Genetics Flashcards
(159 cards)
1
Q
The skills of animal breeding lie in:
A
Knowing what changes will be worthwhile, correctly and efficiently identifying the genetically superior animals, identifying the most genetically and economically efficient way of mating the selected animals
2
Q
One of the basic requirements for effective selection program?
A
There must be genetic differences between animals in order to make genetic improvement. Genetic Variation.
3
Q
What is genetic variation directly linked to?
A
Heritability. If there is high heritability (>25%)- then selection will be effective in improving the genetic composion, moderate heritable 10-25%- possible but slower and harder to achieve, low heritability < 10%- difficult since there are only small genetic differences between animals
4
Q
Where there are unfavorable correlated responses (e.g. productivity and fertility), how do you approach this?
A
Develop a selection index that optimizes overall response in the two or more trains of interest OR you can develop separate lines that excel in one or a few compatible traits… For example, develop terminal sire lines and maternal lines– terminal sire line in meat selected for larger size and good carcass attributes, while the maternal lines for reproductive rate and feed efficiency
5
Q
What to account for to maximize efficiency:
A
cost of measurement of teach trait, number of animals to be measured, rate of dissemination of improved genes
6
Q
What are estimated breeding values?
A
Phenotypic measurements. Estimationof breeding value based on an animal’s phenotype alone can be quire accurate for highly heritable traits. However, animals need to be compared across flocks and genetic and environmental influences need to be disentangled.
7
Q
What is Best Linear Unbiased Prediction (BLUP)?
A
More sophisticated statistical model, BLUP uses all available information about an animal’s breeding value, including data on related animals
8
Q
What are the two most important limiting factors in a breeding program?
A
Reproductive rate of breeding animals and uncertainty about their true genetic merit
9
Q
What are common investments in breeding programs?
A
Trait measurement and genetic evaluation and to technology used to increase reproductive rates
10
Q
Animal breeding in a nutshell
A
Where to go–> breeding objective–> how to get there (velocity)–> trait measurement (which traits, which animals, males v. females, progeny test), EBVs (phenotypes, pedigree, BLUP, genetic markers), reproductive technology–> Selection/ Culling/ Mating
11
Q
What are the problems with British bulldog breeding?
A
Skull should be very large- larger the better- dystocia, fetopelvic disproportion
12
Q
What are the problems with Dachshunds?
A
The whole trunk should be long; prolapsed intervertebral disc
13
Q
What are the problems with miniature poodle?
A
“fine legs”– fractures
14
Q
What are the problems with pugs breeding standards?
A
Eyes very large globular in shape- exopthalmus, keratitis
15
Q
What are the important aims for a breeding objective?
A
Focused, quantified, timelined
16
Q
What is a breeding objective?
A
Provides the direction for the whole program by defining the set of characters that we wish to improve by breeding. The more trains one attempts to improve, the less progress will be made in any single trait.
17
Q
Response to selection- quantative genetics equation
A
R= (((im x rm) + (if x rf))/ (Lm+Lf))* SDG i= intensity r= accuracy genetic SD L= generation interval
18
Q
For cattle and sheep, a well designed breeding program should deliver what percentage of improvement annually?
A
2% (22% over 10 years)
19
Q
How are quantative trais determined?
A
Combined action of many alleles at many loci, most of which have a small effect. Minimum 30 genes for all traits.
20
Q
Non-genetic factors equation?
A
P= G+ E P= phenotypic value- the performance of an individual in relation to a particular character G= genotypic value- the avg. performance of a particular genotype (determined at conception) E= Environmental deviation (either +ve or -ve)
21
Q
What does inferior recessive alleles mean for future generations?
A
An animal may have fabulous genotypic value- but it may have many more inferior recessive alleles that may have no effect on itself but will affect a population of offspring
22
Q
What is the genotypic value equation?
A
G= A+D+I A= breeding value (additive effect) D= dominance (+ ve or - ve) I= Epistasis (interaction between genes) D and I depend on the arrangement of genes within a genotype, breeding value does not.
23
Q
Phenotypic value equation?
A
P= A+D+I+E
24
Q
What are you trying to do when selecting animals for breeding?
A
Trying to increase the frequency of favourable genes
25
EBV?
Series of clues of the true breeding value- clues come from progeny testing or the animal's own phenotypic performance or the performance of other relatives or genetic tests or preferably a combo of all available clues
26
How are EBVs expressed?
