Clinical Genetics

Question 1

what is a gene loci?

Answer 1

defined position of a gene on the chromasone

Question 2

what are autosomal chromosomes?

Answer 2

any chromosomes that are not X or Y

Question 3

what are genes close together on the chromosome known as?

Answer 3

linked

Question 4

what are sex linked chromosomes?

Answer 4

those on the sex chromosomes

Question 5

what are alleles?

Answer 5

alternative forms of genes which have the same locus

Question 6

what are the types of alleles?

Answer 6

dominant
recessive
co-dominant

Question 7

what is epistasis?

Answer 7

non-allelic gene interaction

Question 8

what is incomplete penetrance of a gene?

Answer 8

gene is blocked by another

Question 9

what is variable expressivity?

Answer 9

genes being modified by other genes leading to a range of signs and symptoms in individuals

Question 10

what mutation is responsible for short tales in Manx cats?

Answer 10

dominant M mutation

normal cats are mm

Question 11

what is an example of a gene with variable penetrance?

Answer 11

M gene in manx cats - while it is dominant sometimes not the whole tail is missing

Question 12

what happens to Manx cats with MM?

Answer 12

die in utero as it is a lethal gene

Question 13

what is an example of epistatic gene interaction?

Answer 13

coat colour in labradors

Question 14

what does the 3 labrador coat colours result from?

Answer 14

differences in 2 gene loci that affect pigment expression

Question 15

how is labrador coat colour determined?

Answer 15

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

Question 16

what would an eebb larbrador look like?

Answer 16

yellow lab

brown nose, fur and lips

Question 17

how is tortoise shell coat produced in cats?

Answer 17

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.

Question 18

in what type of dog is the MDR1 dominant mutation seen?

Answer 18

herding dogs

Question 19

what is the result of the MDR1 gene mutation?

Answer 19

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

Question 20

what protein is affected by the MDR1 gene mutation?

Answer 20

P- glycoprotein

Question 21

what are 3 commonly used drugs who’s clearance is affected by the MDR1 gene?

Answer 21

ivermectin
milbemycin
selamectin

Question 22

what can be done if an MDR1 risk dog is in practice?

Answer 22

genetic testing

use of drugs that are not known to cause problems

Question 23

what genetic mutation is found in some greyhounds?

Answer 23

cytochrome P450 is altered so they have reduced ability to clear anaesthetic drugs from the brain and so recover slower

Question 24

is genetic testing available to see if there is cytochrome P450 mutation yet?

Answer 24

no

Question 25

what do dog blood types represent?

Answer 25

genetically determined markers on the surface of the animals RBC

Question 26

what is antigenicity?

Answer 26

Antigenicity - the likelihood that the immune system will react and make antibodies (alloantibodies) against a foreign substance.

Question 27

what is the blood grouping system formed of?

Answer 27

allelic blood types (two or more markers on same gene locus)

Question 28

what blood type do around 70% of dogs have?

Answer 28

DEA 1+

Question 29

when can DEA sensitisation occur?

Answer 29

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

Question 30

when is cross matching of donor and recipient blood needed in dogs?

Answer 30

transfusion history unknown previous transfusion previous transfusion reaction

Question 31

what blood type must be given to dogs if testing is not possible and blood type is unknown?

Answer 31

DEA 1 -

Question 32

what are the 3 blood types found in cats?

Answer 32

A B rare AB

Question 33

how does AB cta blood type interact with A and B?

Answer 33

AB recessive to A and co-dominant to B

Question 34

how dies cat type A blood interact with the other blood types?

Answer 34

A is dominant (to be type B cats must be homozygous BB)

Question 35

what is the most common blood type in cats?

Answer 35

A - 95%

Question 36

why must all cat blood donors and recipients be cross matched?

Answer 36

cats possess naturally occurring antibodies to other blood types that they don't have

Question 37

which blood type in cats produces higher titre of opposing antibodies?

Answer 37

type B has higher titre of anti-A antibodies

Question 38

what cat breeds are more likely to have blood type B?

Answer 38

``` Birmans, British shorthair, Devon rex Cornish rex, Ragdoll, Turkish Angora, Turkish Van ```

Question 39

what cat breeds are more likely to have blood type A?

Answer 39

``` DSH, Siamese, Main coon, American shorthair, Bengal, Norwegian Forest ```

Question 40

what is neonatal isoerythrolysis?

Answer 40

kittens receive anti-A antibodies to their own blood type (A) in mothers colostrum (as she is B and so has anti A) which leads to haemolytic anaemia and possibly death due to immunce destruction of their RBC

Question 41

what parent blood type combination can lead to neonatal isoerythrolysis in kittens?

