Genes A B and C are linked on a chromosome and found in the

Genes A, B, and C are linked on a chromosome and found in the order A-B-C. Genes A and B recombine with a frequency of 7%, and genes B and C recombine at a frequency of 25%. For the cross:

a + b + c/abc + × abc/abc,

predict the frequency of progeny. Assume interference is zero.

a) Predict the frequency of a⁺b⁺c progeny _________

Please show work so I can learn to do this. Thank you!

Solution

Answer:

a+---7----b+------------25--------------c+

a-----------b--------------------------------c

a+ bc & ab+c+ gametes are produced in 7% (each 3.5%)due to cross over between gene a & b.

a+b+ c & abc+ gametes are produced in 25% (each 12.5%) due to cross over between gene b & c.

Double cross over recombination frequency = (RF b/w first and second loci) RF b/w second and third loci)

= (7/100) (25/100) *100

= 0.07 * 0.25 * 100 = 1.75

a+bc+ & ab+c gametes are produced in 1.75% (each 0.875%) due to dobule cross over at a time.

Total recombinants = 7 + 25+ 1.75= 33.75

Non recombinants = 100-33.75= 66.25%

The frequency of progeny as follows

a+ bc/abc---3.5%

ab+c+/abc---3.5%

a+b+c/abc ----12.5%

abc+/abc-----12.5%

a+bc+/abc----0.875%

ab+c/abc----0.875%

a+b+c+---33.125%

abc/abc----33.125%