Nimo

Study smarter with Nimo

Personalised revision that adapts to you. Ace your revision with unlimited practice questions that are designed to help you learn faster. We're slowly rolling out to more and more students.

Try Nimo

Predicting outcomes with genetic crosses and probability

Inheritance, variation and evolution • Reproduction

Key concepts

What you'll likely be quizzed about

  • Probability indicates the chance of a particular genotype or phenotype resulting from a genetic cross.
  • Probabilities can be expressed as percentages, fractions, or ratios (for example, 1/4, 25%, or 1:3).
  • Each offspring represents an independent event; hence, probabilities apply to each offspring rather than a sequence of previous children.
  • The analogy of a coin toss illustrates this concept: the 50% chance of inheriting an allele from one parent remains 50% for every independent offspring.

Flashcards

Test your knowledge with interactive flashcards

Predict the genotype ratio from Bb × Bb.

Click to reveal answer

The expected genotypic ratio is 1 BB : 2 Bb : 1 bb (one homozygous dominant, two heterozygous, one homozygous recessive per four offspring).

Key notes

Important points to keep in mind

Alleles use letters: dominant capital, recessive lowercase.

Punnett squares display possible offspring genotypes from gamete combinations.

Probabilities apply individually to each offspring, independent of previous outcomes.

Express outcomes as fractions, percentages, or ratios for clarity.

Family trees utilize squares (for males), circles (for females), and shading to identify affected individuals.

Two unaffected parents with an affected child indicate recessive inheritance likely exists.

Punnett squares assume single-gene inheritance under random mating; many traits are polygenic.

X-linked traits generally exhibit greater male expression due to a single X chromosome.

Convert grid counts to proportions by dividing by total grid cells, typically four for single-gene crosses.

Mendel’s ratios arise from repeated crosses and counting significant numbers of offspring.

Built with v0