Probability

Definition: Probability is the likelihood or chance that a specific event will occur.
Example: Tossing a coin—there is a 50% chance (1/2) that it will land on heads and a 50% chance (1/2) that it will land on tails.
Law of Large Numbers: The more times an event occurs, the closer the actual results match the expected probability.

The rules of probability apply to genetic inheritance, particularly during gamete formation and fertilization.
Each meiosis event and fertilization act like a coin toss, with each allele having an equal chance of being passed on.

Example: A plant with genotype Pp for flower color.
During meiosis, the two alleles segregate, meaning:
- 50% of gametes get the P allele.
- 50% of gametes get the p allele.
This follows Mendel’s Law of Segregation—each gamete randomly receives one allele from each parent.

If both parents have the genotype Pp, each parent’s gametes combine randomly.
The chance of each possible combination:
- PP (homozygous dominant) → 25% (1/4)
- Pp (heterozygous) → 50% (2/4)
- pp (homozygous recessive) → 25% (1/4)
These probabilities are visualized using a Punnett square.

Define probability. Apply the term to a coin toss.
- Probability is the chance of an event occurring. In a coin toss, the probability of landing on heads is 50%.
How is gamete formation like tossing a coin?
- Each allele has an equal chance (50%) of being passed to a gamete, just like each side of a coin has a 50% chance of landing face-up.
With a PP homozygote, what is the chance of a gamete having the P allele? The p allele?
- 100% of gametes will have the P allele because both copies of the gene are dominant (PP).
- 0% chance of a gamete having the p allele since it is not present in the parent’s genotype.