Deviations from the mean value of a reference population
27
How do you combine all these EBVs to pick the "best" animals?
Weighting each EBV by economic value and summing the lot up-- Index selection (always more efficient than alternative methods of integrating the information)
28
What is an animal's breeding value (A)?
Not the same as genotypic value. Breeding value is directly proportional to the number of favourable genes- genotypic value depends on the arrangement of those genes.
29
What is heratability (h^2)?
The proportion of the phenotypic variance attributable to variance in breeding balues. OR the proportion of phenotypic superiority (inferiority) of parents that is seen in their offspring).
30
What is the equation for heritability?
h^2= Va/Vp, Variance of breeding value/ variance of phenotypic value. h^2 must be between 0-1, if it is 0 then breeding value makes no contribution to Vp thus genetic progress is not possible in this trait.
If it is 1 then the observed variation in the trait would be due to variation in breeding values alone- no such case exists. (the higher, the more rapid the genetic progress possible)
31
What is a small heritability?
Less than 0.10 are small- consider non-genetic methods of improvement. Fertility and reproductive traits tend to have small h^2.
32
What is a large heritability?
More than 0.30 are large. Product quality traits tends to have a large h^2- fibre diameter, wool, protein, milk, marbling
33
What has moderate h^2 (0.2 approx)?
Growth, body weight
34
How is heritability measured?
By measuring the performance of many offspring of parents with known performance- deviation from mean performance is the measure
35
How is heritability estimated?
Using information from all forms of relationships- offspring, half-sibs, full-sibs. Sophisticated algorithm called REML is used for this purpose.
36
Predicting response to selection- aiming for largest possible response to selection program- what is genetic variance?
A measure of the variance in additive genetic values within the population of animals. Heritability is a normalized indicator of genetic variance. The greater the genetic variance, the greater the potential for improvement.
37
What populations will have less genetic variance?
Inbred populations, small populations, highly selected populations
38
What is accuracy?
Series of clues EBVs- because true acuracy is unknown (A)- ranked according to EBV- weighted- and then selected.
39
How do you improve accuracy?
Moving from visual to direct measurement, accounting for environmental factors, measuring correlated traits, repeat measurements, progeny testing, accounting for performance of other relatives, utilization of genomics..... if accuracy is poor, all EBVs will be close to zero.
40
What is G X E interactions?
When the genetic ranking of an individual is different in different environments. e.g. Dairy industry USA EBVs vs. Australian EBVs.
Disease, climate, and management variations may contribute to GxE interactions- adaptation of genotypes to particular conditions. Selection for performance is generally most effective if it takes place in an environment similar to that of the enterprise
41
What is meant by genetic correlation between traits?
Selection for one character almost always produces a change in another character. Some expected, some unexpected.
42
What is a phenotypic correlation?
The extent to which two traits are phenotypically related- phenotypic and genotypic correlation for the one set of traits can be very different. i.e. strong phenotypic correlation between bodyweight and fleeceweight but no genotypic correlation
PHENOTYPE INCLUDES GENES AND ENVIRONMENT
43
What is repeatability?
The correlation between any two measurements of the same character on the one individual. For example, repeatability of most production traits is quite high, if an animal has superior phenotypic value (milk yield for example) in its first measurement it is highly likely to be superior at later measurements- no need to measure again
44
What are some considerations of progeny testing?
Progeny testing a very large number of progeny is the most accurate method of estimating breeding values, but detrimental increase in generation interval often outweighs the accuracy benefit- resulting in a reduction in genetic response--> accurate EBVs should exist before widespread industry use of any sire/dam
45
What is pedigree selection?
Selection based only on performance of ancestors. Common in horses. Never as accurate as mass selection. Remote ancestors next to useless. Only sensible when selection has to be made before candidates performance can be measured.
46
What is genetic marker assisted selection?
Need numerous markers to improve accuracy of selection for any given trait- not one or two. Requires sacrifice of the animal. Full panel of markers for all important traits would potentially have very large impact by reducing generation interval (early, accurate selection)
47
How do we combine every bit of information we have to get the most accurate information?
BLUP
48
What is BLUP?
Best Linear Unbiased Prediction, sophisticated statistical model widely used that combine all available clues to obtain the most accurate EBV possible. Increasing accuracy gives more spread in EBVs- ranking of animals genetic merit will be improved. Also allows measurement of genetic progress over time- by monitoring progeny.
