Proteins that assist in the movement of substances across can be classified into two types which are:
<h3>What are Proteins?</h3>
These are biological molecule which consists of amino acid sequences and are involved in metabolic activities in the body.
They are also found in cells and help in the selective movement of molecules in and out of the cell.
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A. In prophase I, tetrads of homologous chromosomes form and crossing over occurs
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This is referring to meiosis, which happens just once to make reproductive cells, unlike mitosis which is just simple copying.
In mitosis, one cell splits into two, but the number of chromosomes doesn't change. The original cell makes two copies of its chromosomes and divides them up.

In <em>meiosis</em>, however, our cell doesn't bother making those two copies. It just takes what it has and divides it between two new cells.
There is going to be a 25% chance of it being heterozygous unless both parents are heterozygous then if so you do happen to have to heterozygous parents it will be 100% heterozygous.