You conduct a trihbybrid cross starting with a parental generation consisting of

ID: 78953 • Letter: Y

Question

You conduct a trihbybrid cross starting with a parental generation consisting of a female expressing the mutant condition for all three traits and a male that is wild type for all three traits. This cross produces 1000 F2 offspring. The following are phenotypes among the F2 offspring.

161

1)Which of the three genes for these traits lies in between the other two?

2) What is the recombination frequency estimated from these data for the whiskers and spotted belly traits?

3) What is the recombination frequency estimated from these data for the whiskers and green eyes traits?

4)What is the chromosome interference value estimated from these data for this region of the chromosome?

Whisker trait spotted belly trait green eye trait # F2 offspring + + + 320 Whiskers Spotted Belly Green eyes 335 + Spotted belly +

161

Whiskers + Green eyes 158 Whiskers Spotted belly + 12 + + Greeny eyes 9 Whiskers + + 3 + Spotted belly Greeny eyes 2

Explanation / Answer

Answer:

1) The three genes for these traits lies in between the other two is whisker gene.

2). The recombination frequency estimated from these data for the whiskers and spotted belly traits = 32.4% = 0.324

3). The recombination frequency estimated from these data for the whiskers and green eyes traits = 2.6% = 0.026

4). Interference = 1-CC = 1-0.625 = 0.375

Explanation:

Whisker = w

Spotted belly= s

Green eye = g

Shorthand

Number of progeny

w s g

320

+ + +

335

+ s +

161

w + g

158

w s +

+ + g

w + +

+ s g

Usually parental combinations will be more than the recombinants, so the arrangement of genes in heterozygous condition is + + + / w s g

1. If single cross over (SCO) occurs between w & s

Normal order= w---------s & +-----+

After cross over= w-----+ & +------s

w-----+ recombinants are 158 + 3 = 161

+------s recombinants are 161 + 2 = 163

Total recombinants = 324

RF = (324/1000.)*100 =32.4%

2. If single cross over (SCO) occurs between s & g

Normal order= s---------g & +----+

After cross over= s-----+ & +------g

s-----+ recombinants are 161+12=173

+------g recombinants are 158 + 9 = 167

Total recombinants = 340

RF = (340 / 1000)*100 = 34%

3. If single cross over (SCO) occurs between w & g

Normal order= w---------g & +------+

After cross over= w-----+ & +------g

w-----+ recombinants are 12+3 = 15

+------g recombinants are 9 + 2 = 11

Total recombinants = 26

RF = (26/1000)*100 =2.6%

% RF = Map unit distance

The order of genes is -----

s-----------32.4 m.u.-----------w-- 2.6m.u.--g

1) The three genes for these traits lies in between the other two is whisker gene.

2). The recombination frequency estimated from these data for the whiskers and spotted belly traits = 32.4% = 0.324

3). The recombination frequency estimated from these data for the whiskers and green eyes traits = 2.6% = 0.026

Expected double cross overs = 0.324 * 0.026 = 0.008

Observed double cross overs = 3 + 2 = 5

Observed double cross over frequency = 5/1000 = 0.005

Observed double cross progeny are more than the expected double cross over progeny.

Coefficent of coincidence (CC) = Obeserved dco / Expected dco

CC = 0.005/0.008 = 0.625