49
What is the range in average generation interval in sheep flocks?
Slow turnover flocks- ewes lamb for the first time as 3yo, sold as CFA as 7yo- rams 2-5 yo (avg. L= 4.11 years)
Rapid turnover flock- ewes lamb at 2yo- CFA(cast for age) as 5 yo- rams 2 & 3 yo only (avg. L= 2.97 years)
50
What is selection intensity?
A measure of the expected superiority, in standard deviations, of the selected animals. Varies inversely with the proportion of candidate animals that are selected for breeding. If 100% of animals are selected for breeding, there is zero selection intensity, as p (phenotype) increases, I (epistasis- interaction between genes) increases.
51
What are some influences on selection intensity?
Fecundity, fertility- more fecund- greater intensity possible. Most mammals- the rate and direction of genetic progress largely driven by male selection. Im >> If
52
What is the aim of MOET?
Improve female fecundity (actual reproductive rate of an animal) and thus selection intensity in females
53
Since Im >> If, what does this cause on commercial farms?
Breed female stock; buy males in
54
How does selection intensity change as proportion selected decreases?
Selection intensity increases
55
What are the two major problems with small population size?
Inbreeding and genetic drift
56
What is an effective population size?
Only those who contribute to the next generation genetically (not their actual census size). Ne
57
What is determined by the effective population size?
Determines the rate and impact of negative genetic processes
58
Why is Ne less than N?
Unequal sex ratio, population subdivision, non-random mating, other factors
59
What is Ne in a seal colony with 4 adult males and 100 breeding females?
(4 (4*100))/ (4+100)= 15.38
60
What does inbreeding result in?
Decreased performance (inbreeding depression)- possibly present as poor reproductive performance, Increased homozygosity (reduced heterozygosity) in the population- increase in incidence of recessive genetic disorders
61
How do you measure inbreeding?
Inbreeding coefficient needs to stay below 1%, preferably below 0.5% per annum. Generally for every 1% increase inbreeding coeffecient, 1% decrease in reproductive traits occurs. 1% per annum increase inbreeding coefficient can almost negate any genetic progress from selection.
62
What does the effective population size need to be in order to keep the inbreeding coefficient below 1%? How about 0.5%
50/L (L= avg. generation interval). 100/L to keep it below 0.5%
63
How many lethal recessive alleles does any normal animal carry?
About 20 lethal recessive alleles
64
What is genetic drift?
Changes in allele frequency due entirely by chance. Genetic drift may cause gene variants to disappear completely and therefore reduce genetic variation. Results in decreased response, plateauing of response, variation in response. Ne should always be greater than 50/L preferably greater than 100/L
65
What are the main points to discourage inbreeding?
1. Encourage the use of outside genetic material (closed studs are at highest risk)
2. Ensure the effective population size is at least 50/L to avoid the worst of genetic drift and inbreeding
3. Avoid mating very close relatives, full sibs, parents and offspring, half sibs
4. Use of males often key (at least 5 males required)
66
What are autosomal recessive disorders?
Tend to be enzyme deficiencies- may skip generations, all offspring of two affected parents are affected, approx. equal numbers of males and females affected, approx. equal number of males and females affected. Best way to control- control inbreeding.
67
What are autosomal dominant disorders?
Defects in non-enzyme polypeptides- i.e. polycystic kidney disease (cats); dominant epidermis bullosa (dogs). Transmitted from generation to generation without skipping. Except for new mutant, every affected offspring has at least one affected parent. Normal offspring from affected parent produce only normal offspring.
68
What are X-Linked Recessive disorders?
X-linked tremor of dogs; cone/rod dystrophy in miniature dachshunds etc. Disorder may skip generations, all offspring of two affected parents are affected. Affects males more than females.
69
Multi-factorial genetic diseases?
Hip dysplasia in dogs, PDA in many species, bloat in cattle, osteochondrosis in horses, glaucoma in setters. Combined action of alleles at numerous loci.
70
What are the two main advantages of cross breeding?
Hybrid vigour and complementarity
71
What is heterosis?
D+I
D= dominance (+ ve or - ve)
I= Epistasis (interaction between genes)
D and I depend on the arrangement of genes within a genotype, breeding value does not.
