!

And there will probably be a few humans out there just wanting to use this as an excuse for their own inadequacies.

Happy New Year ASAL, may it be a goodie!

Souff

[asal]

LOL, never thought of it that way. was thinking of the so often times ive heard people being accused of being unethical when a bad gene is found in a pup they bred. nature hates sameness and continually strives for diversity. be it good results or disasters. but put a breeder into the equation and they cop the flack even when they didnt have anything to do with it as exemplified by the pair above. breeding just isnt black and white.

thanks for the good wishes.

we all need them.

n HAPPY NEW YEAR TO ALL.

[Leema]

Thanks for posting.