Cat Genetic Disease
The Austrian empire in the mid-1800s was the important center of the arts, literature, and music. At the same time that Brahms produced his brilliant Variations on a Theme by Handel (1861), another genius, an Austrian monk named Gregor Men-del, was making one of the most important biological discoveries ever made: an organism’s traits, such as height, are regulated by two particles we now know as genes (Greek for “to give birth to”), one particle contributed by the female and the other by the male. Mendel performed his experiments on garden pea plants. He noticed that when he bred tall pea plants to short pea plants, all the offspring were tall. Mendel called this characteristic the dominant trait and the characteristic that”seemed to disappear,” to termed recessive.
When Mendel bred the offspring to each other, the result was three tall pea plants for every short pea plant a ratio of three to one. Mendel surmised that each offspring of the first breeding carried one dominant and one recessive particle and that in the breeding of the offspring, one short pea should be produced for every three tall pea plants.
Unfortunately, Vienna and the rest of the world neither understood nor cared about the biological sciences, which were considered antireligious. Gregor Men-del’s papers were burned after his death in 1884, and his great findings were not”rediscovered” until the beginning of the twentieth century.
What is this genetic material, which determines that like shall beget like? Genes are composed of deoxyribonucleic acid (DNA). This DNA is found in long strands called chromosomes in the nucleus of the billions of cells in your pet’s body. Every cell of your cat contains nineteen pairs of chromosomes.
Each gene controls the synthesis of one protein. Protein makes up about three-fourths of the body’s solids and is the building block of life. The majority of proteins are enzymes that regulate the chemical reactions in the cells. Blood, bone, hair, and muscle are primarily proteins. Hormones such as insulin are also proteins. A structural protein called connective tissue gives the skin its elasticity and the hair its form.
Throughout a lifetime there is a constant turnover of cells – daily wear and tear destroy skin, hair, and blood cells, but they are constantly being replaced, thanks to the cells’ ability to duplicate themselves. Before the cell divides, the chromosome forms a replica of itself (a process called replication). Each new cell has the exact number and order of genes as the original cell. Thousands upon thousands of activities occur and renew themselves daily in your pet’s body, thanks to a biological “blueprint,” called the genetic code, in the chromosomes.
Every part of your pet’s body (and even its temperament, to a large extent)is dependent on the chromosomes that were combined when its parents mated. The fertilized egg is a complete cell containing all the information that determines hereditary makeup. That cell divides in the mother cat’s uterus, and the developing embryo contains identical genetic makeup.
Let’s suppose you bred your pure tabby to a pure black cat. What color would you expect in the kittens? Tabby is dominant, and black is recessive. If a creature has two dominant genes for a trait, such as tabby. it is called a homozygote. Let’s use the letters TT for our homozygous female’s genes, and it for the male’s recessive black-coat genes. The kittens will all have one gene from each parent (Tt); this pairing of dominant and recessive genes is called heterozygote. Because tabby genes are dominant, all the kittens will be tabby. What if you bred one of these kittens to another heterozygote just like it?
Mendel’s Checkerboard Mother’s eggs
In the next generation, one of four kittens will have dominant tabby genes, two will be tabby heterozygotes like their parents. and one will have a pair of the parents’ recessive black-coat genes. In other words, two tabby parents can produce a black cat!
By now, you’re probably wondering what all this has to do with your cat’s health. It has a lot to do with it! As you already know, one gene carries the message for the production of one protein. But if the DNA gets mixed up. the gene carries an abnormality known as a mutation, a change from the normal pattern of inheritance that appears as a new or altered characteristic.
Inbreeding (mating closely related individuals, such as mother to son, father to daughter, or brother to sister) or linebreeding (mating more-distant relatives such as cousins) increases the chance of defects that require two recessive genes to come together or defects that require a polygenic union. Before breeding, the male and female should be checked by a veterinarian for defects or diseases that have a hereditary basis.
A disease called globoid cell leukodystrophy has been seen in a few kittens in which a genetic enzyme deficiency causes progressive degeneration of the nervous system and death in kittens between two and six months of age. It has a recessive pattern of inheritance: i.e., a kitten must receive two abnormal genes to produce the disease. A cat that has one normal gene and one abnormal gene is called a heterozygote carrier and will appear normal but can pass the abnormal gene to its offspring.
At the University of Pennsylvania, Veterinary School, Doctors Donald Patter-son and Peter Jezyk and their co-workers are studying the “fading puppy syn-drome: In human neonates and infants, genetic enzyme defects such as phenylketonuria (PKU) have been identified. Newborn infants can be screened for these hereditary metabolic defects and treated before mental retardation, liver or kidney dysfunction, or death occurs. Neonatal kittens that fail to thrive (they lose weight, have problems moving, and can’t maintain body temperature) may have similar disorders.
Metabolic screening is a new and important procedure in veterinary medicine. Dr. Jezyk points out, “In human medicine, 5 to 10 percent of all admissions to pediatric hospitals are for disorders which are genetic, while another 10 to 15 percent are for conditions with some genetic component.” The development of veterinary clinical specialties such as neurology, cardiology, dermatology, and ophthalmology has increased the accuracy of diagnosis and the recognition of genetic diseases. Improved methods of both prevention and treatment of parasitic, nutritional, and infectious diseases have decreased the importance of these illnesses and have brought to light diseases that are entirely or partially genetic in origin.
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