What is Genetic Inheritance?
Genetic inheritance is how traits pass from parents to offspring through genes carried on chromosomes. Gregor Mendel's pea plant experiments revealed the basic rules — dominant and recessive alleles — that still explain how traits like eye color or blood type are inherited.
Genetic inheritance is the transmission of alleles from parents to offspring; each parent contributes one allele per gene, and dominant alleles mask recessive ones in the resulting phenotype.
- •Represented by a capital letter (e.g., T)
- •Masks the recessive allele's effect
- •Expressed if present in just one copy (Tt or TT)
- •Example: brown eyes in humans
- •Represented by a lowercase letter (e.g., t)
- •Effect is hidden when paired with a dominant allele
- •Only expressed when present in two copies (tt)
- •Example: blue eyes in humans
Step-by-step worked examples
Two heterozygous pea plants (Tt × Tt) are crossed for stem height, where T (tall) is dominant. What fraction of offspring will be tall?
Genotype ratio from Tt × Tt = 1 TT : 2 Tt : 1 tt TT and Tt are both tall (dominant allele present) 3 out of 4 offspring carry a T allele Fraction tall = 3/4 = 75%
A man with blood type AB (IAIB) and a woman with blood type O (ii) have children. What blood types are possible?
Father's gametes: IA or IB Mother's gametes: only i Possible offspring genotypes: IAi or IBi Offspring will be type A or type B, each with 50% probability
In humans, brown eyes (B) are dominant over blue eyes (b). Two Bb parents have 4 children. Statistically, how many are expected to have blue eyes?
Bb × Bb cross → 1 BB : 2 Bb : 1 bb Probability of bb (blue eyes) = 1/4 4 children × 1/4 = 1 Expected: 1 out of 4 children with blue eyes
Flashcards
Quick quiz
Q1.In a Tt × Tt cross, what genotype ratio results?
Q2.Which allele is expressed only when present in two copies?
Q3.What tool predicts offspring genotype ratios from a cross?
Q4.A tall pea plant (TT) is crossed with a short one (tt). What is the offspring's genotype?
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Common mistakes
Assuming a dominant trait is always the more common one. — Correct: Dominance means it masks the recessive trait when paired — it has nothing to do with frequency in a population.
Thinking genotype and phenotype are the same thing. — Correct: Genotype is the allele combination (e.g., Tt); phenotype is the visible trait it produces (e.g., tall).
Believing blending happens (e.g., Tt looks 'medium'). — Correct: With complete dominance, Tt looks exactly like TT — no blending occurs.
Forgetting that each parent contributes only one allele per gene. — Correct: Gametes are haploid, so each parent passes on exactly one of their two alleles per gene.
FAQ
What is genetic inheritance?
Genetic inheritance is how alleles for traits are passed from parents to offspring, following patterns first described by Gregor Mendel.
What is the formula for predicting inheritance ratios?
There's no single formula — a Punnett square is used to cross alleles (e.g., Tt × Tt) and predict a 3:1 phenotype ratio for a simple dominant/recessive trait.
What are examples of genetic inheritance?
Eye color, blood type, and pea plant height (Mendel's classic experiment) are all examples of genetic inheritance.
How do you calculate genetic inheritance probabilities?
Build a Punnett square with the parents' alleles on each axis, fill in every combination, then count the fraction of squares matching the trait you want.