If you look at the Punnett Square in the previous post, you will see that the first line and the third line are identical. And the second and fourth line are identical. Because the pastel parent produces only two different types of gametes instead of four. In cases like this, it saves time and energy to simply drop the third and fourth line and go with a 4x2 grid instead of a 4x4 grid.

An cross of Aa Bb x aa bb can be shrunk to a 4x1 grid, because the aa bb parent produces only a b gametes.

A cross of Aa bb x aa Bb can be shrunk to a 2x2 grid. Because the Aa bb parent produces two types of gametes: A b and a b. And the aa Bb parent produces two types of gametes: a B and a b.

Paul Hollander

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