In most situations, this occurs when both parent animals are asymptomatic carriers of the disorder.īecause the disorder is recessive, an animal who carries one copy of the abnormal gene and one copy of the normal gene will not show signs of disease. With an autosomal recessive genetic disorder, an animal must receive two copies of the abnormal gene (one from each parent) in order to show signs of the disorder. How does an autosomal dominant disorder differ from an autosomal recessive disorder? By not breeding affected cats, breeders have significantly reduced the prevalence of PKD in Persian cats.
More recently, DNA tests have been developed that can detect affected cats with a simple cheek swab. Initially, cats who were intended for breeding were evaluated by ultrasound cats who had normal kidneys were suitable for breeding, while cats with abnormal kidneys were not bred. After recognizing that this is an autosomal dominant disorder, meaning that there are no healthy carriers of this condition and any affected cat must have at least one affected parent, careful breeding efforts have now significantly reduced the prevalence of this disease. Historically, as many as 50% of Persian cats were affected with this condition. In this condition, hereditary kidney abnormalities can lead to premature kidney failure and death. Polycystic kidney disease (PKD) in Persian cats is an example of an autosomal dominant trait. "For an autosomal dominant disorder, only one copy of a given allele is necessary to produce the trait." All affected animals can be readily detected and removed from breeding programs. Autosomal dominant genetic disorders are uncommon in breeding, because there are no asymptomatic carriers. Affected animals may express the trait to varying degrees, but all animals who carry a copy of the gene will be affected by the trait. If an animal receives an abnormal allele from one parent and a normal allele from the other parent, the abnormal trait will be expressed. What is autosomal dominant inheritance?įor an autosomal dominant disorder, only one copy of a given allele is necessary to produce the trait. (Receiving a Y chromosome from their father makes them XY, leading them to be male.) Because males only receive one copy of the X chromosome, they are more likely to demonstrate sex-linked characteristics than females. While females receive two copies of the X chromosome (XX), males only receive one copy of the X chromosome. Some disorders are sex-linked, meaning that they are found on the X chromosome. This is called autosomal recessive inheritance. Other alleles are recessive, meaning that both alleles must be the same in order for the disorder to be observed. This is referred to as an autosomal dominant trait.
Some alleles are dominant, meaning that only a single copy of that allele is necessary to express the trait. The result of each combination of alleles is determined by a trait’s mode of inheritance. With two potentially-different alleles present for each gene, how does the body know which allele to express? Each animal receives one copy of each allele from his mother and one copy from his father. For example, in the eye color gene, there may be a blue allele, green allele, brown allele, or other color. Each copy of the gene is referred to as an allele. This will result in the offspring’s cells again having paired sets of chromosomes, with two copies of each gene. When an egg is fertilized by the sperm, the new offspring will receive one chromosome from each parent. "When an egg is fertilized by the sperm, the new offspring will receive one chromosome from each parent." Therefore, each reproductive cells contains only one copy of each gene. During the formation of these reproductive cells, each cell gets only one copy of each chromosome. The exception to this rule is sperm cells and egg cells. While a human has 46 chromosomes (23 pairs), a cat has 38 chromosomes (19 pairs) and a dog has 78 chromosomes (39 pairs). Each cell contains two separate copies of each gene (alleles). Chromosomes are found in pairs within the cell. Each chromosome contains hundreds or thousands of different genes. Inside each cell, the DNA is bound into a unit called a chromosome. For example, there are genes that determine eye color, coat color, and other body characteristics. A gene is a specific DNA sequence that leads to the expression of an inherited characteristic.
This genetic code is found in the animal’s DNA, a long molecule that is present in every cell in the body (see handout "Genetic Basics: Understanding DNA"). Inherited traits or disorders are passed down in an animal’s genetic code. What determines an animal’s genetic makeup?