Mendel's law of segregation states that organisms inherit two copies of each gene and that

Gene segregate

Explanation:

As per the Mendel's law of segregation, an organism that inherit two copies of each gene segregate at the time of cell division (gamete formation) in a way that each allele of a gene can combine with any other allele to form a new genotype during fertilisation stage.

For example a red color flower with genotype "RR" and a white color flower with genotpe "rr" segregate at the stage of gamete formation. Thus each "R" allele of red flower can combine with each "r" allele of white flower thereby producing heterozygous red flower with genotype "Rr" during fertilisation stage.