55. At the Hogwarts School of Wizardry they use the fairly modern science of genetics to
identify potential witches and wizards. Being a witch or a wizard is dependent on the
presence of an autosomal dominant trait (the W allele). The W allele can be suppressed
by the squib allele (s), an unlinked autosomal recessive trait. Presence of two s alleles
can lead to no magical powers in individuals with the W allele. Given these observations
what fraction of the progeny from the cross outlined below will be capable of performing
magic and candidates for the Hogwarts School of Wizardry?
ww:ss x Ww:Ss
a. 1/4
b. 1/8
c. 1/2
d. 0
The correct answer is a. 1/4. In this Hogwarts genetics problem, magical ability requires the dominant W allele (Ww) without homozygous recessive ss suppressor, which masks W even in carriers. From ww:ss × Ww:Ss, progeny get Ww (1/2 probability) and Ss (1/2 probability) independently since loci are unlinked, yielding 1/4 Ww:Ss magical candidates [execute_python].
Punnett Square Analysis
Parent 1 (ww:ss) produces only w s gametes. Parent 2 (Ww:Ss) produces WS, Ws, wS, ws each at 1/4.
Combined progeny genotypes (each 1/4):
-
Ww:Ss: Magical (W present, no ss suppression)
-
Ww:ss: Squib (W suppressed by ss)
-
ww:Ss: Muggle (no W)
-
ww:ss: Muggle (no W)
Only Ww:Ss expresses magic, so fraction is 1/4 [execute_python].
Option-by-Option Explanation
| Option | Fraction | Explanation | Correct? |
|---|---|---|---|
| a. 1/4 | 25% | Matches Ww (½) × Ss (½) = ¼ magical; ss (¼ total) correctly suppresses half W carriers . | Yes |
| b. 1/8 | 12.5% | Underestimates; assumes linkage or extra condition halving Ss probability, but loci unlinked . | No |
| c. 1/2 | 50% | Overestimates; ignores ss suppression (½ Ww become squibs), predicts all Ww magical . | No |
| d. 0 | 0% | Impossible; W allele segregates normally, ss doesn’t eliminate it entirely [execute_python]. |
This suppressor epistasis pattern tests CSIR NET concepts like independent assortment and recessive masking of dominant traits.
