Punnett Square / Inheritance Patterns

Case-based practice for recognizing autosomal, X-linked, and special inheritance

Interactive Practice

Inheritance Pattern Reference Study Guide

Pattern	Key Clues	Example Traits	Genotype Notation
Autosomal Recessive	May skip generations; both parents unaffected carriers; equal sex distribution	Cystic fibrosis, PKU, Tay–Sachs	`Aa × Aa` `Aa × aa`
Autosomal Dominant	Present in successive generations; affected parent → ~50% of offspring; equal sex distribution	Huntington disease, Marfan syndrome	`Aa × aa` `Aa × Aa`
X-linked Recessive	More males affected; carrier mothers; affected father → carrier daughters, no affected sons unless mother is carrier	Hemophilia A, Duchenne MD	`X^HX^h × X^HY`
X-linked Dominant	Affected father → all daughters affected, no sons; affected mother → ~50% of both sexes	Rett syndrome	`X^AX^a × X^aY`
Incomplete Dominance	Heterozygote shows blended/intermediate phenotype between the two homozygotes	Snapdragon flower color	`RR` red · `Rr` pink · `rr` white
Codominance	Both alleles fully expressed in heterozygote; no blending	ABO blood group	`I^Ai × I^Bi`
Mitochondrial	Maternal transmission only; all children of affected mother are affected; fathers do not transmit	LHON	Maternal `H` passed to all offspring

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Possible Carrier Affected Unaffected

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Genotype	Count / %	Phenotype	Result
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— Pattern Identified

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