PARAMETER GENETIK: Pengantar heritabilitas dan ripitabilitas

Transkripsi

1 PARAMETER GENETIK: Pengantar heritabilitas dan ripitabilitas Pendahuluan: Timbulnya keragaman berbagai sifat kuantitatif Derajat keragaman yang dihitung ( Rataan, varians dan SD) BERAPA BAGIAN DARI PERBEDAAN DIANTARA INDIIDU AKAN DAPAT DIWARISKAN Sifat Kuantitatif: Aksi sejumlah besar gen (POLOGEN) Setiap gen mempunyai aksi berbeda ( A, D, E) aditif, dominan,epistasi Performans (P) = Faktor-faktor (G + E) ar P = ar G + ar E ar G = penting, karena inilah yang akan diwariskan orang tua kepada keturunannnya.

2 Parameter Genetik Umum : 1.Heritabilitas ( h2) 2.Ripitabilitas ( r) : L1, L2, L3, L4 Manfaat Utama dalam Genetika/Pemuliaan: Nilai Pemuliaan (NP) MPPA

3 Heritabilitas 1. Heritability in the broad sense (H 2 ): is the proportion of the phenotypic variance that is due to genetic effects including additive, dominance and epistasis: H 2 G P A 2. Heritability in the narrow sense (h 2 ): is the proportion of the phenotypic variance that is due to additive genetic effects only. D P I h 2 A P = A A D I EP ET 3

4 Heritabilitas: Pengertian Umum: 1. Berapa bagian dari var P total yang berasal dari pengaruh gen gen aditit h 2 = var A/ var P 2. Berapa bagian dari var individu dalam kelompok tetua terseleksi dapat diwariskan kepada keturunannya 3. Berapa besar ketepatan fenotipik untuk menduga nilai genetik 4. Regresi antara nilai genetik dan nilai fenotip

5 Heritability is always positive ranging from 0 to 1.0. Traits with low heritability (h 2 < 0.20): reproductive traits like days open calving interval, litter size, and conception rate longevity or productive live ( about 0.10) weaning weight in swine ( about 0.10) Moderately heritable traits (h 2 of 0.2 to 0.4): Milk yield, fat yield and protein yield ( ) Birth weight in sheep Yearling weight in sheep Highly heritable traits (h 2 > 0.4): Carcass traits and traits related to skeletal dimensions like mature body weight Fat and protein% in milk. 5

6 Manfaat Nilai Heritabilitas 1. Menduga nilai pemuliaan (NP) NP = h2 ( Pi Pp) Pi performans individu Pp rataan performans kelompok 2. Mengetahui besarnya nilai Respon seleksi R = h 2. DS = h2 ( Xs Xp) Xs = rataan fenotip setelahh seleksi Xp = rataan fenotip populasi 3. Sebagai dasar pengembangan sebagian besar teori (model) penerapan pemuliaan ternak.

7 Contoh (penggunaan h2) Berat sapih (BS) sapi potong populasi : kg (kisaran kg) Diseleksi (rataan seleksi) : 125 kg Heritabilitas BS = Estimasi BS pada generasi N + 1???? 1. Untuk Seleksi: Pada GENERASI (N+ 1) Differensial seleksi : ( rataan terseleksi rataan populasi) ( ) = 5 kg Respon seleksi : heritabilitas x diferential seleksi 0.48 x 5 = 2.4 kg Estimasi Berat Sapih pada Generasi N + 1= = = kg 2. Menghitung Nilai Pemuliaan (breeding value): mis ada Individu Misalnya BS : 125 kg NP = h2 (Pi-Pp) = 0.48 ( ) = 0.48 x 5 = 2.5 kg

8 RIPITABILITAS Repeatability (r) is the proportion of the phenotypic variance that is due to permanent effects (genetic effects and permanent environmental effects): r A D P I What does the repeatability measure? EP 1. The strength of the relationship between repeated records. Therefore, repeatability can be estimated as the correlation between repeated records on the same animals. 2. The strength of the relationship between single performance records and producing ability (permanent effects).. 8

9 Manfaat Ripitabilitas 1. It is useful in prediction of producing ability and therefore the animal s next record from the current and previous records: - If r is high, we can predict the animal s next record more accurately - If r is low then the prediction of the next record has low accuracy. 2. Repeatability is important in prediction of breeding values (Nilai Pemuliaan) from multiple records on the same animals: Bˆ i 2 nh 1 ( n 1) r ( P i P) 9

10 3. Repeatability is important in making culling decisions ( dalam program seleksi) When r is high we can cull animals of poor performance on the basis of the first record When r is low one should wait for more records before making a culling decision on the animal. Examples of Repeatability Estimates Beef cattle: - Calving date (trait of the dam): Birth weight (trait of the dam): Weaning weight (trait of the dam): Body measurements: 0.80 Dairy cattle: - Services per conception: Calving interval: Milk yield: % Fat: Teat placement: 0.55 Poultry: - Egg weight: Egg shape: Shell thickness: 0.65 Sheep: - Number born: Birth weight (trait of the dam): day weaning weight (trait of the dam): Fleece grade:

11 Contoh penggunaan r ; MPPA (PA) Example: suppose a cow has three milk records: 4000kg in the first record, 5000 kg in the second, and 6000 kg in the third. Suppose also that the mean of all cows is 4600 kg and the repeatability of milk yield is 0.60, then the predicted producing ability of this cow is: PAˆ (3)(0.60) i ( ) 327kg 1 (3 1)(0.60) Pˆ i P PAˆ kg 11