Unit 5 · 5.4 — Non-Mendelian Genetics [cite: 9, 10]

Everything to learn here

• Concept: Many biological traits deviate significantly from predicted Mendelian ratios due to complex mechanisms like sex-linkage, linked genes, incomplete dominance, codominance, or polygenic inheritance [cite: 10, 13, 14].
• Concept: Genes located very closely together on the same physical chromosome tend to be inherited together as a unit (linked genes), violating Mendel's law of independent assortment [cite: 14].
• Vocabulary: Sex-Linked Trait — a phenotypic trait heavily controlled by a gene located on a sex chromosome (overwhelmingly the X chromosome in humans) [cite: 13, 14].
• Vocabulary: Incomplete Dominance — a scenario where the heterozygous phenotype represents a perfect intermediate blend of the two distinct homozygous phenotypes [cite: 14].
• Vocabulary: Polygenic Inheritance — an additive effect of two or more separate genes on a single phenotypic character, resulting in a spectrum of continuous variation (e.g., skin color, height) [cite: 13, 14].
• Equation: Equation/Process: Chi-Square Statistical Test: $\chi^2 = \Sigma \frac{(O - E)^2}{E}$ where degrees of freedom $df = \text{categories} - 1$ [cite: 31].
• Skill: FRQ Task Verb "Evaluate" — Use the Chi-Square statistical test to evaluate whether observed laboratory genetic ratios differ significantly from mathematically expected Mendelian ratios, rejecting or failing to reject the null hypothesis [cite: 19, 31, 41].
• Concept: Sex-linked traits are carried on sex chromosomes and often show different inheritance frequencies between males and females.
• Vocabulary: Pleiotropy — A genetic scenario where one single gene exerts influence over multiple, distinct phenotypic characteristics.
• Concept: Traits found in mitochondrial or chloroplast DNA are typically inherited maternally because these organelles are provided by the egg.

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