Chapter 11.5

1. Chapter 11.5 Impact of Crossing Over on Inheritance AP Biology Fall 2010

2. 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

3. Linked Genes • Linkage can be disrupted by crossing over- the exchange of parts of homologous chromosomes

4. 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

5. Linked Genes

6. 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

7. 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