Monday, November 8, 2010

Life Lines 30


Nedra and I visited her cousin, Michael Walsh, in Manhattan, who came in from Indiana to exhibit his dog at the Westminster dog show at Madison Square Garden. He is a veterinarian with a large practice in Crown Point and he breeds and judges Vizslas, hunter dogs of Hungarian origin that are one of the recognized breeds of the American Kennel Club. I asked him a lot of questions about dog genetics because dogs are widely used in studying human inherited diseases (about 85 percent of human genetic disorders have a counterpart in dogs). Vizslas are very attractive dogs with a soft brown color (golden rust, as the fanciers like to call it), floppy ears, long legs, and an up-curved tail that is usually cropped at the more spindly upper third. They tend to be less allergenic to owners who have allergies. Walsh said that was because they lacked an undercoat of hair. This makes them more suitable for indoor living during winter because fur is an adaptation of hair to temperature regulation. Hair is composed of a protein called keratin. It is manufactured in a follicle and combined with dead cells to make hair and the shedding of dead cells from the hair causes dander, which is what makes allergic people sensitive to the presence of animal fur.

We humans are mammals and have hair. We have a primary hair and no undercoat because we use clothing to regulate body temperature instead of fur. Why we lost that capacity to be furry like other mammals is still an evolutionary problem with lots of theories and no good evidence to sort them out into likely or erroneous views. The need for our skin to produce enough vitamin D for bone growth is one such theory. We are one of the few mammals that have difficulty synthesizing our own vitamin D. Each of our human head hairs grows continuously and after about 2 to 6 years it falls out and is replaced at the same follicle with a new hair. This continues for most non-bald people until they hit old age when the rate of falling out exceeds the capacity to produce new hairs and hair begins to thin out and baldness increases in extent. Aging involves a reduction in replacement of all cells in the body, which is why we shrink and wrinkle. Why humans have continuous hair growth of head hair is still unresolved. The gene for regulating head hair in apes is produced by a gene, which is silenced (it is called a pseudogene) in humans. Apes don’t need haircuts. Their head hair stops growing like their body hair and like our own body hair. I learned that pattern baldness could occur in some breeds of dogs. So can stripes appear in some breeds (even humans have occasional persons with a stripe of white hair in an otherwise head of hair with full color). If a human head hair is transplanted to a leg, it continues to grow like head hair but eventually stops. If a leg hair is transplanted to a human scalp, it fails to grow like a head hair.

There are several breeds of hairless dogs that would be safe for the allergic daughter of the Obama family but they require a lot of care. Almost as good are breeds of dogs that lack undercoats and thus produce less shedding seasonally and thus less dander to float around the White House. Complicating the presidential choice is a desire for a hybrid of some sort and hence the attention to Labradoodles, which are hybrids, but lack an undercoat of hair, making them front runners in this search.

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