All-Female Species

Predict

In some species of lizards, snakes, fish and salamanders, every adult is female. There are zero males. Could a species with no males keep having babies for thousands of years?

Circle one. Yes / No

Why?

Watch

1. Some species are all female and they still make babiesyoutube.com/shorts/usPB5PGeb0E

Word of the day

Unisexual (yoo-nih-SEK-shoo-ul). Having only one sex. Every unisexual animal with a backbone that scientists have found is all female.

• A unicycle has one wheel.
• In music, voices singing in unison share a single sound. The word comes from Latin for “of a single sound.”

Bonus word for question 2. Gynogenesis (jin-uh-JEN-uh-sis) means an egg needs sperm to start developing, but the sperm’s DNA almost never joins the egg’s DNA. It comes from gyno-, from the Greek for “woman,” and -genesis, “origin.”

Questions

1. In the video, Raven says parthenogenesis is making babies without fertilization, and the babies are near copies of their mom because there’s no dad adding DNA to the mix. A 2010 review by Kathrin Lampert and Manfred Schartl notes that mutations, small changes in DNA, still produce new genotypes in all-female species. Why does a baby made by parthenogenesis carry nearly the same DNA as her mom? And what can make her DNA a little different from her mom’s?

   Hint. Start with who adds DNA to the baby. Then think about what can change DNA from one generation to the next.

2. The Amazon molly needs sperm from a male of another species to start her eggs, but the sperm’s DNA almost never joins the egg’s DNA. A 2010 review by Kathrin Lampert and Manfred Schartl reports that some all-female salamanders also borrow sperm from males of a related species, and their babies sometimes keep part of the male’s DNA. What happens to the male’s DNA in a molly baby and in a salamander baby? And what evidence in a baby’s DNA would show that some of the male’s genes were kept?

   Hint. Start with whose DNA ends up in each baby. Then think about what you could compare a baby’s DNA against.

3. Whiptails don’t need males, yet two females sometimes act out mating behavior. Design a controlled experiment to test whether mating-like behavior between two females helps whiptails reproduce. Name the variable you change, the variable you measure, and a result that would show the behavior helps.

   Hint. Picture two groups of females that differ in one way only. Decide what you’d count in each group.

4. The Brahminy blind snake spread around the world in the soil of potted plants, and females can lay 1 to 8 eggs. Step by step, how could one Brahminy blind snake in one pot start a new population? And why would a two-sex snake species carried in the same pot be less likely to start a population?

   Hint. Follow one female and her eggs through two generations. Then think about who has to be in the pot for a two-sex species.

Claim, evidence, reasoning

Going further

1. A 2016 study by Newton and colleagues found that in New Mexico whiptail lizards, most egg cells stall partway through meiosis. The few egg cells that go on to become eggs start meiosis with twice the usual number of chromosomes, and identical copies pair up with each other. Why does pairing identical copies keep a whiptail baby’s gene mix the same as its mom’s? What does a two-parent baby get that neither a whiptail baby nor Coquita’s baby gets?

   Hint. Coquita’s baby lost almost all of her mixed gene pairs. Start with what each kind of baby gets from mom, then think about what a dad adds.

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