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UAT-UK SPEC: B4MODULE: BIOLOGYTOPIC ID: ARCH-B-04

Autosomal & Sex-Linked Pedigree Probability Trees & Conditional Carrier Calculus (⅔ Trap)

Master Autosomal & Sex-Linked Pedigree Probability Trees & Conditional Carrier Calculus (⅔ Trap) on the ESAT Biology paper. Traditional classroom derivations waste valuable seconds. Using the 2-step Sub-90 invariant elimination method compresses solve time to 45s, saving +115s per question.

Standard Classroom Time
160s
Textbook multi-line derivations bleed exam clock
Sub-90 Target Pace
45s
Comfortably below the 88.8s per-question limit
Time Saved for Review
+115s
Banks clock buffer across 27 questions

2-Step Sub-90 Shortcut Formula

How to eliminate intermediate algebra and solve under 45 seconds.

Launch Interactive Lesson
STEP 1 • SETUP INVARIANT (LINE 1)10–15s
Line 1 (Obligate Carrier Parents): Unaffected parents + ffff child   ⟹  I-1=Ff, I-2=Ff\implies \text{I-1} = Ff,\,\text{I-2} = Ff.

Establish the structural invariant and eliminate impossible options immediately.

STEP 2 • FAST SOLVE (LINE 2)15–25s
Line 2 (Condition on Unaffected): Cross out ffff from {FF,Ff,fF,ff}  ⟹  P(Ff∣unaffected)=23\{FF, Ff, fF, ff\} \implies P(Ff \mid \text{unaffected}) = \frac{2}{3} (20s).

Evaluate the simplified expression using integer factoring or unit elimination.

Distractor Trap Forensics

The predictable cognitive traps engineered by examiners into the wrong options.

TRAP #1fence_post_or_domain_trap

Using P(carrier) = 1/2 (2/4) instead of 2/3 for an UNAFFECTED sibling of an autosomal recessive sufferer (from Aa x Aa parents)

Since the sibling is phenotypically unaffected, the aa (1/4) genotype is already excluded, leaving 2 Aa carriers out of {AA, Aa, aA} = 2/3!

Sub-90 Fix: Test invariants before expanding equations.
TRAP #2factor_of_two_or_stoichiometry_trap

Forgetting to multiply by 1/2 when the question asks for the probability of an affected SON (or DAUGHTER) specifically

Omitting P(male) = 1/2 when the stem specifies the sex of the child rather than 'given that the child is a boy'.

Sub-90 Fix: Test invariants before expanding equations.
TRAP #3multi_statement_linchpin_foil

Failing to rule out X-linked recessive inheritance when an unaffected father has an affected daughter

An affected X-linked recessive female (Xʳ Xʳ) MUST inherit one Xʳ from her father, so her father MUST be affected (Xʳ Y).

Sub-90 Fix: Test invariants before expanding equations.

Try 1 Timed Question: Autosomal & Sex-Linked Pedigree Probability Trees & Conditional Carrier Calculus (⅔ Trap)

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Full Lesson All 15 Questions (ARCH-B-04)
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ARCH-B-04: Autosomal & Sex-Linked Pedigree Probability Trees & Conditional Carrier Calculus (⅔ Trap) (Sample)Biology
00:00.0
SUB-90 ZONE (<45S)
0.0s45s Sub-9090s ESAT Budget150s Classroom
Question 1 of 1ARCH-B-04 (6-Card Lesson)Format: Standard 5-Option
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Question 1 of 1 • 90s Target

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