Kaguya the Mouse

Predict

A baby mouse usually comes from one egg and one sperm. Scientists in Tokyo tried to grow a mouse from the DNA of two mouse eggs and no sperm. Could two eggs and no sperm ever make a living mouse?

Circle one. Yes / No

Why?

Watch

1. 2 eggs can make a mouse, with some helpyoutube.com/shorts/1ymhrjaj6e0

Word of the day

Imprinting (im-PRIN-ting). In genetics, a tag on a gene that marks which parent the gene came from. The tag controls whether that copy of the gene switches on.

• A printing press presses inked letters onto paper. Print comes from an Old French word meaning “to press.”
• In animal behavior, ducklings imprint on the first large moving object they see, usually their mother. English took the word imprinting in 1937 for this kind of fast learning.

Bonus word. Genome (JEE-nohm) means a full set of an organism’s chromosomes. It comes from German Genom, a blend of Gen, “gene,” and Chromosom, “chromosome.” Scientists call this lesson’s word genomic imprinting.

Questions

1. Eggs and sperm carry the same genes, yet embryos made from two ordinary eggs stop growing. In the video, Raven talks about a growth gene and the piece of DNA that holds its switch. She says dad tags often push growth up. Why does a two-egg embryo stop growing? Go step by step, and use the growth gene as your evidence.

   Hint. Which tag can an egg never put on the growth gene’s switch? What does the switch do without that tag?

2. Kaguya had no dad. Her DNA came from the eggs of two different female mice, a newborn and an adult. Why isn’t Kaguya a clone of either mouse that gave her DNA? Use how much of a full set of chromosomes each egg carried as your evidence. Then say what a clone of the adult mouse would carry instead.

   Hint. Count how many mice gave Kaguya chromosomes and how much each mouse gave.

3. MedlinePlus Genetics reports two main causes of Prader-Willi syndrome. About 70% of cases come from a missing piece of dad’s chromosome 15. About 25% come from two copies of mom’s chromosome 15 and none from dad. One cause is a missing piece of dad’s chromosome 15. The other is two copies of mom’s chromosome 15. How can two different causes lead to the same condition? Use gene tags in your answer.

   Hint. For each cause, ask which parent’s copy of the chromosome 15 genes the child is missing.

4. Kaguya’s team made about 460 tries. Those tries gave 10 live pups, and one pup grew to adulthood. Out of roughly 460 tries to make Kaguya, what percent gave a live pup? What percent gave an adult mouse?

   Hint. Divide each count by the number of tries. Then multiply by 100.

5. About 460 tries gave one adult mouse. Kaguya also needed two changes. One egg came from a newborn mouse, and that same egg was missing the growth gene switch. In 2004, scientists said this method was far from use in people. Why was the two-egg method still far from use in people in 2004? Give two reasons. Use Kaguya’s success rates and the two changes her embryo needed.

   Hint. Think about what each change would mean for a human egg.

Claim, evidence, reasoning

Going further: a switch from mom or dad

1. A switch next to the growth gene blocks it unless the switch carries a dad tag, and only sperm add that tag. In 1995, a team at Princeton bred mice missing the growth gene switch on one copy of their DNA. Mice that got the missing switch from their mother were 27% heavier than mice that got the missing switch from their father. Why were the Princeton mice heavier when the missing growth gene switch came from mom instead of dad?

   Hint. Start with dad’s copy of the growth gene. Does its switch block the gene to begin with?

2. The Princeton mice and Kaguya both come from experiments on gene tags in mice. What’s one question you’d ask next about how gene tags pass from parents to offspring?

   Hint. What do these mouse studies leave unanswered?

Exit ticket