Use this information to answer Questions 23, 24, 25, 26 below Two traits are exa

Question

Use this information to answer Questions 23, 24, 25, 26 below Two traits are examined simultaneously in a cross of two pure-breeding pea plant varieties. Pod shape can either be swollen or pinched. Seed color can be either green or yellow. A plant with the phenotypes pinched and green is crossed with a plant that is swollen and yellow. The resulting F1 plants are self-crossed to produce the F2. A total of 320 F2 progeny are phenotypically categorized as: 180 swollen, yellow 60 swollen, green 60 pinched, yellow 20 pinched, green 23. Based on the results above, what phenotypic ratio is observed for pod shape in the F2? 24. What is the Final Phenotypic Assortment Ratio observed in the F2? 25. Which of the following is the most probably Genotype of the F2 swollen, green progeny? 26. If one of the pinched, green F2 progeny were backcrossed to an F1 plant, how many progeny A. 1:1B. 3: C. 1:2:1 D. none of these A. 1:1:1:1 B. 3:1:3:1 C. 9:3:3:1 D. none of these out of 144 would you expect to be pinched, yellow? Pick the closest number A. 18 B. 27 C. 36 D. 54

Explanation / Answer

23.
Total progeny = 320
Swollen = 180 + 60 = 240
Pinched = 60 + 20 = 80
= 3:1 ratio

24.
Phenotypic ratio = 180:60:60:20
= 9:3:3:1

25.
Swollen = AA or Aa
Green = bb
Swollen green progeny = AA bb or Aabb

26.
Green piched F2 = aabb
F1 plant = AaBb
Cross: AaBb X aabb
Gametes: (AB)(Ab)(aB)(ab) X (ab)
Progeny = AaBb Aabb aaBb aabb
Pinched green = 1/4
= 144/4
= 36

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