Mendel law of inheritance include laws of segregation. It is usually considered as second law among law’s of inheritance by Mendel.
Mendel’ second law of inheritance state that when one organism making gametes then all allele distribute themselves as only one copy of them reach to each gamete.
At the time of Mendel, technologies were not so advanced neither too much knowledge about genetics was there. Beside these all, mendel law of segregation has been proved by meiotic cell division.
Law of segregation is all about the distribution of genes in the gamers. We know there are two copies of each gene is there in the cell. At the time of gamete formation meiotic cell division occurs and each gamete received only one copy of gene. Later when fertilization occur, egg and sperm (in case of human) both bring their copy of gene (egg from female and sperm from male), both gene copies meet again and restore the diploid nature of cell, after the process of fertilization.
So, we can say mendel’s second law (law of segregation) is all about the gamete formation and segregation of alleles from parents to gametes. This law is applicable on almost all haploid organisms those do gamete formation and have fertilization process in their life cycle.
Some time Mendel’s law of segregation is called as the first law of inheritance, this is because the law of dominancy (which is the first law) is so well followed, it is named as principle of genetics (i.e. principle of dominancy) and second law of mendel is termed as first law of mendelian genetics.