Heterosis is due to non-additive genetic actions (D and I)\
In general, the greater the genetic difference in the strains, the greater the heterosis. Heterosis is greatest for traits associated with reproduction and viability.
Hybrid Vigor- hybrid vigor is a once off- they are not passed on to progeny of the cross- bred animals- and for commercial harvesting continuous crossing is required
72
Which is greater maternal heterosis or paternal?
Generally maternal heterosis > paternal heterosis e.g. milk yield, mothering
73
What is a four way cross?
AB female + CD male --> (AB)(CD)
Exploits advantages of heterosis to the greatest extent
But is also the most difficult to maintain because you need purebred A B C and D-- need crossbred AB and CD, need all to be genetically improving.
74
What is a three way cross?
AB female x C male --> (AB) C
| Exploits maternal and individual heterosis (and potentially, complementarity)
75
What is a two way cross?
A x B--> AB
| Exploits individual heterosis alone- complementarity may also exist
76
Two way rotational?
2 breeds; one mating rule; never mate females to the same breed as their sire-- often best option as easiest and you get almost as much benefit as three way
77
What is introgression?
Introducing a new gene into a breed
78
What is grading up?
Breed substitution- used for rare or exotic breeds to build up "purebred" numers
79
How do you close off an autosomal recessive strain?
All with phenotype will have it. DNA markers would be great.
80
How do you close off an autosomal dominant strain?
More difficult than autosomal recessive. Arrange test mating and cull carriers. DNA markers would be great. Is there a correlated trait?
81
What might new technologies do?
Increase intensity, increase accuracy, or reduce generation intervals
82
What does AI do?
Increased selection intensity of male (enables use of 1 in 1000 ram instead of 1 in a 100-sourcing from the world population), potentially incrased accuracy of EBVs, potentially increases effective population size, but costly and watch for inbreeding
83
How does AI increase EBV accuracy?
Increased male selection intensity, allows increased accuracy of EBVs by progeny tested, more measurements. Do not use semen from innaccurate EBV estimates. Beward- GxE interactions become prevalent.
84
How has AI helped the dairy industry?
Large genetic gains from 0.5% to 1.5% per year and is relatively low cost
85
Higher cost AI in what industries?
Beef (oestrus synchronization required) and sheep (because not enough profit margin and naturally mated rams are efficient, except AI can pay on merino studs in open flocks not closed)
86
Why not AI all females to one magic male?
All animals carry deleterious genes; above average in 20 traits- one in a million, inbreeding, closed flocks/herds need at least 5 males to avoid substantial loss from inbreeding
87
What are some industry benefits of AI?
Create genetic links for benchmarking, reduce genetic lag between tiers, rapidly disseminate new genetic material, potentially the global population becomes the one herd/flock (but beware of Gx E)
88
With Multiple Ovulation and Embryo Transfer?
Increase selection intensity of females, Potentially increased EBVs, but high cost and inbreeding must be avoided
89
What does MOET require?
Accurate ID of superior females (often does not occur), substantial improvements in rate of genetic gain possible in optimized systems (70% increase in beef; 50% increase in sheep)
90
What are some MOET mistakes?
Inbreeding a major problem- increased number of males, MOET scheme missing, use fresh semen rather than genetically superior semen, use females that harvest well rather than females of high genetic merit
91
Cloning
Asexual reproduction- share common nuclear DNA
92
Cloning with genetic improvement?
Potential to quickly disseminate genetically superior animals to commercial producers (close the 10 year gap), not for use in studs/ nucleus as genetic variation essential
93
What is breeding value?
Value of an animal's genes to its progeny.
94
What is genetic value or genotypic value?
Value of an animal's genes to itself. For when we want to select animals to make clones of themselves to generate product to be harvest.
95
Genetic engineering- transgenic animals
Introducing foreign DNA into genetic DNA code to gain new knowledge, decipher genetic code, study physiological systems, build genetic disease models, improve animal production trains, produce new animal products
96
With a breeding coefficient of 0.95% per annum you should:
Bring in external genetics from unrelated individuals
97
To increase the accuracy of EBVs of 400 day weight gain of a bull's offspring you can?
Include data from bull's parents and siblings and include 200 day weight data from the bull
98
A female cat presents with a genetic disorder which is controlled by a single gene. You know that this disorder is not seen in the mother, the maternal grandmother or the father. This disorder is most likely:
Autosomal recessive
99
Heterosis is?
