K.C.S.E Biology Q & A - MODEL 2000PP1QN12

K.C.S.E Biology Q & A - MODEL 2000PP1QN12

 The chart below represents the result of successive crosses, staring with redflowered plants and white flowed plants and in which both plants are pure breeding.

(a) What were parental genotype? Use letter R to represent the gene for red colour and r for white colour
(b) (i) What was the colour of the flowers in the first filial generation?
(ii) Give a reason for your answer in b (i) above
(c) If 480 red flowered plants were obtained in the second filial generation, how many F2 plants and white flowers? Show your working.

answers

(a) RR and rr
(b) (i) red
    (ii) complete dominant; i.e Rd dominant/ white recessive
(c) Ratio of filial generation: 3: 1
(I.e. in every 4 flowers 3 are red 1 is white
Therefore 480 red flowers means ¾ of the total number
Total number of flowers (480 x 4)/3 = 640
 So ¼ of 640 flowers are white in F2 plants
    ¼ x 640 = 160 flowers