Question

(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…

Accepted Answer

(a) Law of independent assortment: It states that when two pairs of traits are combined in a hybrid segregation of one pair of characters is independent of the other pair of characters Parents phenotype - Axial violet flower X Axial violet flower Parents Genotype - AaVv X AaVv Axial violet – 9 Axial white – 3 Terminal violet – 3 Terminal white – 1 Non-parental recombination in the F2 progeny shows independent assortment of characters. OR • 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”.

(a)
State Mendel's law of independent assortment.
(ii)
Explain this law by taking the example of a cross between two heterozygous parents of pea plants with respect to flower colour and flower position using Punnett Square.

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