Ansc 305 1st EditionExam # 2 Study Guide I. FormatA. 5 questionsi. Calculate average weaning weights predicted crossbred performance equationii. Discuss birth weights in Bos indicus and Bos Taurus cattle and their crossesiii. Horse color inheritance questionsiv. Discuss hybrid vigor, breed differences, horse color traits, etcv. Construct a relationship covariance chartII. Predicted crossbred performanceA. Equationi. Pcross= weighted breed average + correction for maternal breed differences + direct hybrid vigor (in the offspring) + maternal hybrid vigor (in the dam)ii. Correction for maternal breed differences is the sum of the fraction of the breedof concern in the dam minus the amount of that breed in the offspring times thematernal effect (M value) of that breed (where the summation is across all breeds in the offspring)iii. Direct hybrid vigor is the sum of the fraction of loci in the offspring expected to carry one allele from one breed and the other allele from the other breed times the direct hybrid vigor between these two breeds (where the summation is across all pairs of breeds in the offspring). iv. If the sire has the proportion a1 of breed A and the proportion of b1 of breed B and the dam has corresponding proportions of a2 and b2, then the fraction of loci in the offspring expected to carry one allele from one breed and the other allele from the other breed is equal to (a1 X b2) + (b1 X a2)v. Weighted breed average is simply the average of the parental breeds weighted by their proportions in the offspring. If the animal is half Hereford and half Angus then ½(490) + ½(500) = 495. vi. Maternal hybrid vigor is the sum of the fraction of loci in the dam expected to carry one allele from one breed and the other allele from the other breed times the maternal hybrid vigor between these two breeds. Use (a1 X b2) + (b1 X a2). Same thing as the direct hybrid vigor except you are using it for the dam, you areusing the dam’s parents in the calculation.III. Bos indicus vs. Bos TaurusA. Birth weightsi. Bos indicus (like Brahman) sired calves out of Bos taurus (like Hereford) cows have much heavier average birth weights than Bos taurus sired calves out of Bos indicus cows (15-20 lbs heavier)ii. In Bos indicus sired calves out of Bos taurus cows, the bull calves are much heavier (12-16 lbs) than the heifer calves. In Bos taurus sired calves out of Bos indicus cows, there is little difference in average birth weight between bull and heifer calves. In straight Bos indicus and Bos taurus calves, the bull calves are about five pounds heavier than the heifer calves.iii. For various crosses, the more Bos indicus in the sire compared to the amount of Bos indicus in the dam, the heavier the calves tend to be and the larger the difference between the bull and heifer calves tends to be.iv. When embryos of the above four types are transferred to cows of a given type (Holstein, for example), the same types of differences between crosses and between sexes within crosses are found. Whatever is responsible for these differences has already occurred by the seventh day of pregnancy. (It may have happened at conception).v. If the sire and dam have the same amount of Bos indicus in them, there is about a 5 lb difference in bull and heifer calves (bulls are heavier).IV. Horse Color InheritanceA. Extension locus (E and e alleles)i. Differences in genotype at this locus result in bay or black vs sorrel or other chesnut base colors. Linked to the roaning, tobiano and sabino- 1 loci. ii. E and T are 10 cM apart—crossover 10% of the timeB. Restriction (or agouti) locus (A and a alleles)i. Differences in genotype at this locus result in bay vs black base colors (in horses that have the EE or Ee genotypes). Restricting black color to points.C. Roaning locus (R and r alleles) i. Heterozygotes are roan. Homozygotes for the roaning allele (R) has been thought to cause an early embryonic lethality; however, several horses have been identified that breed as if they are homozygous RR; these homozygous roans do not differ phenotypically from heterozygotes. Linked to extension, tobiano, and sabino-1 loci.D. Graying locus (G and g alleles)i. Epistatic to everything elseii. Presence of the G allele causes progressive graying of the base coloriii. Homozygotes grey out fasterE. Non- lineback dilution locus (C and c alleles)i. Presence of the c allele (in heterozygotes) causes dilution of bay to buckskin and sorrel to palomino; some, but not all, blacks are diluted to smokey. Homozygotesare cream colored.F. Lineback dilution locus (D and d alleles) i. Presence of the D allele causes dilution of bay to dun, black to grullo, and sorrel to red dun.G. Dominant white locus (W and w alleles)i. Presence of the W allele causes white color in some heterozygotes and a sabino pattern in others. Homozygous condition is lethal (early embryonic lethality).H. Tobiano locus (T and t alleles)i. Presence of the T allele causes the tobiano paint pattern. Linked to the extension, roaning, and sabino-1 loci. I. Frame locus (F and f alleles) i. Heterozygotes have the frame overo pattern. Homozygosity of the frame allele (F) results in the lethal white foal syndrome. J. Sabino locus (Sb- 1 and sb-1 alleles)i. Presence of the Sb-1 allele causes the sabino overo pattern. Linked to the extension, roaning, and tobiano loci. Homozygotes are nearly solid white. K. Splashed white pattern (Spl and spl alleles)i. Presence of the Spl allele causes the splashed white overo pattern. Many splashed white horses are deaf. Homozygotes, apparently, are solid white. L. Appaloosa Complex (Ap and ap alleles)i. Presence of the Ap allele causes one of the Appaloosa patternsii. Heterozygotes vary from minimally to maximally white and most have leopard spots; homozygotes also vary from minimally to maximally white, but almost entirely without leopard spots, resulting in snow cap blankets or few spot leopards. iii. Homozygotes are night blind. M. Pattern Locus (Pn and pn alleles) i. Presence of the Pn allele causes the leopard pattern if the Ap allele is present V. 5 Categories of Commercial Breeding SystemsA. Commercial Straightbreedingi. Example: 4 Angus bulls bred to 100 Angus females. Keep 40% of the heifer calvesfor replacement and sell the rest of the heifer calves and all of the steer calves.ii. Advantages: 1. Production of a “specialty” product (milk, finewool, CAB- certified angus beef) 2. Simplicity of management3. Possibility of family