1 Review What is probability Use Models How are Punnett squares used to predict

the outcomes of genetic crosses2 Review What is independent assortment Calculate An F1 plant that is homozygous for shortness

is crossed with a heterozygous F1 plan. What is the probability that a seed from the cross will be tall. Use a Punnett Square to explain your answer and to compare the probable genetic variations in the F2 plants

3 Review How did Gregor Mendel contribute to our understanding of inherited traits

Apply Concepts Why is the fruit fly an ideal organism for genetic research

CH 11 INTRODUCTION TO GENETICS11.2 Applying Mendel’s Principles

Probability Math prediction as to chances of something

happening Chance of passing on a particular gene Coin has two sides, a head and a tail, if you flip it, the

chance of getting a head is ½.

If you flip a coin three times in a row, what is the probability that it will land heads up every time

Each flip is and independent event with a chance of ½

1/2 × 1/2 × 1/2 = 1/8.

F1 plant had one tall allele and one short allele (Tt)

1/2 of the gametes would carry the short allele (t).

The only way to produce a short (tt) plant is for two gametes carrying the t allele.

Chance of getting t allele is ½

Probability of being short (tt) is

½ x ½ = ¼.

For each of Mendel’s seven crosses, about ¾ of the plants showed the trait controlled by the dominant allele

¼ showed the recessive trait.

Probabilities predict the average outcome The larger the sample the closer to the predicted.

Homozygous Two of the same alleles TT or tt

Heterozygous One of each version of the alleles, Hybrid Tt.

Genotype What the actual genes are, you can’t physically see TT, Tt, or tt

Phenotype What the trait looks like, what you can physically see Tall or short.

Punnett Squares

Genetic cross to predict the genotype and phenotype using mathematical probability

Monohybrid One trait cross

Dihybrid Two trait cross.

How To Make a Punnett Square

1. Start with the Parents2. Figure out the Gametes3. Line them up4. Fill in the Punnett Square5. Figure out the Results.

Start with the Parents

Write the genotypes of the two parents

Bb and Bb.

Figure out the Gametes

Determine what alleles would be found in all of the possible gametes that each parent could produce.

Line them up

Draw a table with enough spaces for each pair of gametes from each parent

Enter the genotypes of the gametes produced by both parents on the top and left sides of the table.

Fill in the Punnett Square

Fill in the table by combining the gametes’ genotypes.

Figure out the Results

Determine the genotypes and phenotypes of each offspring

Calculate the percentage for each.

Homozygous round x Homozygous wrinkled

Homozygous round x Homozygous wrinkled

R

R

r

r

Homozygous round x Homozygous wrinkled

R

R

r Rr Rr

r Rr Rr

Homozygous round x Homozygous wrinkled

R

R

r Round Round

r Round Round

Independent Assortment

Genes for different traits can segregate independently during gamete formation

A past coin flip won’t influence a future coin flip.

Mendel crossed true-breeding round yellow peas with wrinkled green peas.

Round yellow peas had the genotype RRYY, which is homozygous dominant.

Wrinkled green peas had the genotype rryy, which is homozygous recessive.

All of the F1 offspring produced round yellow peas

F1 offspring was RrYy, heterozygous for both seed shape and seed color.

Mendel then crossed the F1 plants to produce F2 offspring.

Alleles for seed shape segregated independently of those for seed color

Mendel’s experimental results were very close to the 9:3:3:1 ratio that the Punnett square shown predicts.

Start with Parents

Figure out the Gametes

Line them Up

Fill in the Punnett Square

Figure out the Results

Thomas Hunt Morgan

Repeated Mendel’s work using fruit flies.