A result of non-additive genetic actions (D+I)
100
The value for hertitability is between
0 and 1
101
If you decide to cross breed two pigs a Large White sow and a Duroc boar- what would you expect from this cross?
Both male and female offspring will display advantages of heterosis
102
Why does inbreeding result in an increase in genetic disorders?
An increased chance of inheriting the same allele of a gene at a given loci.
103
In order to observe rapid genetic progress when selecting for a trait, it is desirable that the trait be
Highly heritable and highly variable within the population
104
What are breeds?
Often based on animals that have been selected for particular phenotypic traits
105
What does the effective population size determine?
Determines the rate and impact of genetic drift
106
How do you eliminate an autosomal dominant disorder from a population?
Cull from the breeding population all animals displaying the disorder
107
Which animal enterprise groups most likely use AI as a major part of their breeding program?
Pig production, dairy cattle, and nucleus Polled Dorset stud
108
EBV for fibre diameter for a ram is -2.0 microns. What would be the expected difference in fibre diameter (reduction) of the progeny's fleece if you were to mate your ewes to the ram?
-0.8 microns
109
What is heretability?
The proportion of phenotypic variance attributable to variance in breeding values or: the proportion of phenotypic superiority (inferiority) that is seen in offspring
110
What is genetic correlation?
the extent to which two traits are genetically related
111
What is phenotypic correlation?
The extent to which two traits are phenotypically related
112
What is a phenotype?
The composite of an organism's observable characteristics or traits. Expression of an organisms genes and environment- and the interaction between the two.
113
What is a genotype?
An organism's inherited instructions it carries within its genetic code.
114
With a phenotypical correlation of 0.4 between two traits, and one trait is part of the breeding objectives, how rapid would genetic progress be made?
With this information, progress would not be made because we would need to know their genetic correlation and the traits would need to be part of the breeding objectives and using males from a stud along the same lines.
115
Farm management useful to control the mastitis problem.
1. farm profile- how big, how many cows, type of milking machines, cow age profile
2. milk cultures- does the farm have bacterial cultures from cows that have had mastitis
3. Individual cow cell counts- ICCC- does the farm have ICCCs and what percentage are over 250,000? What age cows seem to be having problems? when do they occur?
4. Milking test machine- is it working properly? Otherwise can damage the end of the teat and lead to mastitis
5. Performance test milking machine
6. Milking routine, teat cup slips- what happens during milking, how are cows handled, are there any teat cup slips (sign there is a problem with the milking machine)
7. Clinical cases- how many clinical cases does the herd have, when do they occur, what causes them
8. Teat condition- check it, particularly teat orifice for any damage
9. Cow behaviour- milking time per cow, do cow look happy in the dairy
10. Milking cluster alignment- cow udders should be milked out evenly
11. teat disinfectant- how is it applied, is it made fresh, to the right concentration, emolient and is this at the correct concentration
12. environment- what is the entry, waiting area and exit to the dairy like- dry, muddy, covered in deep faeces, etc.
116
At what level of bulk milk cell count is there considered to be a problem with mastitis on dairy properties?
250,000 is the level at which there is considered to be a problem. Four most recent tests- 192,000; 216,000; 241,000; 245,000- have no reached but very close.
117
What percentage of the herd having evidence of mastitis over the dry period would be a problem?
> 10%. There is an excess in first calving animals. The actual rate = 25% and the trigger threshold = 15%. The problem months are August and February according to graph.
118
If your herd has 4/100 cows in milk per month with new infection rate, is there a problem?
No but it is close, as >5/ 100 is when there is a problem.
119
What further info or testing should the farmer do to decide if they should treat the cows with antibiotic during lactation? How should this antibiotic be chosen, what is the most likely route of administration? Why is it the most likely route?
Culture and sensitivity testing of the organisms causing the mastitis. Select an antibiotic to which the organism is sensitive (i.e. not resistant). Most likely route of administration is intramammary via the teat canal. Efficient at achieving effective concentrations at the site of infection.
120
What are four things the farmer might be able to do to ensure that any mastitis problems are reduced.
Treat the herd with "dry cow therapy"- antibiotic at drying off time at the end of the season. Cull persistently or repeatedly infected animals from the herd (reduces herd cell count and risk of infection to other animals). Undertake occasional herd testing to measure individual cow cell counts. Improve hygiene in the milking shed- milkers wearing gloves, and post-milking teat spraying of cows with disinfectant.
