Read Aneuploidy through Karyotypes
Karyotypes reveal chromosome-number changes and help distinguish chromosomal disorders from gene mutations.
Chromosomal Disorders is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Read the chromosome count
Down syndrome is trisomy 21. A male has 44 autosomes plus XY and the extra chromosome 21: 45+XY (47 total). Turner syndrome is usually 45,X, with short stature and gonadal dysgenesis rather than tall stature.
Separate mutation scales
Aneuploidy and structural chromosome changes are chromosomal/genomic disorders. Base substitutions and frameshifts are gene-level mutations.
Trace nondisjunction outcomes
A normal egg contributes X. Abnormal sperm carrying XX, YY, XY or no sex chromosome can produce XXX, XYY, XXY or XO respectively. A YO zygote cannot form from a normal egg.
OlympIQ exam lens
- ✓Down male: 45+XY.
- ✓Turner: 45,X; not characteristically tall.
- ✓Frameshift/substitution are gene-level changes.
- ✓Start with the chromosome supplied by the normal gamete.
- ✓A normal X-bearing egg rules out YO.
Read the notation carefully: 45+XY means 45 autosomes plus XY, 47 chromosomes total.
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