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

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

3. 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

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

5. 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)

6. 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.

7. 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.

8. 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.

9. Mention natural selection here!

10. 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

13. 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