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Genotypic value is not transferred from parent to offspring; genes are.

Genotypic value is not transferred from parent to offspring; genes are. Need a value that reflects the genes that an individual carries and passes on to it’s offspring. Breeding Value. Empirically : An individual’s value based on the mean deviation of its progeny

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Genotypic value is not transferred from parent to offspring; genes are.

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  1. Genotypic value is not transferred from parent to offspring; genes are. Need a value that reflects the genes that an individual carries and passes on to it’s offspring Breeding Value Empirically: An individual’s value based on the mean deviation of its progeny from the population mean. Theoretically: An individual’s value based on the sum of the average effects of the alleles/genes it carries.

  2. . a1 = pa + qd - [ a (p – q) + 2dpq ] population mean f (A1) f (A2) Average Effect of an Allele Type of Values and Freq Mean value Population Average gamete of gametes of genotypes mean effect of gene A1A1 A1A2 A2A2 a d -a A1 p q pa + qd -a(p-q) + 2dpq q[a+d(q-p)] A2 p q -qa + pd -a(p-q) + 2dpq -p[a+d(q-p)] average effect of An: an = mean deviation from the population mean of individuals that received An from one parent, if the other parent’s allele chosen randomly a1 = q [ a + d (q – p)] a2 = –p [ a + d (q – p)]

  3. When there are only two alleles at a locus Average effect of a gene substitution A1A1 A1A2 A2A2 +a d -a (a - d) (d + a) p(a - d) + q(d + a) a = a + d(q - p) a pa

  4. Average Effects Frequency q (A2 orTHa2) 0.00.30.50.7 1.0 : THa1 0 9.3 12.5 13.3 10 :THa2 -40 -21.7 -12.5 -5.7 0   4031 251910 d = -15; a = 25

  5. Theoretically: An individual’s value based on the sum of the average effects of the alleles/genes it carries. Genotype Breeding Value 2a1 = 2qa A1A1 A1A2 A2A2 a1 + a2 = (q - p)a 2a2 = -2pa

  6. Breeding Values - THa example A2 or Tha2 Pop MeanA1A1A1A2A2A2 q = 1.0 150 20 20 0 q = 0.7 158.7 26.6 15.2 -11.4 q = 0.5 167.5 25 0 -25 q = 0.3 178.7 18.6 -24.8 -43.4 q = 0.0 200 0 -80 -80

  7. Sum of average effects across loci = Breeding Value (A) A1A1 A1A2 A2A2 2a1 a1 + a2 2a2 B1B1 B1B2 B2B2 2a1 a1 + a2 2a2 + (breeding values) (breeding values) G = A + D = + Genotypic Value Additive effects of genes Dominance deviation

  8. breeding value deviations from population mean phenotypic value of individual genotypic value of individual genotypic value breeding value genotypic value dominance deviation G = A + D G = G1 + G2 + I12 two-locus: interaction Partitioning the phenotypic value P = G Pop Mean P = A1 + D1 + A2 + D2 + I12 d=3/4a, q = 1/4

  9. One locus, two alleles P = A + D One locus, two alleles + environmental variation P = A + D + E environmental deviation Environmental effects on phenotypes

  10. Amount of genetic variation in a population depends on # of genotypes, genotypic value, and gene frequencies. More variation Less variation 0.75 0.75 p = 0.5 p = 0.9 0.50 0.50 0.25 0.25 10 10 11 9 11 9 A1A1 A1A2 A2A2 A1A1 A1A2 A2A2 Mean Mean

  11. a = d = 0.07 V . VP = VA + VD + VI + VE f (A1) total phenotypic variance additive genetic variance dominance genetic variance interaction (epistatic) genetic variance environmental variance Components of phenotypic variation P = A + D + I + E Variance partitioning: VP = VG + VE • Phenotypic variation can be decomposed into additive genetic and other variation • Relative contributions of different sources depend on allele frequencies

  12. VA = 2pq[a + d (q - p)]2 VD = (2pqd)2 TH alpha Example q = 0.7 191.24 151.62 39.69 q = 0.3 443.31 403.62 39.69 Genotypic, VG Additive, VA Dominance, VD d = -15; a = 25 (178.7) (158.7)

  13. Different environmental effects across genotypes result in G x E interaction variance VP = VA + VD + VI + VE + VGxE genetic x environmental interaction variance Environment and genotype can interact VP = VA + VD + VI + VE

  14. Heritability h2 = VA/Vp Proportion of total phenotypic variance attributed to variation in breeding values. Expresses the extent to which genes are transmitted from parents to offspring

  15. Drosophila wing length heritability (narrow sense): parental average (P) VA VP h2 = offspring (O) h2 = bOP bOP Detecting the genetic component of phenotypic variation Resemblance between parents and offspring indicates degree to which a trait is inherited Fraction of variation in parents that is explained by variation in their genes (VA). • heritability can also be estimated with offspring–midparent regression

  16. Bill depth in the Ground Finch 1976 h2 = 0.9 1978

  17. Heritability is often measured in the lab; estimates are higher than would be expected in nature. Almost all characteristics in almost all species are genetically variable to some extent.

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