Read Why Human Inheritance Uses Pedigrees
Human traits are studied through family records because experimental crosses are not possible.
Pedigree Analysis is the central idea in this question pattern. Identify the condition in the stem before applying the method below.
Use family histories
Researchers cannot control human matings, and families produce relatively few offspring. Pedigrees trace how traits appear across generations and support inheritance inference.
Distinguish pedigree patterns
Autosomal dominant traits often appear across generations and affect both sexes. Mitochondrial traits follow the maternal line: affected mothers may pass them to children of either sex, but affected fathers do not transmit mitochondrial DNA.
Use father-to-child transmission first
An affected father transmits his X chromosome to every daughter and no son. When all daughters are affected while sons are unaffected, with an unaffected outsider, the diagnostic pattern is X-linked dominant inheritance. Use this father-to-child rule before counting every affected person: choose C.
Rule out inheritance modes from a pedigree
Unaffected parents with affected son and daughter indicate recessive inheritance. An affected daughter with an unaffected father rules out X-linked recessive inheritance, leaving autosomal recessive. Choose B.
OlympIQ exam lens
- ✓No controlled crosses in humans.
- ✓Small progeny size limits direct ratio tests.
- ✓Pedigrees record traits across generations.
- ✓Autosomal dominant: vertical transmission in either sex.
- ✓Mitochondrial: maternal transmission only.
- ✓Affected father → all daughters and no sons indicates X-linked dominant inheritance.
- ✓An affected daughter with an unaffected father rules out X-linked recessive inheritance in this pattern.
A pedigree shows inheritance patterns; it does not make the family an experimental cross.
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