Recombinants (formed by recombination) – Offspring with a new combination of characteristics different from their parent Recombinants of Linked genes – In order for recombination of linked genes to occur, the genes must be “separated” by crossing over – The closer genes are located to one another the less likely crossing over will “separate” them
Calculating recombination frequency – Add the total number of recombinants in each class – Divided by the total number of offspring produced – Multiply by 100 (to get a %) – Map units = recombination frequency
Example – Zea Mays P 1 :Purple starchy corn (homozygous dominant) is crossed with White and waxy (homozygous recessive) F 1 :Resulting offspring all Purple and starchy. This generation is allowed to self pollinate F 2 : 147 Purple starchy 65 Purple waxy 58 White starchy 133 white waxy
Which organisms in the F 2 generation are recombinants? What is the expected ratio of offspring in the F 2 generation if the genes are NOT linked? What is the recombination frequency of these 2 genes? Are these genes linked?
Which organisms in the F 2 generation are recombinants? Purple/Waxy and white starchy What is the expected ratio of offspring in the F 2 generation if the genes are NOT linked? 9:3:3:1 What is the recombination frequency of these 2 genes? 123/403 = 31% Are these genes linked? Yes, recombination frequency is less than 50%
Gene Map Recombination frequency = map units EX. The following recombination frequencies were found. Determine the order of these genes on the chromosome. a—c10%b—c4%c—d20% a—d30% b—d16% a—e6%b—e20%
Answer: E A C B D 30%= 30 units (a-d) 6 (a-e) 10 (a-c) 4 (b-c)16 (b-d) 20 (b-e) 20 (c-d)