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Theoretical Expected Genetic Gains for Among-and-Within-Family Selection Methods in Perennial Forage Crops

^a USDA-ARS, U.S. Dairy Forage Research Center, Madison, WI 53706-1108
^b Center for Applied Genetic Technologies, Crop and Soil Science Dep., Univ. of Georgia, 111 Riverbend Rd., Athens, GA 30602

View larger version (33K): [in this window] [in a new window]   Figure 1. Schematic flow diagram of four family-selection methods differing in recombination unit, assuming 2 yr of data collection before selecting the best families. Each selection method begins with the development of N half-sib families (HSF) or full-sib families (FSF), which are planted in field trials for phenotypic measurement of trait Y. Half-sib family (HSF) and full-sib family (FSF) selection utilize n = 1/p random plants from f = Np selected families as the recombination unit, where p = proportion of families selected. Among-and-within family selection utilizes plants selected from the best families for trait Y (AWF-HS and AWF-FS) or plants selected for an alternative trait (X) within families (AWFX-HS and AWFX-FS). Half-sib progeny test (HSPT) and full-sib progeny test (FSPT) selection methods use saved parental clones as the recombination unit, requiring establishment of an additional recombination nursery to increase the number of families back up to N for continuation of the next selection cycle.

View larger version (28K): [in this window] [in a new window]   Figure 2. Expected gains from half-sib progeny-test (HSPT) selection (two solid lines, one for a 5-yr cycle time and one for a 7-yr cycle time) and among-and-within-family (AWF-HS) selection for six different within-family selection intensities (p2) (dashed lines, all for a 5-yr cycle time), expressed as a function of the within-family (individual-plant) heritability. All expected gains for HSPT and AWF-HS selection are expressed as a percentage of gains for half-sib family (HSF) selection. Within-family heritability (x axis) is expressed as a proportion of the among-family heritability, 0.20).

View larger version (27K): [in this window] [in a new window]   Figure 3. Expected gains from full-sib progeny-test (FSPT) selection (two solid lines, one for a 5-yr cycle time and one for a 7-yr cycle time) and among-and-within-family (AWF-FS) selection for six different within-family selection intensities (p2) (dashed lines, all for a 5-yr cycle time), expressed as a function of the within-family (individual-plant) heritability. All expected gains for FSPT and AWF-FS selection are expressed as a percentage of gains for full-sib family (FSF) selection. Within-family heritability (x axis) is expressed as a proportion of the among-family heritability, 0.20).

View larger version (35K): [in this window] [in a new window]   Figure 4. Expected gains from half-sib progeny-test (HSPT) selection (two solid lines, one for a 5-yr cycle time and one for a 7-yr cycle time) and among-and-within-family (AWFX-HS) selection for two traits (Y among families, X within families) for 11 different within-family selection intensities (p2) (dashed lines, all for a 5-yr cycle time), expressed as a function of rghX, the product of the genetic correlation between X and Y (rg) and the square root of individual-plant heritability for X (hX). All expected gains for HSPT and AWFX-HS selection are expressed as a percentage of gains for half-sib family (HSF) selection.

View larger version (33K): [in this window] [in a new window]   Figure 5. Expected gains from half-sib progeny-test (FSPT) selection (two solid lines, one for a 5-yr cycle time and one for a 7-yr cycle time) and among-and-within-family (AWFX-FS) selection for two traits (Y among families, X within families) for 11 different within-family selection intensities (p2) (dashed lines, all for a 5-yr cycle time), expressed as a function of rghX, the product of the genetic correlation between X and Y (rg) and the square root of individual-plant heritability for X (hX). All expected gains for FSPT and AWFX-FS selection are expressed as a percentage of gains for half-sib family (FSF) selection.