Morgan’s Experiment Sex-linked genes in Drosophila flies Supported chromosome theory of inheritance Specific gene on specific chromosome

Sex Determination Male vs. Female Humans vs. other organisms SRY gene on Y chromosome Sex-determining region of Y

New Terminology Wild type- phenotype for a character most commonly observed in natural populations Sex-linked genes Hemizygous- males only in relation to sex chromosomes Sex-linked: located on either sex chromosome. Very few genes on the Y chromosome

Barr Bodies! One X in females becomes inactivated early on in embryonic development (XIST gene) Barr body X-inactive specific transcript

Linked Genes Genes located near each other tend to be inherited together Ex. Wing presence and body color of flies Genetic recombination- production of offspring with combinations of traits different than parents Parental type Recombinant types (recombinants)

Recombination Frequency …or Linkage Ratio: the percentage of recombinant types, If greater than 50%, then the genes are not linked, If less than 50%, then linkage is observed.

Linkage Genes closely located on the same chromosome do not recombine, unless crossing over occurs The recombination frequency gives an estimate of the distance between the genes.

Recombination Frequencies Genes that are adjacent have a recombination frequency near 0%, Genes that are very far apart on a chromosome have a recombination frequency of 50%, The relative distance between linked genes influences the amount of recombination observed.

Mention natural selection here!

Genetic Map Ordered list of genetic loci on a chromosome Linkage map is one based on recombination frequencies Map unit= 1% recombination frequency NO precise location on chromosome

Simple Mapping white eyes x miniature = 36.9 mu, white eyes x yellow body = 0.5 mu, miniature x yellow body = 38 mu, w 0.5 mu 36.9 mu m y 38 mu