Karyotypes and non-disjunction – building a human karyogram
BiologyGeneticsAges 17–18
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Sign in to playBuild a karyogram from a cell in metaphase: drag 46 chromosomes into pairs by length, centromere position and banding, and measure the centromere index; identify trisomy 21, 18 and 13, Turner syndrome (45,X) and Klinefelter syndrome (47,XXY). Animate meiosis with non-disjunction in meiosis I or II to see n + 1 and n − 1 gametes and the zygotes they form, explore the maternal age effect on Down syndrome, and compare human chromosome 2 with chimpanzee chromosomes 2A and 2B.
Lesson: Karyotypes and chromosome number mutations
What it shows
This simulation covers karyotypes and chromosome number mutations for ages 14–18. Students build a karyogram by pairing homologous chromosomes by length, centromere position and banding, measure each chromosome and identify trisomies, Turner syndrome and Klinefelter syndrome. They then follow one chromosome pair through meiosis, cause non-disjunction in meiosis I or II and predict the zygotes formed. Further screens show the maternal age effect on Down syndrome using a published risk model and the fusion that formed human chromosome 2. Bands are schematic, not real G-banding images, and only one pair is followed through meiosis.
How to use
In Karyogram, choose a Cell to karyotype, then drag each chromosome into its slot, or tap it and tap a slot; tap a chromosome to add its measurements to the table, or use Hint and Auto-sort. In Non-disjunction, choose Meiosis in, the Chromosome pair and Non-disjunction in, then use Next or Play and tap a gamete. In Maternal age, move the Mother's age slider. In Human and chimp, press Join the chromosomes.
Parameters you can change
- Starting screen Karyogram, Non-disjunction in meiosis, Maternal age, Human and chimp
- Cell to karyotype Typical female, Typical male, Trisomy 21, Trisomy 18, Trisomy 13, 45,X, 47,XXY, Mystery patient
- Meiosis in (Non-disjunction screen) Mother (egg), Father (sperm)
- Non-disjunction in None (normal meiosis), Meiosis I, Meiosis II
- Chromosome pair followed Chromosome 21, Sex chromosomes
- Mother's age (Maternal age screen) 15–50 years
Questions to explore
- Why does non-disjunction in meiosis I give four abnormal gametes, but non-disjunction in meiosis II gives only two?
- How can a karyogram show the difference between a person with Turner syndrome and a person with Klinefelter syndrome?
- What evidence suggests that human chromosome 2 formed by the fusion of two ancestral chromosomes?
