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Biology · 2023 · 5 marks
CBSE 2023 · Region 1 · Set 3 · Q33
(a) (i) Describe the phenomenon of adaptive radiation as explained by Darwin. (ii) Is human evolution an example of adaptive radiation? Give reason…
(a)(i)
Describe the phenomenon of adaptive radiation as explained by Darwin.
(ii)
Is human evolution an example of adaptive radiation ? Give reason in support of your answer.
OR
(b)
You are given a tall pea plant and asked to determine its genotype. Name and explain the cross that you will carry out to find the possible genotype of the given tall pea plant.
Marking-scheme solution
(a) (i). Many varieties of finches (black bird) were found on the island (Galapagos),
Originally all birds had seed eating features,
. Gradually as they moved to other geographical areas,
The beak structures changed according to the food available there and many other altered beaks arose.
. Some becoming insectivorous and others remaining vegetarian,
Hence the process of evolution starting from a point and radiating to other areas of habitats is called adaptive radiation.
(ii) . No, human evolution is an example of progressive evolution and not adaptive radiation, parent species of Homosapiens have evolved from Homo habilis and to homo erectus lineage.
Test cross
Genotype of tall plant can be TT or Tt.
Cross made with pure dwarf tt.
Case I: Given tall plant - TT
If the genotype of the tall pea plant (given) was TT. Then the phenotype of all plant of this cross = $\displaystyle 100$% Tall.
CASE-II: Given tall plant - Tt
If the genotype of the tall pea plant (given) was Tt. Then phenotype of plant in this cross = $\displaystyle 50$% Tall, $\displaystyle 50$% Dwarf.
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CBSE Class 12 Biology past-paper question from the 2023 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.