(a) (i) State Mendel's law of independent assortment. (ii) Explain this law by taking the example of a cross between two heterozygous parents of pea…

Non-parental recombination in the F2 progeny shows independent assortment of characters.

• Griffith selected ‘S’ strain and ‘R’ strain bacteria Streptococcus

pneumoniae, ‘S’ strain – Virulent causes pneumonia, ‘R’ strain –

Non-virulent does not cause pneumonia

‘S’ strain

𝐼𝑛𝑗𝑒𝑐𝑡 𝑖𝑛𝑡𝑜 𝑚𝑖𝑐𝑒 → mice die

‘R’ strain

𝐼𝑛𝑗𝑒𝑐𝑡 𝑖𝑛𝑡𝑜 𝑚𝑖𝑐𝑒 → mice live.

‘S’ strain (heat-killed)

𝐼𝑛𝑗𝑒𝑐𝑡 𝑖𝑛𝑡𝑜 𝑚𝑖𝑐𝑒 → → mice live

Heat killed ‘S’ strain + ‘R’ strain (live)

𝐼𝑛𝑗𝑒𝑐𝑡 𝑖𝑛𝑡𝑜 𝑚𝑖𝑐𝑒 → mice die.

Griffith concluded that the ‘R’ strain bacteria had somehow been transformed by the heat killed ‘S’ strain bacteria.

• They purified biochemicals (Proteins, DNA, RNA etc.) from the heat

killed ‘S’ cells and the fractions were added individually to the culture of the live ‘R’ cells,

DNA was able to cause transformation of ‘R’ cells into ‘S’ cells/they found that protein digesting enzyme or RNA digesting enzymes did not affect transformation or digestion with DNase did inhibit transformation indicating that the transforming substance is not a protein or RNA,

This suggests that the DNA is the “genetic material”.