Sexual reproduction in nature is common. It is the way most life-forms procreate. To procreate is to produce offspring.
In sexual reproduction, each parent provides half the chromosomes of their offspring. Genes are carried in the chromosomes. Genes are made up of DNA, which tells our bodies how to grow and work. Over generations, sexual reproduction keeps the genes mixed. It shuffles the DNA cards. That gives sexual reproducers genetic diversity. That means variation of genes. Genetic diversity is a benefit in nature. It can help organisms adapt more successfully to changing environments.
Not all life-forms reproduce sexually. Some do so asexually. About 70 vertebrate species procreate asexually. Vertebrates are animals with backbones. Many less complex animals produce offspring this way, too. These animals use "all the chromosomes they have" to produce offspring on their own, Peter Baumann says. He is a molecular biologist. These scientists study how cells work at the level of the molecule.
A Disease that Kills One Could Kill All
In asexual reproduction, the offspring have the same genes as the mother. They are genetically identical. Basically, they are clones! Because of that, they're more vulnerable. A disease or an environmental change that kills one could kill all of them.
But there's a twist in the case of the genus Aspidoscelis. This is the whiptail lizard. It reproduces asexually also.
Baumann and his colleagues have been studying this species. They work at the United States' Stowers Institute for Medical Research in Kansas City, Missouri. The lizards are all female. They are also parthenogenetic. That means no males take part in reproduction. Their eggs develop into embryos without being fertilized by a male.
Whiptails Have Surprising Genetic Variety
Baumann's team discovered something curious. Before the eggs form, the females' cells change. They gain twice the usual number of chromosomes. This means that the eggs get a full chromosome count, not just half. It also means they get genetic variety. This is known as heterozygosity. The whiptails end up with heterozygosity rivaling that of sexually reproducing lizards.
Baumann believes he knows why. At some time in the past Aspidoscelis lizards had "a hybridization event," he explains. Females of one species did something unusual. They mated with males of another species. This gave whiptails heterozygosity. This heterozygosity has been preserved by asexual reproduction. In a sense, the lizards keep cloning themselves. It's a genetic-diversity advantage. Today's Aspidoscelis females still enjoy and replicate it.