in a particular plant species, majority of the plants bear purple flowers. Very few plants bear white flowers. No intermediate colours are observed. If you are given a plant bearing purple flowers, how would you ascertain that it is a pure breed for that trait???? plz explain.....

To establish whether the sample is a pure breed or not, test cross would have to be carried out. The sample will be crossed with a recessive white flower sample. If the test cross yeilds all purple flowers then it is a pure breed else heterozygous.

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You need to go for a test cross.

Take the purple flowered plant and cross it with a homozygous recessive plant.

If you get all purple coloured flowers, then it is a pure breed, i.e., a homozygous dominant.

If you get purple:white in the ratio 1:1, then it is a heterozygous plant.

For more details, refer Fig. 5.5 Pg 75 in NCERT textbook.

Cheers!

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