Clinical Genetics Flashcards
what is a gene loci?
defined position of a gene on the chromasone
what are autosomal chromosomes?
any chromosomes that are not X or Y
what are genes close together on the chromosome known as?
linked
what are sex linked chromosomes?
those on the sex chromosomes
what are alleles?
alternative forms of genes which have the same locus
what are the types of alleles?
dominant
recessive
co-dominant
what is epistasis?
non-allelic gene interaction
what is incomplete penetrance of a gene?
gene is blocked by another
what is variable expressivity?
genes being modified by other genes leading to a range of signs and symptoms in individuals
what mutation is responsible for short tales in Manx cats?
dominant M mutation
normal cats are mm
what is an example of a gene with variable penetrance?
M gene in manx cats - while it is dominant sometimes not the whole tail is missing
what happens to Manx cats with MM?
die in utero as it is a lethal gene
what is an example of epistatic gene interaction?
coat colour in labradors
what does the 3 labrador coat colours result from?
differences in 2 gene loci that affect pigment expression
how is labrador coat colour determined?
presence of eumelanin in fur (and therefore dark coat) is dominant -E
yellow lab only possible with ee
concentration of pigment is determined by a different gene (B, b)
black (B) is dominant - bb required for brown
what would an eebb larbrador look like?
yellow lab
brown nose, fur and lips
how is tortoise shell coat produced in cats?
epistatic effects of the sex linked orange (O) gene on the autosomal black and tabby genes
Torty cats are heterozygous for the O gene. In every cell only one copy of the X gene is active, and it is random which copy is active. (will be O + or O-)
For cells where the O gene is active the hair coat will be orange, for cells where it is inactive the hair coat will be black or tabby, depending on the cats autosomal genetic makeup for the black tabby genes.
in what type of dog is the MDR1 dominant mutation seen?
herding dogs
what is the result of the MDR1 gene mutation?
these dogs are more susceptible to drug toxicosis due to an alteration in the protein responsible for clearing drugs over the blood brain barrier and excreting them
what protein is affected by the MDR1 gene mutation?
P- glycoprotein
what are 3 commonly used drugs who’s clearance is affected by the MDR1 gene?
ivermectin
milbemycin
selamectin
what can be done if an MDR1 risk dog is in practice?
genetic testing
use of drugs that are not known to cause problems
what genetic mutation is found in some greyhounds?
cytochrome P450 is altered so they have reduced ability to clear anaesthetic drugs from the brain and so recover slower
is genetic testing available to see if there is cytochrome P450 mutation yet?
no
what do dog blood types represent?
genetically determined markers on the surface of the animals RBC
what is antigenicity?
Antigenicity - the likelihood that the immune system will react and make antibodies (alloantibodies) against a foreign substance.
what is the blood grouping system formed of?
allelic blood types (two or more markers on same gene locus)
what blood type do around 70% of dogs have?
DEA 1+
when can DEA sensitisation occur?
if DEA 1 - dog is exposed to DEA 1 + blood they will form alloantibodies to the antigens on the DEA + blood
this can lead to delayed transfusion reaction (haemolysis) or severe transfusion reaction if another DEA 1+ transfusion is performed
when is cross matching of donor and recipient blood needed in dogs?
transfusion history unknown
previous transfusion
previous transfusion reaction