Chapter 4Probability and HereditySection 2

I can… explain the role of probability in a genetic cross Warm Up: If a mother rabbit is hybrid for

black fur, and black fur is dominant, how would you write her alleles?

Wrap Up: Draw a punnett square for the cross: Hh x Hh

Principles of 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 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)

RR Rr

Rr rr

R r

R

r

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? 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: 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 visible traits 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

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?