Grandchildren are genetically related to their grandmothers; grandchildren inherit some of their grandmothers’ chromosomal genes, but not their grandmothers’ cytoplasmic genes.
The main genetic material of human beings is DNA, which is mainly found in human chromosomes, and a small part of it is also found in the cytoplasm. What people usually call heredity is the process of passing chromosomal and cytoplasmic genes from parent to offspring, accompanied by the transmission of inherited traits.
Grandmother mainly provides the egg cell, which develops into the father after combining with grandfather’s sperm to form a fertilized egg. All of the grandmother’s cytoplasmic genes are passed on to the father, but the grandfather’s cytoplasmic genes are not passed on to the father; this is matrilineal inheritance.
After that, the father randomly selects half of the chromosomes that go into the sperm to be passed on to the grandchildren. This half of the chromosomes will also have chromosomes from the grandmother. Therefore, the grandson is inherited from the grandmother, but the father’s cytoplasmic genes from the grandmother are not passed on to the grandson.