121
What is Vp?
Observed variation in a trait (Vp). Vp= Va+Vd+Vi+Ve. Variation in a trait is required if genetic progress is to be made. Genetic progress can only be made if Va (variability of breeding value) is a significant contributor to the observed phenotypic variation.
122
How do you "get there" with breeding objectives? Velocity?
Trait measurement (which traits, which animals, progeny test), estimation of breeding value (phenotype, pedigree, BLUP, genetic markers), reproductive technology
123
What is MOET?
Embryos are placed in the uterus of a female. Like IVF. Fresh or frozen.
124
What is the aim of a breeding objective?
Expected improvement will bring the greatest expected future benefit and profit.
125
Who can have a greater improvement than 2% per annum?
Hens because they can produce 150 progeny within a year. So 4%+ per annum consistently achieved in broiler industry.
126
In P= G+ E, what is P?
Phenotypic value- the performance of an individual in relation to a particular character. Usually expressed as a deviation from mean performance.
127
In P= G+ E, what is G?
Genotypic value- the average performance of a particular genotype (determined at conception). An animal may have many more inferior recessive alleles with no effect on itself but willa ffect a population of offspring. Why you have EBVs and test progeny- and look for greater accuracy.
128
In P= G+ E, what is E?
Environmental Deviation (either + ve or - ve)
129
How can genotypic value be further broken down?
G= A+ D+ I
130
In G= A+ D+ I, What is A?
Breeding Value (ADDITIVE EFFECT). NOT dependent on the arrangement of genes.
131
In G= A+ D+ I, what is D?
Dominance (+ve or -ve). DEPENDENT ON THE ARRANGEMENT OF GENES
132
In G= A+ D+ I, what is I?
Epistasis (interaction between genes). DEPENDENT ON THE ARRANGEMENT OF GENES.
133
What do breeding programs aim to improve?
(A) Breeding Value. The mean value of an animal's genes to a large population of offspring. NOT the same as genotypic value (A+D+I). Because genotypic value also takes into account the arrangement of genes- dominance and epistasis (interaction between genes).
134
What is breeding value (A)?
Determined by the sum of the effects of all alleles at all lovi that affect the character. A is defined as TWICE the avg. performance of offspring produced by mating that animal to a random sample of animals, expressed as a deviation from the population mean. The breeding value of a heterozygote is exactly midway between the breeding value of two relevant homozygotes. When selecting animals for breeding, we are doing nothing more than trying to increase the frequency of favourable genes.
135
How do you quantify A?
EBVs. True A is unknown. But we have "Clues" of the true breeding value. EBVs are expressed as deviations from the mean value of a reference population.
136
What are EBV weaknesses?
While EBVs provide the best basis for the comparison of the genetic merit of animals reared in different environments and management conditions, they can only be used to compare animals within the same breed. (different breeds have different bases and are subject to different rates of change over time). The differences in EBVs between animals are more important than the absolute value of the EBV.
137
What are some GOOD negative or small to moderate EBVs?
Days to Calving, Gestation length, small or moderate birth weight EBVs + 2.0 kg vs. + 6.0 kg (+2.0 kg would have lower risk of a difficult calfing). In dairy, smaller or moderate mature cow weight wanted because lower feed requirements, FEC is good when it is negative, Fibre Diameter
138
What are two maternal traits?
Milk production and mature cow weight.
139
How do you choose the best male from EBVs?
Index selection. Weight each trait by its future economic importance.
140
What else are EBVs used for?
To estimate the performance of offspring from a candidate animal
141
A group of selected bulls with a mean EBV for 150 day wt. of +20 kg are going to be joined with a group of selected cows with a mean EBV for 150 day weight of + 2 kg. What is the expected improvement in 150 day weight of the progeny when compared to progeny from average cows and bulls?
Y= growth of the rate of the average progeny
Y+ (20+2)/2= Y + 11 kg
Y+11-Y= 11 kg (don't need to know avg. to work it out)
142
A farmer is considering purchasing a bull with a 400 day weight EBV of +40 kg or a cheaper bull with a 400 day weight EBV of 10 kg. She does not know the mean EBV of her own cows. What is the expected improvement in 400 day weight of the progeny between the expensive and less expensive?
