3. Genetic Mapping The proportion of recombinants resulting from a dihybrid test cross is used to calculate the cross over value (COV), a measure of linkage, and if linkage occurs, the distance between genes . COV is also known as recombination frequency.

7. Cross over (meiosis) Homologous chromosome in synapsis – 4 chromatid (tetrad) P Q p q kiasma r R

8. Genetic mapping of Drosophila melanogaster genes

9. Example P : CCSS x ccss P : CS/CS x cs/cs G : CS cs F1 : CS/cs x cs/cs G : CS cs Cs cS cs x co co CS/cs cs/cs cS/cs Cs/cs 480 480 20 20 Parent combination Recombinant

10. Genotype Individuals CS/cs 480 cs/cs 480 Cs/cs 20 cS/cs 20 Parent combination Recombinant (cross over) Eg : Test cross F1 : CS/cs x cs/cs Parent combination = (480 + 480)/1000 = 96% Recombinant = (20 + 20)/1000 = 4% (cov) If C/c dan S/s genes is far apart, cov > 4% Jumlah 1000 C S 4 map unit

12. Solution : R and Q= 40% P and Q = 35% R and S = 30% Q and S = 10% P and R = 5% R Q 40 map unit 5 25 10 S P

13. Cross over value given for P and Q = 4% P and R = 1% State the cross over value possible for Q and R. P Q 4 1 3 Cross over value for Q and R = 3% P Q 4 1 Cross over value for Q and R = 5% EXERCISE 2 R R

18. I II III Circle = female Square = male Roman = generation Numbers = individuals in generation Colored = different phenotype 1 2 1 1 2 4 3

19. Eg: “widow’s peak” trait (dominant allele) W Allele = widow’s peak w allele – no widow’s peak

20. I II III Widow’s peak pedigree Color = widow’s peak Ww ww ww WW @ Ww ww Ww Ww