AnSci 361 1st Edition Lecture 9 Outline of Last Lecture I. Double Musclinga. MethodsOutline of Current Lecture I. Physiological evaluation of DMII. Genetics of double musclinga. Myostatini. Mapping geneii. Identifying geneb. Homozygosity mappingIII. Arthrogryposisa. Geneticsb. GAR PrecisionIV. DNA testinga. ApplicationCurrent LecturePhysiological evaluation of DM:• High number of muscle fibers• DM cattle contains less connective tissues (increases tenderness?)• During forced exercise, DM cattle shows signs of fatigue faster than normal cattle (reduced blood circulation)• Less marbling (intramuscular fat)• Reduced fertility; high embryo mortality rate• High proportion of lean meat and low fat makes it healthy? Genetics of Double Muscling:These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.• Myostatin (MSTN) gene maps to Chr. 2• Three exons and two introns in all species studied: pig, chicken, zebra fish, mouse• Myostatin represses skeletal muscle growth• Mutations lead to muscle hypertrophy • Six mutations: deletions, insertions, point mutationsHow was the gene mapped? Positional candidate gene approach:- Belgian Blue: fixed for the muscular hypertrophy (mh) allele - Friesian cattle: fixed for the wild type allele - Genotyping with molecular markersMapping the Myostatin gene using a backcross design:• Belgian Blue fixed for muscular hypertrophy • Friesian fixed for wild type allele• Normal or double muscled backcross offspring • Genotyping with microsatellites• Gene mapped on Chr. 2• QTL mapping • Test association between marker allele inheritance and phenotypeA major challenge: Identify the actual gene!- Comparative mapping approach- Bovine Chr. 2 region corresponds to myostatin region in mice- Knockout mouse gene: extreme muscle developmentHomozygosity mapping:- The phenotype is rare or lethal- Mode of inheritance: recessive- Affected individuals are homozygous- Then, the traits can be mapped using a relatively small number of individuals with common ancestorWhat is Arthrogryposis Multiplex (AM)?- Is it genetic? Mode of inheritance?- Development of a DNA test and applicationo Curly calf syndrome- Emerged in Angus cattle in 2008 in Australia and the USA- Disease derives its name from Greek, literally meaning 'curved or hooked joints'- Arthrogryposis: the permanent fixation of a joint in a contracted positiono Can include muscle weakness and fibrosis- Small size and thin appearanceo Bent or twisted spine- Affected calves are full term; die shortly before or during birtho Reduced birth weight (15-25 kg)Is it genetic? Mode of inheritance?- Do affected individuals have common ancestors?- Does it appear in specific families?- Do disease status and relationship suggest a mode of inheritance?Common ancestor GAR Precision 1680:- Appeared in both paternal and maternal sides of pedigreeMapping and Development of DNA test:• Genotype affected individuals with high density (54,000 SNPs) SNP chip• find a region of the genome where all affected individuals are homozygous• Homozygosity mapping• Assumption of analysis: phenotype due to homozygosity for recessive alleleMapping results: Dr. Beever found a deletion:• Affected animals have two copies of a chromosome with a section missing (deletion)• Deletion spans an area containing two genes (one critical for normal fetal development)• DNA test for AM developed (4 months after start of project)• Tested 736 Angus AI sires: • Found 62 carriers • none with affected genotype as expectedApplication:• Since 2008, tens of thousands of Angus cattle tested• Thousands of AM carriers have been culled• Select non-carrier offspring from carrier parents• Little concern if