Genome mapping

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Genome mapping

  1. 1. LINKAGE ANALYSIS IN GENETIC MAPPING
  2. 2. WHAT IS A GENOME? • It is the entirety of an organism's hereditary information • It is encoded either in DNA or, for many types of viruses, in RNA
  3. 3. GENOME MAPPING It is the creation of a genetic map assigning DNA fragments to chromosomes A genome map provides a guide for the sequencing experiments by showing the positions of genes and other distinctive features DNA sequencing has some major limitation – only 750 bp can be examined in a single experiment
  4. 4. Two Types Of Genome Mapping 1. Genetic Mapping 2. Physical Mapping
  5. 5. •It is based on use of genetic techniques to construct maps showing the positions of genes and other sequence features on a genome. •It includes cross breeding experiments or examining the family histories in case of humans GENETIC MAPPING
  6. 6. MARKERS Various types of markers were used in mapping the genome 1. Genes were the 1st markers used 2. DNA markers RFLPs (Restriction fragment length polymorphisms) SSLPs (Single sequence length polymorphisms) SNPs (Single nucleotide polymorphisms)
  7. 7.  After obtaining a set of markers to construct a map, mapping techniques came in the role.  This techniques are based on genetic linkage  Genetic mapping is based on inheritance  Mendel from his breeding experiments with pea plant concluded that pea plant possesses two alleles for each gene, but displays only one genotype  He therefore described it as dominant or recessive phenotype  But Mendel did not encounter the other complications like incomplete and co dominance while performing this experiments Linkage Analysis Is The Basis Of Genetic Mapping
  8. 8. Incomplete Dominance • The heterozygous phenotype is somewhere between the two homozygous phenotypes • Case in which one allele is not dominant over another Red flower (RR) White flower (WW)Pink flower (RW)
  9. 9. Co dominance • Both alleles contribute to the phenotype
  10. 10. Apart from dominance recessiveness Mendel carried out additional experiments by which he established his two laws Laws Of Genetics :- 1. Alleles segregate randomly 2. Pairs of alleles segregate independently
  11. 11. Inheritance of the alleles of gene T is independent of inheritance of the alleles of gene B
  12. 12. Partial Linkage  Genes reside on chromosome  Chromosomes are inherited as intact units, so it was reasoned that the alleles of some pairs of genes will be inherited together because they are on the same chromosome  Pairs of genes were either inherited independently, as expected for genes in different chromosomes, or, if they showed linkage, then it was only partial linkage sometimes they were inherited together and sometimes they were not
  13. 13. Recombination Frequency Arthur Sturtevant’s, an undergraduate in Morgan laboratory • The frequency with which the genes are unlinked by crossovers will be directly proportional to how far apart they are on their chromosome • The recombination frequency is therefore a measure of the distance between two genes • If you work out the recombination frequencies for different pairs of genes, you can construct a map of their relative positions on the chromosome • Recombination frequency can be calculated by LOD score method
  14. 14. LOD score • The LOD score is calculated as follows: • LOD = Z = Log10 probability of birth sequence with a given linkage probability of birth sequence with no linkage • By convention, a LOD score greater than 3.0 is considered evidence for linkage. • On the other hand, a LOD score less than -2.0 is considered evidence to exclude linkage.

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