Genetics and Breeding:
Konsep Dasar, Interval generasi
dan Respon
Seleksi
PENGERTIAN DASAR SELEKSI
DEFINISI SELEKSI :
1.Perbaikan mutu genetik ternak melalui perubahan rata-rata fenotip populasi agar lebih menguntungkan secara ekonomis
2. Memilih ternak untuk bibit pada generasi berikutnya CARA :
1. Eksploitasi variabilitas genetik/fenotip Antar bangsa/populasi
Dalam bangsa /populasi
TAHAPAN:
1. Pemilihan/penentuan tujuan 2. 2. Pemilihan metode seleksi
TUJUAN :
Sebuah karakter/kombinasi beberapa karakter yang ingin diperbaiki (tidak harus dapat diukur pada individu yang bersangkutan)
DASAR SELEKSI: INFORMASI
PERFORMANS
•
Individual selection:
selection of individuals based on their
own phenotypic values (also called mass selection).
•
Family selection:
whole families are selected or rejected
based according to the phenotypic mean of the family (we
select the family with the largest mean). This method is
preferred when the heritability of the trait is low. But the
efficacy of this method is reduced when the environmental
variation common to the members of the same family is large.
• Sib-selection and progeny testing are family-selection
methods.
•
Within-family selection:
the best individual in each family is
selected. The main case in which this method has an advantage
is when there is a large common environmental variance.
Seleksi berdasar Sumber Informasi
: 1. Seleksi individu: catatan individu ybs untuk evaluasi ybs- pada sapi perah/potong : kurang tepat meramal produksi
(perlu h2 tinggi untuk seleksi efektif) - estimasi produksi individu : dasar NILAI PEMULIAAN (NP)
NP : h2 ((Performan Indv- Rata-rata Performans Pop) 2. Seleksi pedegree (silsilah):
dasar catatan tetua/nenek moyang
dipengaruhi derajat inbreeding (jauh dekat kekerabatannya
3. Uji Kolateral:
Berdasarkan catatan anggota keluarga Ketepatan tergantung h2, Ripitabilitas.
4Uji Progeni: - . pada pejantan dan informasi prod anak Dasar : anak adalah contoh acak genotip orang tua Contoh : sapi 4.5 – 5.0 tahun.
Selection Response
• Selection response is the expected rate genetic change (genetic progress or
improvement) which results from selection.
• The effectiveness of selection is measured by the rate of genetic change
achieved.
•
Selection intensity (
i
)
is the selection differential
expressed in standard deviations.
•
Selection differential (S):
the difference between the
mean selection criterion of selected animals and the
mean selection criterion of all potential parents.
•
Selection criterion (SC):
the information on which we
base selection (breeding value, phenotypic value, etc).
Selection intensity increases as the proportion selected is
reduced
With phenotypic selection (individual selection or
mass selection) the formula for selection response
can be expressed as:
L
S
h
L
i
h
L
hi
G
A
P
2
2
Generation Interval
• Generation interval is the amount of time
required to replace one generation with the next.
• More practical definition:
the average age of
parents when their offspring are born.
• (rataan umur tetua pada saat anak-anak lahir,
kelahiran 1,2,3, dst
)
• As the generation interval increases the rate of
genetic change is reduced.
Average generation interval
Species
Male
Female
Cattle
3 to 4
4.5 to 6
Sheep
2 to 3
4 to 4.5
Swine
1.5 to 2
1.5 to 3
Horses
8 to 12
8 to 12
Chickens
1 to 1.5
1 to 1.5
.
lahir kawin beranak
1 2 12 bln 1 bln
Selection intensity, generation interval and the additive variance may
differ between males and females.
EXAMPLE 1:
Suppose we select for six-month weight in lambs based on phenotypic values. If the average of all candidates for selection is 32 kg, the phenotypic standard deviation is 4 kg, the generation interval in sheep is three years and the heritability of six-month weight is 0.40, suppose also that the average of selected parents is 42 kg. Find: 1. The intensity of selection2. The expected selection response per year.
Solution:
year
kg
L
S
h
G
S
i
P/
33
.
1
3
)
32
42
(
40
.
0
5
.
