Monday 11/16/15 Learning Goal: Determine how probability helps explain the results of genetic crosses. Warm-up: What is codominance? Homework: Packet pages 8-10 TEST on FRIDAY Ch. 4 Sec. 1 & 2

Chapter 4 Probability and Heredity Section 2

Principles of Probability  Probability:  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 in 2 chance, ½, 50%  The 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 4HOW?!

Something called…. PUNNETT SQUARES  Punnett square:  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) RRrRr RrRrr Rr R r

Using a Punnett Square  Use a Punnett square to calculate the probability 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?  25% or 1 in 4  What is the probability that the offspring will be rr?  25% or 1 in 4  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?  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:  Dominant: black fur  Recessive:  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:  Phenotype: physical appearance, or visible traits  Genotype:  Genotype: genetic makeup, or allele combination  What is the dominant trait?  Smooth pods  What is the recessive trait?  Pinched  How many different phenotypes? How many different genotypes?

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

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?