Let the mean EBV of her own cows = X
(40+x)/2= expected 400 day weight of more expensive bull
(10+x)/2= expected 400 day weight of progeny from cheaper bull
((40+x)-(10+x))/2= 30/2= 15 kg
ALWAYS HALF THE DIFFERENCE IN MALE EBVS
143
What is Vp?
Observed variation in a trait.
Vp= Va+Vd+Vi+Ve
Variation in a trait is required for genetic progress to be made.
Va is a significant contributor to the observed phenotypic variation.
144
What is the equation for heretability?
Va/Vp. Which means variance in breeding value divided by variance in phenotype.
The proportion of the phenotypic variance attributable to variance in breeding values.
The closer to 1, selecting on observed performance would be a perfect measure of the genes the animal is carrying and would result in rapid genetic progress.
145
How is heretability measured?
Most directly, by measuring the performance of many offspring of parents with known performance. Deviation from mean performance in the measure. Sophisticated algorithm- REML- estimates from all forms of relationships.
Va and Vp might different in different populations/ environments, it is not surprising that estimates for h^2 differ for the one trait.
(the proportion of phenotypic superiority (inferiority) of parents that is seen in offspring)
146
What is the standard deviation of genetic variance in the response equation?
A measure of the variation in additive genetic values within the population of animals. The greater the genetic variance, the greater the potential of improvement. We aim to maximize response to our selection program.
147
What happens when improving accuracy?
Often comes at a cost- including increasing generation intervals? Properly designed program needed.
148
How do you work out accuracy mathematically based on a single measurement?
Square root of heritability. H^2. So fibre diameter has a heritability of 0.5. therefore estimating EBVs for fibre diameter based on a single measurement of fibre diameter from all candidates has an accuracy 0.75. As heretability goes down, accuracy goes down.
149
What is Gx E interactions?
Disease, climate, and management variation contribute. Adaptations of genotypes to particular conditions. Selection for performance is most effective if it takes place in an environment similar to that of the enterprise.
150
What is correlation between traits?
Selection for one character, almost always produces a change in another character. Some expected, some unexpected. example) Russian foxes selected for tameness as cubs- successful- but coat colour changes occurred too. Genetic correlations.
Have a domain between -1 and 1. Should be accounted for in selection programs. For example, high genetic correlation between CFW (clean fleece weight) and FD (fibre diameter).
151
What is genomic selection?
Looking at numerous "markers" to improve accuracy of selection for any given trait. When this is possible will allow for early and accurate selection. Would reduce the generation interval.
152
What is a generation interval?
The average age of both of the parents when the children were born. The shorter the generation interval, the faster the rate of genetic progress per annum resulting from selection.
Genetic interval is influenced by reproductive rate, morality rates- poor performance in either- longer generation interval
153
When do ewes lamb? When do beef cows calve? How long are rams and bulls used?
ewes lamb from 2 to 7 yo; beef cows calve from 2 to 15 yo; rams and bulls used typically for 2 to 4 years
154
What is a slow turnover flock?
3 yo ewe lamb, and CFA at 7. Rams used 2, 3, 4, 5yo
155
What is a rapid turnover flock?
Ewes lamb at 2 yo, all ewe sold as CFA as 5 yo. Rams used at 2 and 3yo
156
Avg L?
(Lf+Lm)/ 2
Lm is number of males x age + 2yo x number + etc. divided by total number
Same with females.
157
What is selection intensity?
A measure of the expected superiority, in standard deviations, of the selected animals. Varies inversely with the proportion of candidate animals that are selected for breeding.
If 100% of animals are selected for breeding, there is zero selection intensity. As p decreases, I increases.
158
How large would a closed sheep stud have to be to keep the inbreeding coefficient from increasing at 0.5% per annum? Assume rams are mated at 2% (M= 0.2 F). Assume the average generation interval of the stud is 4 years.
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To keep inbreeding coefficient from increasing at less than 0.5% per annum.
Ne> 100/L
L=4
Ne>25
4* (M*F)/(M+F)>25
But M= 0.2F
4*(0.02F*F)/1.02*F > 25
0.08F/1.02 > 25
0.08F > 25.5
F>318
```
Need a closed flock with at least 300 ewes and 6 rams to keep inbreeding under control. Or open the population to outside genetic material. Males usually the key. AI or buy males from genetically diverse populations.
159
What is an example of a widely used sire that caused an autosomal recessive disease to take hold in a population?
Hemophilia in German Shepherds.
