1. Gene mapping
March 3, 2017

2. Background
Gene is a locus (or region) of DNA which is made up of nucleotides and is the molecular unit of heredity
Nucleotides any of a group of molecules that, when linked together, form the building blocks of DNA or RNA
Heredity the passing on of physical or mental characteristics genetically from one generation to another

4. Chromatid vs Chromosome
Half of a chromosome is called a chromatid, but when meiosis is taking place we call each of the chromatids a chromosome because chromosomes are counted by their centromeres…

5. Recombination
Genetic recombination is the production of offspring with combinations of traits that differ from those found in either parent

6. Recombination
Linked genes are generally found on the same chromosome and are hence usually inherited (or handed down) together
Locus where genes are found on a chromosome
Centimorgan (abbreviated cM) or map unit (m.u.) is a unit for measuring genetic linkage. It is defined as the distance between chromosome positions

7. Frequency of recombination
Frequency of recombination is a measure of the degree to which recombinant types are found following crosses (matings) between specific parental types and is a measure of the likelihood of crossing over events occurring between the two genetic loci being considered during these test crossings
If the two loci are not linked then the frequency of recombination will be equal to 50%
If the two loci are linked then the frequency of recombination will be less than 50%
Frequency of Recombination = recombination types / Total (recombination types + parental types)

8. Frequency of Recombination= 7/20 Frequency of Recombination= .35
Phenotype
# of organisms for each type
Parental 5 8
Recombinant 3 4
Frequency of Recombination = recombination types / Total (recombination types + parental types)
Frequency of Recombination= 7/20
Frequency of Recombination= .35
35% Frequency of recombination meaning the loci are linked(same chromosome)

9. Gene Mapping
We use the frequency of recombination to determine the distance between genes.

10. Frequency of Recombination
Gene mapping Example
Gene
Frequency of Recombination
A-B
17%
A-C 8%
C-B 9% C A C B C

11. FREQUENCY OF RECOMBINATION
GENE
FREQUENCY OF RECOMBINATION
A-B 30
B-C 45
B-D 40
A-D 25 B A D C