5.1 The biological realities of human reproduction drive the dynamics of kinship. Other living things have different dynamics…and there are a dizzying array of reproductive methods and strategies, what in biology class we called “life cycles,” remember? There is something called parthenogenesis…which is asexual reproduction. That means, producing offspring without first shuffling of 2 sets of genes, a mother’s and a father’s…producing what we would call today clones. This happens naturally in many lower forms of animals, and even in some crustaceans, fishes, and reptiles. In humans, identical twins are genetically the equivalent of clones.
5.2 There is even something called paedogenesis, or “born pregnant.” This occurs in some insects…but not in gerbils as is widely believed…altho on Star Trek, it was the case with tribbles! Again, this is asexual or parthenogenic reproduction, and all the offspring are clones. For example, within the body of a pregnant aphid (the grandmother generation), the fetal aphids (the mother generation) are themselves, within their yet-to-born bodies, producing the daughter generation. As you can well imagine, this is primarily to save time.
5.3 You might wonder then, in all of the Natural World, can there be 2 individuals that, while not identical clones, are still more closely related than full siblings would be in human terms? Well, there’s always incest if course…in some animals there are behavioral instincts that work against it, in others there are not. With the selective breeding of domesticated animals, such “back breeding” is an invaluable genetic tool. But outside of that, there are indeed cases of naturally occurring “closer-than-siblings”…and those with bees occur even without the mating of 2 related individuals. The resulting offspring are called “super-sisters.”
5.4 First, human genetics…Chart B1 shows the genetic make-up of 2 human sisters, Alice and Zelda. Each of the numbered tabs represent a gene…to make it simple, I show 8 genes…but humans have about 20,000, and bees 10,000.
5.5 Looking at Alice’s mother, she has 16 genes…2 sets of the same 8 genes…the pink ones she got from her mother, the blue from her father. To make Alice, her mother produces an egg, that has just 8 genes, randomly chosen from her pink group and her blue group (the grey arrows.) The same thing happens with Alice’s father…he has yellow genes from his mother, green from his father, and a random mix of those form a sperm cell. Together, the egg and the sperm constitute Alice and her genetic make-up.
5.6 With Alice’s sister Zelda, egg and sperm are formed the same way, from the same set of parental genes, but with a different random mix of the pink, blue, yellow, and green. Thus, the white tabs in the middle show stars where the sisters share the same genes. With only 16 genes they could share 1 or 2…or even 14 or 15…but with 20,000, it averages very close to ½, as I have illustrated.
5.7 Now we do it again, this time with bees, and you’ll notice a difference. Bee 1 and Bee 2 are not clones…they are sexually produced sisters, since each has the same mother and father. But their father was produced from an unfertilized egg and he has only one set of genes. Thus, all the sperm cells he produces will be clones of himself, and of each other…he simply has no other genetic material with which to mix-and-match.
5.8 And actually, his 8 genes should not all be yellow, but a mix of yellows and greens (half from his mother’s mother, half from his mother’s father.) I made them all yellow to emphasize the point that the 2 super-sisters will automatically share half their genes…the entire half that each gets from their father. They will also share, as do humans, roughly half of those they get from their mother, bringing their total shared inheritance to 3/4, as you can see in the center white tabs with stars…of their 16 genes, they share 12…super-sisters!
5.9 Next week, halves and doubles. Till then, stay busy…
Copyright © 2011 Mark John Astolfi, All Rights Reserved