Transcript Chapter 11.5

Chapter 11.5
Impact of Crossing Over on Inheritance
AP Biology
Fall 2010
Linked Genes
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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
