Sexual reproduction is the way most life-forms procreate, or produce offspring. Each parent provides half the chromosomes of their offspring. Chromosomes are where the genes are carried. Genes are made up of DNA, which tells our bodies how to grow and function.

Over generations, sexual reproduction shuffles the DNA cards. That gives sexual reproducers genetic diversity, or many combinations of genes. It is believed that genetic diversity can help organisms adapt more successfully to changing environments.

Genetic Clones

Not all life-forms reproduce sexually, however. Some reproduce asexually. About 70 vertebrate species—animals with backbones—and many less-complex organisms procreate in this manner. These animals use "all the chromosomes they have" to solitarily produce offspring that are genetic clones, molecular biologist Peter Baumann says. Molecular biologists study the functioning of cells on the molecular level.

In asexually reproducing species, offspring have the same genes as the mother. They are genetically identical. Because of that, they're more vulnerable: A disease or an environmental shift that kills one could kill them all.

But there's a twist in the case of the genus Aspidoscelis. This is the asexually reproducing whiptail lizard. Baumann and his colleagues have been studying this species at the United States' Stowers Institute for Medical Research in Kansas City, Missouri. The lizards are all female. They are parthenogenetic. That means that their eggs develop into embryos without being fertilized by a male.

But Baumann's team discovered something curious. Before the eggs form to create a new offspring, the females' cells gain twice the usual number of chromosomes. This means that the eggs get a full chromosome count. The one pair of chromosones comes from two sets of pairs. It also means they get genetic variety and breadth, known as heterozygosity. In fact, the eggs have heterozygosity like that in sexually reproducing lizards.

Whiptail Females Did Something Unusual

Baumann believes he knows why this occurs. At some time in the past lizards of the genus Aspidoscelis had "a hybridization event," he explains. Females of one species did something unusual and mated with males of another species. This gave whiptails robust heterozygosity. This has been preserved by the identical replication—essentially, cloning—that occurs in asexual reproduction. It's a genetic-diversity advantage that today's Aspidoscelis females still enjoy and replicate.