The baby has the mother's eyes but the father's hair colour; the nose is like the grandfather's and the mouth is like the grandmother's. These are other possible combinations are caused by genetic inheritance. The genes transmitted by the father combine with genes in the mother's egg, forming a single cell that will turn into a new human being. 

Through cell division during the baby's growth inside the uterus, the genes will expand, and the dominant ones will impose themselves over the recessive ones. In the case of twins, the physical resemblance results because they share the same genes.

Identical and fraternal twins 

It is estimated that one in 70 childbirths produces either identical (monozygotic) or fraternal (dizygotic) twins. Identical twins have the same genes and therefore are like and of the same sex. They come from one fertilized egg. In some cases, twins share the placenta. Fraternal twins, on the other hand, are the same in age but not in genetic material. They come from two eggs that are released at the same time and are fertilized by different sperm.

Resemblances 

If one observes different vertebrate embryos, the similarities between them are notable. These resemblances reveal that they are all descended from a common ancestor. The development of the body parts is marked by very similar genes. Morphologically, all embryos possess a segmented tail, a heart with two cavities and gill. The greatest difference appears in fish, which retain the gill. The other groups, one of the gills transform into the ear canal and the other into the eustachian tube. In spite of the changes in outer appearance, the observable patterns of internal organization tend to be preserved.

Made-to-order babies 

Genetics is also used to find out which genes a baby will have. If the mother and the father have a defective gene, they could opt for pre implantation genetic diagnosis to make sure that the baby will be born healthy. This controversial method can determine if the embryo will be a boy or a girl, and it also prevents hereditary health risks. In pre implantation, the mother takes a drug to produce eggs, which are then fertilized with a sperm from the father. Later a DNA test is done on the embryo's cells, and then two or three healthy Anders as selected and implanted in the mother's uterus.

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