What is combinational variability? Give examples. What are the sources of combinational variability?

Combinational variability is the variability of the offspring, due to the emergence of new combinations (combinations) of parental genes.
Sources of combinational variability are: crossing over, independent chromosome divergence in the anaphase I of meiosis, a random combination of gametes during fertilization. The first two processes provide the formation of gametes with different combinations of genes. Accidental fusion of gametes leads to the formation of zygotes with various combinations of genes of both parents. As a result, hybrids have new combinations of parental traits, as well as new traits that parents did not have. The structure of the genes does not change.
An example of combinative variability is the birth of children with I or IV blood groups in heterozygous parents who have blood groups II and III (new signs differing from parental ones appeared in the offspring). Another example would be the appearance of flies with a gray body, embryonic wings and a black body, normal wings when crossing a diheterozygous Drosophila (gray body, normal wings) with a black male having embryonic wings. In this case, the offspring as a result of crossing over appeared new combinations of traits of parents.

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