← Exit
  1. Watch
  2. Word of the day
  3. Predict
  4. Read the paper
  5. Exit ticket

Coquita the Crocodile, College

Video 1. Virgin birth in a crocodile

Coquita is an American crocodile who lived alone at a reptile park in Costa Rica for 16 years. In 2018 she laid 14 eggs, and one held a fully formed baby with no father’s DNA. Scientists call this parthenogenesis.

Video 2. Coquita’s virgin birth is not a clone

Coquita’s baby got all of its DNA from her, but the baby was not a clone. Her egg ended up with two matching copies of almost every gene instead of one copy from each parent. Where Coquita carried one working copy and one broken copy of a gene, her baby got two of the same.

The Parthenon in Athens
The Parthenon in Athens took its name from Athena Parthenos, “Athena the Virgin.”

Your word of the day is

par-theh-no-JEN-uh-sis

partheno-maiden, virginfrom Greek parthénos
-genesisorigin, birthfrom Greek génesis

An egg develops into a baby without sperm fertilizing the egg.

Close-up of an American crocodile’s snout and teeth

A heterozygous site is a spot where Coquita carried two different versions of a DNA letter. A clone would keep 100% of those sites mixed.

Before you read the paper, make a guess. What percent of Coquita’s heterozygous sites stayed heterozygous in her baby? Write one sentence on why you think so.

Hint

In video 2, Raven says that at every spot where Coquita carried one working copy and one broken copy, her baby got two of the same.

A scientist preparing DNA samples for testing

Read the paper

Booth and others, “Discovery of facultative parthenogenesis in a new world crocodile,” Biology Letters, 2023. The paper is free to read.

Warren Booth’s team sequenced the genomes of Coquita and her baby. Table 1 of their paper counts the spots where Coquita carried two different versions of a DNA letter (her heterozygous sites) and how many of those spots stayed mixed in her baby. Each dataset uses sites spaced at least 10,000, 25,000 or 50,000 DNA letters apart.

Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A model of a DNA double helix

Table 1 of the paper gives three datasets, with sites spaced 10,000, 25,000 or 50,000 DNA letters apart.

In the 10,000-letter dataset, 152 of Coquita’s 5,015 mixed sites stayed mixed in her baby. What percent stayed mixed? ____

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A wild American crocodile resting on a riverbank

In the 25,000-letter dataset, 76 of Coquita’s 2,023 mixed sites stayed mixed in her baby. What percent stayed mixed? ____

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A drawing of a DNA double helix

In the 50,000-letter dataset, 34 of Coquita’s 1,026 mixed sites stayed mixed in her baby. What percent stayed mixed? ____

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A scientist loading DNA samples into a gel to test them

Why would the Coquita research team run the same test with sites spaced 10,000, 25,000 and 50,000 DNA letters apart?

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A wild American crocodile in a river in Costa Rica

If Coquita’s egg had fused with the first polar body (central fusion), the baby would keep more than 33% of its mother’s mixed sites. If it fused with the second polar body (terminal fusion), it would keep less.

Which mechanism do the Table 1 data support?

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A crocodile resting beside a pond

All of the Table 1 data come from a single baby that grew in one egg.

Which conclusion do the Table 1 data from Coquita’s single baby support best?

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
The head of an American crocodile

Figure 2 of the paper maps the reptile lineages with documented facultative parthenogenesis and connects them to birds.

Which origin of facultative parthenogenesis do the authors of the Coquita paper favor?

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
An American crocodile at a reptile park

Which finding would best support a single shared origin of facultative parthenogenesis over separate origins?

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A close-up of a crocodile’s eye

The authors suggest zoos test eggs from isolated females instead of throwing them away.

What should a zoo caring for a vulnerable species do with eggs from females kept alone?

See the table
Dataset spacingCoquita’s mixed sitesStill mixed in the babyPercent still mixed
10,000 letters5,015152
25,000 letters2,02376
50,000 letters1,02634
A close-up of a crocodile in the water

Table 1 compares Coquita’s heterozygous sites with the same sites in her baby.

Which statement best summarizes what Table 1 of the Coquita paper shows?

A crocodile lying still on rocks by the water

Which question can’t Table 1 of the Coquita paper answer?

A chart of all the chromosomes in one human cell

Lesson complete

Today’s word

parthenogenesis

par-theh-no-JEN-uh-sis

An egg develops into an embryo without fertilization.

Back to the lessonStart over
Up nextunisexualSome species are all female and they still make babies
Sources
  1. Booth and others, Biology Letters, 2023
  2. Card and others, Scientific Reports, 2021 (king cobra)
  3. Vision and Change core concepts and competencies, as summarized in Brownell and others, CBE Life Sciences Education, 2014
  4. Word origins from Dictionary.com: parthenogenesis, homozygous, gene, hydrogen
  5. Mark Cartwright, “Parthenon,” World History Encyclopedia
  6. Spanish and French spellings from Wiktionary