Answer 41

Type B queen and type A/AB tom | type A is dominant

Question 42

what can be done to prevent neonatal erythrolysis in kittens?

Answer 42

blood type breeding pair to ensure that compatible blood types only mate (e.g. A and A, AB and A, A and B(Tom)) or B and B) take kittens off cat for first 24-26 hours (ethics)

Question 43

what are kennel club screening programmes used to do?

Answer 43

identify the likelihood of a heritable disease being passed on by parents and advise owners on the advisability of breeding

Question 44

what are the 2 main ways to test for heritable diseases?

Answer 44

genetic test - for directly inherited diseases | screening tests - for more complex, slower developing issues

Question 45

how is hip scoring performed?

Answer 45

VD radiograph of pelvis hips and femurs | strict guidelines for positioning and identification

Question 46

how is a hip score supplied?

Answer 46

2 experts analyse images and score them

Question 47

what is the total hip score out of?

Answer 47

53 for each hip | 106 in total

Question 48

what is a better hip score?

Answer 48

lower is better

Question 49

what is the issue with hip scoring?

Answer 49

dogs with poor hips will likely not have x-rays submitted for grading

Question 50

what is the elbow scheme designed to assess?

Answer 50

elbow dysplasia

Question 51

what radiographic view is needed for elbow scoring?

Answer 51

medio-lateral

Question 52

how is elbow dysplasia scored?

Answer 52

grade 1-3 | if elbow scores are different the higher of the 2 is used

Question 53

what is involved in the Kennel Club eye scheme?

Answer 53

panel of ophthalmologists assess for 12 hereditary eye conditions

Question 54

how often is the eye scheme assessment renewed?

Answer 54

dogs should be seen every year while breeding

Question 55

when is the first eye exam for the eye scheme performed?

Answer 55

6-12 weeks

Question 56

when do dogs no longer need to be assessed under the eye scheme?

Answer 56

post breeding ~8 years old

Question 57

what eye conditions are screened for under the eye scheme?

Answer 57

glaucoma, lens luxation etc | evolving list as more conditions/breeds added to watch list

Question 58

what is Chiari malformation?

Answer 58

fault in the development of the skull, causing part of the brain to protrude from the opening at the back of the skull

Question 59

what is Syringomyelia?

Answer 59

the presence of one or more fluid-filled pockets that may develop in the spinal cord, called syrinxes

Question 60

how can dogs be assessed for Chiari - like malformation and Syringomyelia?

Answer 60

MRI scans of at risk breeds

Question 61

what breeds are at risk of CM/SM?

Answer 61

cavalier king charles spaniels | griffon bruxellois

Question 62

at what age should screening for CM/SM start?

Answer 62

>1 year old

Question 63

what breeds are assessed by the respiratory function grading system?

Answer 63

french bulldogs pugs english bull dogs

Question 64

how is the respiratory function grading performed?

Answer 64

chest is auscultated by trained vet before and after 3 mins of quick paced exercise

Question 65

what are the respiratory function grades?

Answer 65

0 (clinically unaffected) -3 (severe)

Question 66

what is the aim of the heart screening scheme?

Answer 66

reduces chance of breeding puppies with MVD

Question 67

what dogs are involved in the heart screening scheme?

Answer 67

cavalier king charles spaniel

Question 68

what is assessed on heart screening?

Answer 68

murmur grade | mitral valve prolapse

Question 69

how are cavalier king charles spaniels scored on the heart scheme?

Answer 69

assigned a risk of getting mitral valve disease and risk of passing this condition on to offspring uses a traffic light system

Question 70

what are the grades used for murmur and mitral valve prolapse during heart scoring?

Answer 70

murmur grade 0, 1, 2 or 3+ | mitral valve prolapse - 0, 1, 2 or 3

Question 71

what does the location of the grades on the traffic light system of the heart scheme depend on?

Answer 71

age at testing

Question 72

what is cat genetic screening used for?

Answer 72

planning breeding programmes

Question 73

what can only be detected in cats through genetic testing?

Answer 73

late onset diseases or carrier status (recessive allele)

Question 74

how are cat genetic samples obtained?

Answer 74

mouth swabs - ensuring cheek cells are collected no just saliva

Question 75

what can be screened for during cat genetic testing?

Answer 75

diseases coat colour blood types

Question 76

when choosing what diseases to genetically screen cats for what must be considered?

Answer 76

breed predisposition - no need to screen if it is breed specific