Sexual Reproduction Activity Build a Karyotype with Chromosomes from Gametes


Create a baby from the chromosomes in gametes!

Grades 7 and Up


Kids LOVE this activity! This karyotyping activity clearly shows that gametes have half the number of chromosomes as the parent, and they combine to make a complete zygote. Students are excited to find out if their baby koala is a male (called a buck) or a female (called a doe)! This is a fun – and minimally awkward – way to teach sexual reproduction!

This activity reinforces:

  • Sexual reproduction requires two parents.
  • Gametes have half the number of chromosomes as the parents.
  • Gametes combine to make a zygote in the process of fertilization.
  • Chromosomes have homologous pairing and differ based on size and banding pattern.
  • A karyotype is an organized map of chromosomes.
  • Different organisms have different numbers of chromosomes.
  • XX makes a female koala offspring and XY makes a male koala offspring.

In this activity, students will:

  • Read background information about sexual reproduction, including the terms gameteszygotefertilizationspermegg, and homologous chromosomes.
  • Obtain a koala egg and a koala sperm. (We do this activity in pairs, so one student gets the male gamete and the other gets a female gamete.)
  • Cut out the chromosomes and match the homologous pairs using a provided key. (Koalas have 16 total chromosomes, so the cutting is minimized compared to a human karyotype.)
  • Paste the homologous chromosome pairs onto their karyotype page and identify whether it is male or female.
  • Answer follow-up questions on a worksheet.


  • Introductory reading passage with koala chromosome key
  • Koala egg and koala sperm (2 versions to make male and female babies)
  • Blank koala karyotype
  • Follow-up questions worksheet
  • Helpful teacher notes

NGSS Standards:

  • MS-LS3-2
  • Science & Engineering Practice: Developing and using models

Teacher Notes:


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