Back to Linked Genes

1. Back to Linked Genes Linked genes tend to be inherited together During crossing over between homologous chromosomes -- genes close together may “cross - over” together So what ? Alfred Sturtevant -- after WW I -- mapping chromosomes assumed equal chance of crossing over at all points on a chromosome hypothesized the farther apart 2 genes are -- the higher the probability that a crossover event would occur between them. used data from many crosses to assign relative positions of genes onto chromosomes (GENE MAPPING)

2. Crossing Over

3. Alfred Sturtevant – recombination frequencies used to determine distances between genes on a chromosome Predicted the farther apart two genes were on a chromosome, the higher the probability that crossing over would occur between them and, subsequently, a higher recombination frequency would be observed

4. Linkage Map Assuming a chromosome is a linear sequence of genes, Sturtevant assigned each gene a position on the chromosome using recombination frequencies This genetic map (linkage map) portrays the sequence of genes along a chromosome, without giving the precise location of the genes

5. Pedigree Analysis If know about genes [where they are and what they do] Basic science -- mysteries of embryonic development & evolution Human health - high blood pressure / heart disease / allergies / diabetes / mental illness / cancer Problem To study inheritance patterns in Humans we can't control matings and induce specific mutations What can be done is to assemble a family PEDIGREE (family tree of disease) Pedigree Analysis important for genetic counseling Given pattern from Pedigree can tell how the trait is inherited -- recessive / dominant / X-linked

6. Hemophila a Classic Example Hemophilia ? X-linked recessive disorder characterized by the inability to properly form blood clots Hemophilia played an important role in Europe’s history, for it suddenly cropped up in the children of Great Britain’s Queen Victoria. It became known as the “Royal disease” because it spread to the royal families of Europe through Victoria’s descendants Hemophilia first appeared in Victoria’s family in her eighth child, Prince Leopold, Duke of Albany Fortunately, Leopold was the only one of Victoria’s sons who suffered from hemophilia Her other three sons, Edward, Alfred, and Arthur, were unaffected. Since the present royal family of England descended from Edward VII, the first son, it is free from hemophilia.

7. The “Royal disease”