Genetics Ch. 5: Linkage, Recombination, Gene Mapping

Genetic linkage

certain alleles don’t assort independently during meiosis and tend to travel together for vertical generations

Recombination

separation of alleles on the same chromosome

Crossing over

exchange of DNA between paired homologous chromosomes occurring during meiosis

Syntenic

genes located on the same chromosome

Parental type

visual representation (phenotype) of F2 generation that looks like original parents

Recombinant type

visual representation (phenotype) of F2 generation that looks like mix of parents

What does recombination explain

how genes that are physically linked on same chromosome are often transmitted together and show genetic linkage 

Recombination in meiosis

physical breaking and rejoining of homologous maternal/paternal chromosomes

Cohesin

connections between sister chromatids soon after chromosomes have replicated

Recombination frequency

different gene pairs exhibit different linkage frequencies because genes are arranged in a line along a chromosome. used as a gauge of the physical distance separating any 2 genes on the same chromosome. 

Centimorgan (cM)

measures recombination frequency where 1 cM = 1 map unit = 1%

Recombination frequency < 50%

indicates LINKAGE

Loci

specific locations on particular chromosomes

Two-point cross

establish relative gene positions

analyzes 2 genes

Three-point cross

provides more accurate mapping

simultaneous analysis of 3 markers provides accurate picture of 3 linked genes

Double crossover

a genetic recombination event where two different segments are exchanged between homologous chromosomes at two separate locations and accounts for discrepancy in distance between genes 

Chromosomal Interference

occurrence of one crossover reduces the likelihood that another crossover will occur nearby on the same chromosome; chromosomes not occurring independently 

Linkage groups

genes chained together by linkage relationships

Chi-squared test

measures how well observed results conform to predicted ones; if statistically significant 

p < 0.05

reject null hypothesis with 95% confidence level