Gene Mapping - Lecture 13 Flashcards
What are gene maps?
○ The relative order of genes on the chromosome
○ The distance between the genes
Why are gene maps useful?
○ Identify genes linked to diseases or traits
○ Aid in studying gene function
○ Support animal/breeding programs
○ Compare genome structures across species
What are the three types of maps?
○ Genetic/linkage map: based on crossover events between different genes
○ Cytogenetic map: Based on bonding
○ Physical map: based on DNA sequence of the gene itself
How was the first physical map made and what does it show?
○ Made using restriction enzymes that cut DNA at specific sites
○ Green bar = gene
○ Red bar = exons
○ Spaces between genes = intergenic region
How are human cytogenic maps made and what do they show?
○ Made by staining with giesma which gives the appearance of light and dark bands on the chromosomes
○ Gives a visual representation of an entire set of chromosomes
How are genes named?
○ Genes are assigned to the short p or long q arm
○ Then to a region, then to a band, then to a sub-band
What the principles of linkage mapping?
○ Crossing-over occurs at random positions along each chromosome
○ The frequency of recombinant gametes is proportional to the frequency of crossing-over and distance apart on the same chromosome
What does recombination frequencies tell us?
50% recombinant gametes:
○ Genes on different chromosomes
○ Far apart on the same chromosomes
Less than 50% recombinant gametes:
○ Genes are linked on same chromosome
○ The smaller the RF, the closer the genes
Why aren’t genetic distances exactly additive?
○ Over large genetic distances double crossover events underestimate the true distance
○ Crossover events are not always independent
○ Frequency of crossing over varies in different regions of the genome e.g. higher in subtelomeric regions
