Chapter 4 Probability and Heredity Section 2 Principles

Chapter 4 Probability and Heredity Section 2

Principles of Probability: the number that describes how likely it is that an event will occur Coin toss: two possible ways that the coin will land (heads up or tails up) 1 The in 2 chance, ½, 50% Laws of Probability predict what is LIKELY to occur

Independence of Events When you toss a coin more than once, the results of one toss do not affect the results of the next toss

Principles of Probability with Genetics Mendel realized that the mathematical principles of probability applied to his work He could say that the probability of producing… A tall plant was 3 in 4 A short plant was 1 in 4 HOW? !

Something called…. PUNNETT SQUARES Punnett square: a chart that shows all the possible combinations of alleles that result from a genetic cross They show all the possible outcomes of a genetic cross and determine the probability of that outcome

Example Hybrid (one dominant, one recessive) R: round seed (dominant) r: wrinkled seed (recessive) R r RR Rr Rr rr

Using a Punnett Square Use a Punnett square to calculate the probability In a genetic cross, the allele that each parent will pass on to its offspring is based on probability

What is the probability that the offspring will be RR? What is the probability that the offspring will be rr? 50% or 2 in 4 What is the probability that the offspring will be a round seed? 25% or 1 in 4 What is the probability that the offspring will be Rr? 25% or 1 in 4 75% or 3 in 4 What is the probability that the offspring will be a wrinkled seed? 25% or 1 in 4

Predicting Probabilities Dominant: black fur Recessive: white fur What are the possible allele combinations? Bb What is the probability the guinea pig has black fur? 100%

Phenotypes and Genotypes Phenotype: physical appearance, or Genotype: genetic makeup, or allele What Smooth pods What is the dominant trait? is the recessive trait? Pinched How many different phenotypes? How many different genotypes? visible traits combination

Homozygous and Heterozygous Purebred SS or ss Hybrid Ss = two identical alleles = homozygous = two different alleles = heterozygous

Codominance Codominance: the alleles are neither dominant nor recessive Both results are expressed in the offspring, black and white feathers Will the offspring be heterozygous? Or homozygous?