Questions 16-20. You have crossed a corn with small leaves (sm) and short stems

ID: 80476 • Letter: Q

Question

Questions 16-20. You have crossed a corn with small leaves (sm) and short stems (st) to a corn with yellow kernels (ye). The F1 generation were all completely wild type. You then crossed the F1s to corn with small leaves, short stems and yellow kernels. The 1000 F2 progeny looked as follows: 336 small leaves, short stems 334 yellow kernels 91 small leaves, yellow kernels 89 short stems 64 small leaves, 66 short stems, yellow kernels 11 wild type 9 small leaves, short stems, yellow kernels Which gene is in the middle? a. sm b. St c. ye d. the genes are unlinked e. the genes are too tightly linked to determine What is the distance between sm and st? a. 10 map units b. 15 map units c. 20 map units d. 31 map units e. 35 map units 18. What is the distance between sm and ye? a. 10 map units b. 15 map units c. 20 map units d. 31 map units e. 35 map units What is the distance between st and ye? a. 10 map units b. 15 map units c. 20 map units d. 31 map units e. 35 map units

Explanation / Answer

Answer:

16). c. ye

17). d. 31 map units

18). c. 20 map units

19). a. 10 map units

Explanation:

Phenotype

Shorthand

Number

Small leaves, short stems

sl st +

336

Yellow kernels

+ + y

334

Small leaves, Yellow kernels

sl + y

Short stems

+ st +

Small leaves

sl + +

Short stems, yellow kernels

+ st y

Wild

+ + +

Small leaves, short stems, Yellow kernels

sl st y

Usually parental combinations will be more than the recombinants, so the arrangement of genes in heterozygous condition is sm st + / + + ye

1. If single cross over (SCO) occurs between sm & st and + & +

Normal order= sm---------st & +-----+

After cross over sm-----+ & +------st

sm-----+ recombinants are 91+64 = 155

+------st recombinants are 89+66 = 155

Total recombinants = 310

RF = (310/1000.)*100 =31 %

2. If single cross over (SCO) occurs between st & + and + & ye

Normal order= st---------+ & +----ye

After cross over= st-----ye & +------+

st-----ye recombinants are 66+9 = 75

+------+ recombinants are 64+11=75

Total recombinants = 150

RF = (150 / 1000)*100 = 15%

3. If single cross over (SCO) occurs between sm & + and + & ye

Normal order= sm---------+ & +------y

After cross over= sm-----ye & +------+

sm-----ye recombinants are 91+9 = 100

+------+ recombinants are 89+11=100

Total recombinants = 200

RF = (200/1000)*100 =20%

% RF = Map unit distance

The order of genes is -----

sm--------20 m.u.--------ye---10m.u.----st

Order of genes is sm + st / + ye +