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Albinism
 

Prevalence

 

Albinism among Chins is so rare as to be virtually non-existent.

 

Albinos versus Pink White

 

Unfortunately, many think Pink Whites are Albinos. They are not, even though, physically, both would look very similar. Anyone selling an "Albino" or "Albino White" is most likely [ie., 99.9% of the time] selling a Pink White instead.

Pink White is simply a Tower Beige-Wilson White cross and is characterized by a totally white body along with pink ears and reddish/pink eyes. The pink ears and reddish eyes are contributed by the Beige trait. If mated to a Standard Grey, a Pink White [that is heterozygous for Beige, the most common condition] will produce litters that will consist of, on average, 25% Pink White, 25% Wilson White, 25% hetero Tower Beige, and 25% Standard Grey.

From just physical appearance ["phenotype"] alone, it would be difficult to distinguish an Albino from a Pink White. Nevertheless, one would be able to differentiate the two from their offspring [and parentage, if known] and their relative health [more on this later].

 

Albinism is Recessive

 

First of all, what is "albinism"? Basically, it is the absence, either totally or partially, of colour pigmentation in skin, fur, iris and retinal cells. Albinism is typically a recessive trait that is carried invisibly in the heterozygous state but is expressed in the homozygous state. So, an Albino individual would have to receive copies of the trait from both parents.

Albinism differs from Pink White in which the constituent colour traits, Wilson White [a.k.a. DEW - "Dark Eyed Whites" in other species] and Tower Beige traits are dominant traits.

 

Type 1 Albinism: OCA1

 

The classic type of albinism, termed "OculoCutaneous Albinism, type 1" [OCA1] ("oculo" refers to eyes and "cutaneous" refers to skin) , involves a mutation in the gene responsible for the production of the enzyme tyrosinase which in turn is responsible for pigmentation/colour production in skin, fur, iris, and retinal cells. So, these OCA1 albinos would be "tyrosinase negative" and have no colour pigmentation whatsoever. There are apparently cases in which the mutation of the tyrosinase gene results in the production of tyrosinase with some residual effects, resulting in individuals that are "yellow", "brown", or "red" albinos: these are called "tyrosinase positive" or "partial" albinos. The mutation of the tyrosinase gene involved in the OCA1 type of albinism is generally referred to as "C series" mutations by geneticists and is typically recessive.

According to "Lani Ritchey" lritchey@sric.sri.com , you can test for tyrosinase-negativity by soaking a sample of hair bulbs [from a fur follicle] in L-DOPA which is the chemical precusor to melanin. If the hair bulb darkens, then the animal is normally pigmented and other genes are controlling the color [see next paragraph] . If no colour changes occur, then the individual would be tyrosinase negative or OCA1. [This of course assumes that the underlying colour trait is not already Wilson White.]

Most humans affected with OCA1 albinism have white hair, milky white skin, and blue eyes at birth. The irises can be very light blue and translucent such that the whole iris appears pink or red in ambient or bright light. During the first and second decade of life, the irises usually become a darker blue and may remain translucent or become lightly pigmented with reduced translucency.

 

Type 2 Albinism: OCA2

 

The second type of albinism, OCA2, does not involve any mutation of the tyrosinase gene [that is, tyrosinase production is normal] but rather some malfunction in the production and distribution of melanosomes. Melanosomes are small granules of melanin [pigment] in special skin, fur, iris, and retinal cells called "melanocytes". This type of albinism is called the "P series" mutation by geneticists and often referred to as "pink-eyed dilution" mutations in species such as mice by breeders. It too is generally a recessive trait.

 

Albinism masks underlying colours

 

Regardless of which type of albinism an Albino individual possesses, the albinism trait operates in an "epistatic" fashion, which means that in the homozygous state, it covers or "masks" the effect of any normal underlying colour trait. So, it is possible for albinism to occur with any Chin colour as long as both parents are at least heterozygous [a.k.a. "carriers"] of the same albinism trait. Furthermore, if mated to another without the albinism trait, an Albino would produce normal-coloured offspring [all would be carriers of the albino trait, however]. For instance, if mated to a Standard Grey, an albino will produce 100% normal-coloured offspring [that is, Standard Grey] , but all of them will be carriers of the albino trait.

 

Punnett Square for Albinism

 

A suitable alleleic code for albinism would be a for the expressed state and A for the non-expressed [ie., normal] state. As illustrated in the second Punnett Square below, one can use g instead of A to represent the non-expressed state. Thus, an Albino would be represented by a-a . An Albino Carrier would correspondingly be represented by either a-A or a-g . Finally, a Standard Grey could be represented in this context by either A-A or g-g

The mating of an Albino [ a-a ] with a Standard Grey [ A-A or g-g ] is illustrated by the following Punnett Squares:

  Albino
Standard Grey   X   a a
A a-A a-A
A a-A a-A
                    
  Albino
Standard Grey   X   a a
g a-g g-g
g a-g g-g

All of the offspring would be Albino Carriers [ a-A or a-g ] but would look like normal Standard Greys.

 

Health Problems

 

In general, there are a host of health problems associated with albinism. The albinism trait affects melanocytes which are concentrated in the skin, in hair follicles, and in the iris and retina of the eye. The group of cells in the fetus which eventually become melanocytes, the neural crest cells, are also involved in the development of some nervous tissues. These include essential elements of the auditory and visual systems of the brain. And even seemingly unrelated tissues, such as blood vessel walls, can be affected by lack of pigment. Additionally, the C and P genes are closely linked to other genes, which in some cases are responsible for other essential processes such as liver, kidney, or blood clotting function. Therefore, as outlined below, the albinism syndrome may be accompanied by a wide variety of disorders besides just the obvious loss of fur color.

Visual problems experienced by albinos [human or non-human] may include nystagmus [rapid back-and-forth movement of the eyes] , strabismus [crossed eyes, wandering eye, "lazy" eye, "wall" eye] , photosensitivity/photophobia, either hyperopia [far-sightedness] or myopia [near-sightedness] , and/or astigmatism [blurred vision] , as well as a loss of depth perception caused by the abnormalities in the optic nerves. These problems can been seen in both "complete" and "partial" albinos. A common behaviour associated with these visual problems is the sweeping of the head back and forth sideways in order to generate a proper visual image.

Albinism may be accompanied by a wide range of general health problems. Some types of albinism affect the immune system, liver, or clotting ability, and others may cause other physiological abnormalities such as defects of the kidneys or thymus, anemia, inner ear defects, megacolon, neurological abnormalities, skeletal defects, microphthalmia, osteopetrosis, spina bifida, and sterility, just to name a few. Albinism in general predisposes animals to skin cancer as well as photosensitivity/photophobia. In some species, some types of albinism are even lethal!

Longevity: An albino typically has only 1/2 to 2/3 of normal life expectancy.

 

Sources of information

 

An extremely useful web site about albinism is http://whitedobes.doberinfo.com/ , a web site about White Doberman dogs written by Ione L. Smith, DVM facts@whitedobes.com .

One should also consult his references NOAH, The National Organization for Albinism and Hypopigmentation , and International Albinism Center at the Univeristy of Minnesota

Although I cannot vouch for its accuracy, another interesting site is http://albinism.med.umn.edu/facts.htm



 
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