Biology · Inheritance, variation and evolution. The idea in plain words, the rules to remember, the mistake to avoid and a worked example, written and checked by Mega Lecture.
Most genes have different forms called alleles. You inherit one allele of each gene from each parent, so you have two. The pair of alleles you have is your genotype. The characteristic that shows is your phenotype.
A dominant allele shows even if only one copy is present. A recessive allele shows only when both copies are recessive. A Punnett square lists the gametes of each parent and shows every possible combination in the offspring, so you can read off ratios and probabilities.
Sex is decided by one pair of chromosomes. Females are XX and males are XY.
A Punnett square gives probabilities, not promises. A 0.25 chance applies to every child separately, so it does not mean exactly one child in four will be affected.
Answer: 0.75 (75%).
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