Ruth Hanessian, co-organizer of Science Cafe, and Dr. Tammatha O’Brien, chat after Dr. O’Brien’s presentation on The Genetics of Sex

Report from the Field, author Isabelle Trocheris

Bacteria, which reproduce by a simple cell division, have been very successful, says Dr. Tammatha O’Brien, Director of Master of Professional Studies in the Applied Entomology Program at the University of Maryland. For example, half an ounce of soil can contain many billions bacterial cells, more than there are people in the world. But, on the other hand, sexual reproduction, which is used by most higher organisms including humans, brings diversity through genetic variation.

By combining half of the genes of two different individuals to give birth to a new one, sexual reproduction gives rise to this variation. At the same time, having two different sets of the same genes allows for the development of a healthy individual even if one copy of a gene is defective as seen in recessive traits. To maximize the quality of their offspring’s DNA, diverse female vertebrates have been shown to select strength and beauty in their mates. Other more subtle mechanisms, such as smell, allow some, like mice and possibly humans, to go farther to insure diversity in the genes controlling part of the immune system.

But sometimes variation is a double-edged sword, notes O’Brien. For example, a mutation in the hemoglobin gene confers a protection from malaria but can lead to sickle cell anemia if two parents pass this gene on to their children.