2
4
)
32
42
(
2
EXAMPLE 2:
Phenotypic selection for yearling weight in beef cattle.Bulls: keep the top 3% Cows: keep the top 50%
Suppose heritability is 0.40, generation interval is 5 years for bulls and 6.5 years for cows and the additive genetic variance is 1225 in both sexes. Find the expected selection response per year.
year
lb
G
h
accuracy
/
9
.
5
5
.
6
5
)
35
)(
80
.
0
(
63
.
0
)
35
)(
27
.
2
(
63
.
0
63
.
0
40
.
0
2
Example:
suppose we are selecting dairy bulls for improving
milk yield using progeny testing and we are using the top 5% of
bulls with average accuracy of 0.90. What is the expected genetic
change in fat% given that the genetic correlation between milk
yield and fat% is –0.50, the heritability of fat% is 0.50 and the
phenotypic variance for fat% is 0.80. Suppose also that the
generation interval is 6 years.
year
G
L
h
i
X Y Y Y A x Y/
%
098
.
0
6
)
632
.
0
)(
06
.
2
)(
90
.
0
)(
50
.
0
(
6
,
632
.
0
)
80
.
0
)(
50
.
0
(
,
06
.
2
/ 2 2
Selection for multiple traits
•
So far we have dealt with selection for a single
traits. However, in practice we may want to
improve several traits.
•
There are three methods of selection for multiple
traits:
1.
Tandem selection
2.
Independent culling levels
3.
Economic selection index
METODE SELEKSI:
1. Tandem : secara berurutan
cara : 1 sifat selesai diteruskan sifat kedua waktu yang diperlukan panjang
untuk sifat yang tidak berkorelasi positif
2. Independen Culling Level:
ditentukan batas produksi tertentu, jika kurang dari batas minimal maka dilakukan culling/afkir
kekurangan: tidak ada kompensasi untuk sifat-2 yang unggul
3. Indeks : metode terbaik
menghitung indeks beberapa sifat yang diseleksi perlu banyak data
Tandem Selection
• In this method we begin by selection for one trait,
after several years we start selecting for the second
trait and so forth until the desired level of
improvement is reached .
• This method is not efficient:
- it takes long time
- if unfavorable genetic correlations exist between
selected traits, selection for one will negatively affect
one or more of the other traits.
Independent culling levels
• A standard (a culling level) is set for each trait.
• Selected animals should meet the standard for each
trait.
• Any animal which does not meet the standard of any
one of the traits is culled even if it is excellent for one
or more of the traits.
• Faster than the tandem method, but it is very strict
(may cause culling of excellent animals for one trait
which do not meet the standards for other traits).
Selection Index
• Combines information on several traits in a
single index using weighting factors.
n n
P
b
P
b
P
b
I
1 1
2 2
...
...
Where :- b1, …………,bn are weighting factors (partial regression coefficients) - P1: information on trait 1
. . .
Advantages
• More efficient than tandem selection and independent
culling methods.
• It takes into account the genetic correlations between
traits.
• It takes into account the economic value for each
trait.
• An animal’s excellence in one trait can compensate
for its weakness in another trait.
Kemajuan Genetik Karena seleksi
berdasarkan nilai intensitas seleksi
Contoh: Sapi
Populasi sapi lahir/thn = 8000 ekor, sex rasio 1 : 1
Jika diseleksi (kawin alam ) = 3000 pejantan Proporsi terseleksi = 3000/4000 = 0,7 Intensitas seleksi (i =tabel) = 0.42
Atau (program breeding), diseleksi 1000 pejantan Proporsi terseleksi = 1000/4000 = 0.25 Intensitas seleksi (i =tabel) = 1. 271
Jika dg IB, misalnya hanya perlu 4 pejantan Proporsi terseleksi = 4/4000 = 0.001 Intensitas seleksi ( i =tabel) = 3.37
Progres genetik :Hubungan Seleksi dengan nilai H
dan h
2Reproduksi
Pertumbuhan Karkas
1. h2 (heritabilitas) Jelek (0.0 – 0.15) Sedang (0,2 – 0.4) Tinggi (0.5 – 0.70) Progres genetik (seleksi)Rendah Sedang Tinggi
2. H (efek heterosis) Tinggi ( 10 – 20 %) Sedang ( 5 – 8 %) 0 % Perbaikan genetik (persilangan) Tinggi Sedang 0 Catatan: 1. Progress genetik =h2 x DS 2. Respon seleksi = R = ih2DS
