In sexual reproduction—the way most life-forms procreate—each parent provides half an offspring's chromosomes. Over generations, this mating and procreating shuffles the DNA deck, giving sexual reproducers a genetic diversity that helps them adapt to changing environments.

By contrast, asexual reproducers—some 70 vertebrate species and many less-complex organisms—"use all the chromosomes they have" to solitarily produce offspring that are genetic clones, molecular biologist Peter Baumann says. Because the organisms are genetically identical, they're more vulnerable: A disease or an environmental shift that kills one could kill all.

But there's a twist in the case of the genus Aspidoscelis, the asexually reproducing whiptail lizards that Baumann and his colleagues have been studying at the United States' Stowers Institute for Medical Research in Kansas City, Missouri. The lizards are all female and parthenogenetic, meaning their eggs develop into embryos without fertilization.

But before the eggs form, Baumann's team discovered, the females' cells gain twice the usual number of chromosomes during meiosis. This results in a standard pair of chromosones derived from two sets of pairs. So the eggs get a full chromosome count and genetic variety and breadth (known as heterozygosity) rivaling that of a sexually reproducing lizard.

Why does this occur? Because long ago, Baumann says, lizards of the genus Aspidoscelis had "a hybridization event"—that is, females of one species broke form and mated with males of another species. Those outlier liaisons gave whiptails robust heterozygosity, which has been preserved by the identical replication—essentially, cloning—that occurs in asexual reproduction. It's a genetic-diversity advantage that today's females still enjoy and propagate.

 

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.