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Flashcards in Clinical Genetics Deck (76)
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1
Q

what is a gene loci?

A

defined position of a gene on the chromasone

2
Q

what are autosomal chromosomes?

A

any chromosomes that are not X or Y

3
Q

what are genes close together on the chromosome known as?

A

linked

4
Q

what are sex linked chromosomes?

A

those on the sex chromosomes

5
Q

what are alleles?

A

alternative forms of genes which have the same locus

6
Q

what are the types of alleles?

A

dominant
recessive
co-dominant

7
Q

what is epistasis?

A

non-allelic gene interaction

8
Q

what is incomplete penetrance of a gene?

A

gene is blocked by another

9
Q

what is variable expressivity?

A

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

10
Q

what mutation is responsible for short tales in Manx cats?

A

dominant M mutation

normal cats are mm

11
Q

what is an example of a gene with variable penetrance?

A

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

12
Q

what happens to Manx cats with MM?

A

die in utero as it is a lethal gene

13
Q

what is an example of epistatic gene interaction?

A

coat colour in labradors

14
Q

what does the 3 labrador coat colours result from?

A

differences in 2 gene loci that affect pigment expression

15
Q

how is labrador coat colour determined?

A

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

16
Q

what would an eebb larbrador look like?

A

yellow lab

brown nose, fur and lips

17
Q

how is tortoise shell coat produced in cats?

A

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.

18
Q

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

A

herding dogs

19
Q

what is the result of the MDR1 gene mutation?

A

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

20
Q

what protein is affected by the MDR1 gene mutation?

A

P- glycoprotein

21
Q

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

A

ivermectin
milbemycin
selamectin

22
Q

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

A

genetic testing

use of drugs that are not known to cause problems

23
Q

what genetic mutation is found in some greyhounds?

A

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

24
Q

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

A

no

25
Q

what do dog blood types represent?

A

genetically determined markers on the surface of the animals RBC

26
Q

what is antigenicity?

A

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

27
Q

what is the blood grouping system formed of?

A

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

28
Q

what blood type do around 70% of dogs have?

A

DEA 1+

29
Q

when can DEA sensitisation occur?

A

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

30
Q

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

A

transfusion history unknown
previous transfusion
previous transfusion reaction

31
Q

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

A

DEA 1 -

32
Q

what are the 3 blood types found in cats?

A

A
B
rare AB

33
Q

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

A

AB recessive to A and co-dominant to B

34
Q

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

A

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

35
Q

what is the most common blood type in cats?

A

A - 95%

36
Q

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

A

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

37
Q

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

A

type B has higher titre of anti-A antibodies

38
Q

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

A
Birmans, 
British shorthair,
Devon rex
Cornish rex,  
Ragdoll,
Turkish Angora, 
Turkish Van
39
Q

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

A
DSH, 
Siamese, 
Main coon, 
American shorthair, 
Bengal,
Norwegian Forest
40
Q

what is neonatal isoerythrolysis?

A

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

41
Q

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

A

Type B queen and type A/AB tom

type A is dominant

42
Q

what can be done to prevent neonatal erythrolysis in kittens?

A

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)

43
Q

what are kennel club screening programmes used to do?

A

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

44
Q

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

A

genetic test - for directly inherited diseases

screening tests - for more complex, slower developing issues

45
Q

how is hip scoring performed?

A

VD radiograph of pelvis hips and femurs

strict guidelines for positioning and identification

46
Q

how is a hip score supplied?

A

2 experts analyse images and score them

47
Q

what is the total hip score out of?

A

53 for each hip

106 in total

48
Q

what is a better hip score?

A

lower is better

49
Q

what is the issue with hip scoring?

A

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

50
Q

what is the elbow scheme designed to assess?

A

elbow dysplasia

51
Q

what radiographic view is needed for elbow scoring?

A

medio-lateral

52
Q

how is elbow dysplasia scored?

A

grade 1-3

if elbow scores are different the higher of the 2 is used

53
Q

what is involved in the Kennel Club eye scheme?

A

panel of ophthalmologists assess for 12 hereditary eye conditions

54
Q

how often is the eye scheme assessment renewed?

A

dogs should be seen every year while breeding

55
Q

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

A

6-12 weeks

56
Q

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

A

post breeding ~8 years old

57
Q

what eye conditions are screened for under the eye scheme?

A

glaucoma, lens luxation etc

evolving list as more conditions/breeds added to watch list

58
Q

what is Chiari malformation?

A

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

59
Q

what is Syringomyelia?

A

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

60
Q

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

A

MRI scans of at risk breeds

61
Q

what breeds are at risk of CM/SM?

A

cavalier king charles spaniels

griffon bruxellois

62
Q

at what age should screening for CM/SM start?

A

> 1 year old

63
Q

what breeds are assessed by the respiratory function grading system?

A

french bulldogs
pugs
english bull dogs

64
Q

how is the respiratory function grading performed?

A

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

65
Q

what are the respiratory function grades?

A

0 (clinically unaffected) -3 (severe)

66
Q

what is the aim of the heart screening scheme?

A

reduces chance of breeding puppies with MVD

67
Q

what dogs are involved in the heart screening scheme?

A

cavalier king charles spaniel

68
Q

what is assessed on heart screening?

A

murmur grade

mitral valve prolapse

69
Q

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

A

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

70
Q

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

A

murmur grade 0, 1, 2 or 3+

mitral valve prolapse - 0, 1, 2 or 3

71
Q

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

A

age at testing

72
Q

what is cat genetic screening used for?

A

planning breeding programmes

73
Q

what can only be detected in cats through genetic testing?

A

late onset diseases or carrier status (recessive allele)

74
Q

how are cat genetic samples obtained?

A

mouth swabs - ensuring cheek cells are collected no just saliva

75
Q

what can be screened for during cat genetic testing?

A

diseases
coat colour
blood types

76
Q

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

A

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

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