Chapter 11.5

Impact of Crossing Over on Inheritance AP Biology Fall 2010

Linked Genes

 Linkage Groups: linked genes on specific chromosomes ◦ Which are genes on the same chromosome that stay together more often than others ◦ Fruit fly example page 178

Linked Genes

 Linkage can be disrupted by crossing over- the exchange of parts of homologous chromosomes

Linked Genes

  Certain alleles that are linked on the same chromosome tend to remain together during meiosis because they are positioned closer together on the chromosome This eventually led to the generalization that

the probability that a crossover will disrupt linkage of two genes is proportional to the distance that separates them

Linked Genes

Linked Genes

  The careful analysis of recombination patterns in experimental crosses has resulted in linkage mapping of gene locations Human gene linkages were identified by tracking phenotypes in families over generations ◦ Crossovers are not rare and in some cases one crossover must occur between each chromosome before meiosis can be properly completed

Page 178- Review

   If genes A and B are twice as far apart as genes C and D on a chromosome, then we can expect crossing over to disrupt the linkage between genes A and B more frequently than between the other two genes Two genes are very closely linked when the distance between them is small Their combinations of alleles nearly always end up in the same gamete