• 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 P1: Purple starchy corn (homozygous dominant) is

crossed with White and waxy (homozygous recessive)F1:Resulting offspring all Purple and starchy. This generation is allowed to self pollinateF2: 147 Purple starchy

65 Purple waxy 58 White starchy 133 white waxy

• Which organisms in the F2 generation are recombinants?

• What is the expected ratio of offspring in the F2 generation if the genes are NOT linked?

• What is the recombination frequency of these 2 genes?

• Are these genes linked?

• Which organisms in the F2 generation are recombinants? Purple/Waxy and white starchy

• What is the expected ratio of offspring in the F2 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—c 10% b—c 4% c—d20%

a—d 30% b—d 16%a—e 6% b—e 20%

• 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)