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.

How an Asexual Lizard Procreates Alone

Without females, lizards in the Aspidoscelis genus, like this New Mexico Whiptail (Aspidoscelis neomexicana), reproduce asexually. Unlike other animals that produce this way, however, their DNA changes from generation to generation.

asexual reproduction
Noun

reproduction that requires only a single organism, without a union of individuals or gametes.

chromosome
Noun

strand of DNA and associated proteins in the nucleus of cells that carries the organism's genetic information.

clone
Noun

cell or group of cells that is genetically identical to its ancestor cell or group of cells.

DNA
Noun

(deoxyribonucleic acid) molecule in every living organism that contains specific genetic information on that organism.

generation
Noun

group in a species made up of members that are roughly the same age.

genetic
Adjective

having to do with genes, inherited characteristics or heredity.

genetic diversity
Noun

difference or variety of units of inheritance (genes) in a species.

heterozygous
Adjective

having two different alleles for the same gene

heterozygous
Adjective

having two different alleles for the same gene

hybrid
Noun

the end result of two different sources of input.

meiosis
Noun

type of cell division in which the daughter cells have half the number of chromosomes as the parent cell; also known as reduction division

meiosis
Noun

type of cell division in which the daughter cells have half the number of chromosomes as the parent cell; also known as reduction division

molecular biologist
Noun
scientist who studies the structure and activity of molecules essential to life.
parthenogenesis
Noun

method of reproduction in which the organism develops a female gamete without fertilization. Common among plants and invertebrates.

procreate
Verb

to breed.

reproduction
Noun

the process of breeding.

sexual reproduction
Noun

type of reproduction in which a sperm fertilizes an egg to form a zygote

vertebrate
Noun

organism with a backbone or spine.