Morgans Experiment Sexlinked genes in Drosophila flies Supported

Morgan’s Experiment �Sex-linked genes in Drosophila flies �Supported chromosome theory of inheritance

Sex Determination �Male vs. Female �Humans vs. other organisms �SRY gene on Y chromosome

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

Barr Bodies! �One X in females becomes inactivated early on in embryonic development (XIST gene) �Barr body

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.

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, 0. 5 mu 36. 9 mu y w m 38 mu