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Biology · 2026 · 5 marks
CBSE 2026 · Region 2 · Set 2 · Q32
(a) (i) Identify the structure shown above and name the process taking place. (ii) Write the source of energy for the process and list the enzymes…
(i)
Identify the structure shown above and name the process taking place.
(ii)
Write the source of energy for the process and list the enzymes involved.
(iii)
Mention the difference in the process based on polarity. What terms are used for such synthesis?
(iv)
Redraw the structure after completion of the process and label the newly synthesised parts.
(i)
How would you find out whether a given tall garden pea plant is homozygous or heterozygous ?
Substantiate your answer with the help of Punnet square.
(ii)
Given below are F2 phenotypic ratios of two independently carried monohybrid crosses.
(1)
$\displaystyle 1$:$\displaystyle 2$:$\displaystyle 1$
(2)
$\displaystyle 3$:$\displaystyle 1$
Mention what does each ratio suggest.
Marking-scheme solution
(i)
• Structure - Replication fork
• Process - DNA Replication
(ii)
• Source of Energy - Deoxyribo nucleoside triphosphates
• Enzymes - DNA dependent - DNA polymerase / helicase / topoisomerase /
permease / DNA Ligase
(iii)
• According to the template strand with polarity $\displaystyle 3$' – $\displaystyle 5$' - new DNA is
synthesized continuously but in the strand with polarity $\displaystyle 5$' - $\displaystyle 3$'- new DNA is synthesized in short fragments
• Continuous synthesis, discontinuous synthesis.
(iv)
(i)
By crossing the given tall garden pea plant with a recessive parent / Test Cross
(I)
TT (dominant phenotype, genotype unknown) X tt (homozygous recessive)
Result : All pea plants are tall
Interpretation : Unknown plant is homozygous
(II)
Tt (dominant phenotype, genotype unknown) X tt (homozygous recessive)
Result : $\displaystyle 50$% pea plants are tall and $\displaystyle 50$% plants are dwarf
Interpretation : Unknown plant is heterozygous
(ii)(1)
$\displaystyle 1$:$\displaystyle 2$:$\displaystyle 1$ ratio suggests incomplete dominance
(2)
$\displaystyle 3$:$\displaystyle 1$ ratio suggests complete dominance
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CBSE Class 12 Biology past-paper question from the 2026 board exam, with the answer as CBSE’s own marking scheme gives it. Where our answers come from.