genetic disorders web conference [Repaired]

Genetics and Genetic Disorders
In
Beef Cattle
Discussion
Update Items
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Genetics vs Environment
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Genetics Refresher
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Currently Recognized Disorders
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Genetic Testing
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Implications for Purebred's
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Implications for Commerical
Genetic vs Environmental
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Environmental
–
–
Crooked-calf
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Lupine plant
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Manganese deficiency
Iodine deficiency
Two-headed calves
●
–
Genetic
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Prolapse
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Curly calf syndrome
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Hairless calves
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–
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Embryonic development
Prolapse
–
Angus, Red Angus,
Charolais
Hypotrichosis
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Hairless, Hereford
Genetic Refresher
Cattle = 60 chromosomes
Gametes (sex cells)
30 chromosomes female
30 chromosomes male
Genetic Refresher
Changes to DNA
Substitution – incorrect pairing
Insertion – extra nucleotide
Deletion – missing nucleotide
Frame Shift – enough changes in base pairs to alter amino acid coding
Genetic Refresher
Genetic Refresher
Genetic Refresher
WHAT IF I DON'T WANT ANY CARRIERS?
HOW CAN I DETERMINE
BB from Bb
WITHOUT MATING?
GENETIC TESTING
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PCR – polymerase chain reaction
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SNP's (snips) – single nucleotide polymorphisms
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PCR – florescent tags {B = red, b = yellow)
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GeneChip
–
Looks a many,many base pairs for multiple animals in a
single scan
–
50,000k and 100,000k chips
GENETIC TESTING
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●
●
Methods like PCR and Chips for detecting differences in
oligonucleotide sequences and SNPs has made genetic testing more
practical and less expensive.
Detection
–
Parentage testing
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Simple recessive traits (remove carriers from population)
Increase knowledge of complex traits and underlying mechanisms
–
Susceptibility to BRD
–
Feed efficiency
Genetic Disorders
●
●
Affect many breeds
Prone to come about through line breeding (a form of inbreeding to
increase the proportion of genes from a common ancestor).
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Angus probably gets most attention because of size of registry.
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Genetic disorders are often simple recessive
–
Few genes
–
Those that express the disorder usually don't make it into
production
Genetic Disorders
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Concerns
–
How many carriers are out there?
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How many calves are born with the disorder?
–
What does it mean if we have a large number of carriers
but a low proportion of expression?
Developmental Duplication
●
Latest genetic disorder in Angus
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Recognized in Australia
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Calves born with extra limbs
●
–
Remember this can be caused by embryo environment
Work of Jonathan Beever (U of Ill.) genetist found
commonality in genes associated with calves compared
to normal calves.
Developmental Duplication
(polymelia)
●
Genetic testing indicates 3% US sires are carriers
and a breed wide frequency of 6%.
Concern with carriers
●
Dd x Dd = 25% chance of dd.
–
Rare occurrence of developmental duplication
–
Embryonic death high among dd?
–
●
Increased PPI
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Increased conception to herd sire vs AI sire
Complication
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Incomplete penetrance
–
Animals that are dd but are not exhibit duplication.
Purebred Implications
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Discovery of dd animals that are expressing duplication
–
●
●
Is the situation more difficult than first thought?
Proactive to eliminate carriers from the breed (example known lethals like AM a.k.a.
curly calf)
–
Possible carriers flagged (ancestry)
–
Required testing (sells)
–
Required testing (registration)
–
Optional testing (remove pending condition from registry)
What about carrier bulls destined for commercial herds?
This animal has one or more ancestors known to carry a mutation that can result in calves
with a genetic condition known as Developmental Duplication (DD). Avoidance of mating
carrier animals is an essential component of managing the incidence of genetic conditions as
is the strategic use of DNA testing. AAA Statement of Certificate until confirmed by testing.
Commercial Implications
●
Little crossbreeding
–
●
Greater risk of developing female base herd with carriers
High degree of crossbreeding
–
Reduced risk of developing female base herd with
carriers
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Y1 calfcrop from: 1 bull [+-] x 25 cows [++]
–
- = simple undesirable trait
–
Kept 8 replacement heifers
●
●
4 [++] and 4[+-]
Y3 calfcrop from: 1 bull x 17 cows [++], 4 [++],4 [+-]
–
0.25 {chance of --} x 4 = 1
–
Herd level odds of negative result 1:24
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Y1 calfcrop from: 1 bull [+-] x 25 cows [++]
–
- = simple undesirable trait
–
Kept 8 replacement heifers
●
●
4 [++] and 4[+-]
Y3 calfcrop from: 1 bull [+-] x 17 cows [++], 4 [++],4 [+-]
–
0.25 {chance of --} x 4 = 1
–
Herd level odds of negative result 1:24
Probability of being a carrier = (0.5)n where
n = number of generations between offspring
and carrier ancestor - does not factor in number
of animals for herd level probability
Commercial Breeders
●
●
Crossbreeding helps avert risk.
Breeders that maintain a high percentage of certain
breeds should familiarize themselves with
recognized disorders and try to purchase free
genotypes (> 50% cattle sold are black).
Currently Recognized
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12 genetic abnormalities
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5 non-lethal, 7 lethal
–
11 have gene tests
UNL Publication G2055
Testing
●
●
Companies (order forms and testing online)
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GeneSeek (Neogen subsidiary)
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Igenity
–
Zoetis (used to be Pfizer)
Cost
–
Most $24/condition
–
Some discount samples > 50 ($2.00)
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