vet-tech-therio-ch-3

• genetic (heritable) or due to external factors (non-genetic in origin)
• eg tail-less cat
• 1. due to trauma - can't pass characteristic to offspring
• 2. Manx cat - genetically inherited - can pass characteristic to offspring

an external or environmental factor produces a phenotype identical to that produced by a gene

• incidence of that characteristic will be higher in related individuals
• related individuals more likely to have similar genes

• autosomal dominant
• autosomal recessive
• sex-linked dominant
• sex-linked recessive

• can help to determine if characteristic is genetic
• need enough of a pedigree (big enough statistical sample) to be able to determine

• characteristic caused by the dominant gene will be expressed in every individual carrying the gene
• 1. defect carried from generation to generation w/o skipping a generation
• 2. every affected offspring must have one affected parent (except mutations)
• 3. normal offspring from affected parents cannot pass on the condition
• 4. condition will affect an equal # of males and females
• 5. normal individual crossed with heterozygous affected individual can produce an affected individual
• affected = AA or Aa
• normal = aa

• recessive genes will only be expressed in individuals with 2 copies (homozygous for that gene)
• if individual has only 1 copy, gene can be passed from generation to generation w/o being revealed until an individual receives 2 copies of the gene and the condition is expressed
• 1. the diorder may skip a generation
• 2. all offspring of 2 affected parents will be affected (offspring homozygous)
• 3. equal # of males and females affected
• 4. in rare disorder
• 4a. most affected individuals will have normal parents (heterozygous carriers)
• 4b. most normal parents producing affected offspring will be more closely related than other animals in population as they must carry recessive (rare in rare disorder)
• 4c. if both parents heterozygous carriers - 1 in 4 offspring affected
• 4d. matings between an affected and unrelated normal animal will produce only normal offspring (carrier)
• affected = aa
• normal = AA
• carriers = Aa

• located on the X chromosome
• 1. all animals carrying the gene will express it, normal individuals will not carry it
• 2. every affected offspring must have at least one affected parent
• 3. affected males mated to normal females will not pass the gene to any of their sons
• 4. affected males mated to normal females will pass the gene to all their dauhters
• 5. rare condition - incidence of defect or disease in females is 2x that in males
• affected = X(A)X(A), X(A)X(a), X(A)Y
• normal = X(a)X(a), X(a)Y

• located on the X chromosome
• in male, recessive X can be expressed because there is no 2nd dominant gene copy to maske the

• 1. defect may skip a generation
• 2. all offspring of 2 affected parents will be affected
• 3. incidence is lower in females than males
• 4. rare condition
• 4a. most affected individuals will be males
• 4b. will result from normal parents (female will be carrier)
• affected = X(a)X(a), X(a)Y
• normal = X(A)X(A), X(A)Y
• carriers = X(A)X(a)

• can indicate whether carrying a dominant gene
• can indicate whether homozygous for a recessive gene
• difficult to determine from a pedigree and it phenotype if an animal is carrier of recessive gene