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Explain why variations are observed in the off springs of sexually reproducing organisms ?

When homologous chromosomes come together during prophase I of meiosis, they exchange bits of DNA with each other. This crossing-over results in new gene combinations and new chances for variety. Crossing-over is one way of explaining how a person can have red hair from his mother’s father and a prominent chin from his mother’s mother. After crossing-over, these two genes from two different people wound up together on the same chromosome in the person’s mother and got handed down together.

Independent assortment occurs when homologous chromosomes separate during anaphase I of meiosis. When the homologous pairs of chromosomes line up in metaphase I, each pair lines up independently from the other pairs. So, the way the pairs are oriented during meiosis in one cell is different from the way they’re oriented in another cell. When the homologous chromosomes separate, many different combinations of homologous chromosomes can travel together toward the same side of the cell.fertilization produces random combinations of genetically diverse sperm and eggs, creating virtually unlimited possibilities for variation. That’s why every human being who has ever been born — and ever will be born — is genetically unique. Well, almost. Genetically identical twins can develop from the same fertilized egg, but even they can have subtle differences due to development.


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