What are chromosomal disorders? Describe the cause and symptoms of Down's, Klinefelter's and Turner's syndromes.

How to lay out the answer. Follow the frame, then write it in your own words.

1 · Define chromosomal disorders. Disorders from the absence, excess or abnormal arrangement of chromosomes.
2 · Explain how they arise. Failure of chromatids to separate gives aneuploidy; failure of cytokinesis gives polyploidy.
3 · Down's syndrome. Trisomy 21, 47 chromosomes; short, small round head, furrowed tongue, palm crease, delayed development.
4 · Klinefelter's syndrome. 47, XXY male; masculine but with gynaecomastia; sterile.
5 · Turner's syndrome. 45, XO female; rudimentary ovaries, sterile, lacks secondary sexual characters.
6 · Link to real life. Amniocentesis can detect these disorders before birth.
7 · Close in one line. So one extra or missing chromosome can change body form, development and fertility.

Scoring tip: A three-column table (cause, karyotype, two features) scores well and saves time.