Stnd 3 a Objective CNotes Punnett Square 011714

Stnd: 3 a Objective: C-Notes: Punnett Square 01/17/14 SWBAT: predict possible outcomes of phenotypes in a genetic cross from genotypes.

Why are Punnet Squares used? • To show all of the possible combinations of alleles from the parents • You can predict the genotypes and phenotypes of offspring if you know the genotypes of the parents

How to solve Punnet Square? 1. Determine the genotypes (letters) of the parents. Bb x Bb 2. Set up the Punnet square with one parent on each side. 3. Fill out the Punnet square middle 4. Analyze the number of offspring of each type In pea plants, round seeds are dominant to wrinkled. The genotypes and phenotypes are: RR = Round Rr = Round rr = wrinkled

Example In radishes, a bent root is a dominant trait, though some roots are straight (which is recessive). If a straight rooted plant is crossed with a heterozyous bent root plant, how many of the offspring will have straight roots? Step 1: Assign genotypes and phenotypes Step 2: Assign letters to represent the dominant trait Step 3: Make a key Step 4:

First Generation Punnett

As you can see, all of the offspring in Mendel’s first cross had a genotype of Pp. That’s why all of the plants in the first generation had purple flowers.

1 st 2 nd Generation First Generation Second Generation

Probability • When you flip a coin, there is a 50 percent chance you’ll get heads and a 50 percent chance you’ll get tails. • The way the coin lands is completely random. • Like flipping a coin, the chance of inheriting a certain genotype and phenotype is random.

IV. PUNNETT SQUARE 1. Tells the probability the offspring will have a particular trait 2. Example T = Tongue roller t = Can’t roll tongue * tongue rolling is dominant

Parents TT (parent 1) X tt (parent 2)

T t Parent 2 t Parent 1 T

T t Parent 2 t Tt Parent 1 T

T t Parent 2 t Tt Parent 1 T Tt

T t Tt Parent 2 Parent 1 T Tt

T Parent 1 T t Tt Tt Parent 2

Now you try it! B = brown eyes b = blue eyes * brown is dominant to blue

Parents Bb (parent 1) X Bb (parent 2)

B B Parent 2 b Parent 1 b

B B Parent 2 b BB Parent 1 b

B B Parent 2 b BB Parent 1 b Bb

B B BB b Bb Parent 2 Parent 1 b Bb

B Parent 1 b B BB Bb bb Parent 2

Genotype BB Bb bb Fraction 1/4 1/2 1/4 Percent 25% 50% 25% Ratio 1: 2: 1 Phenotype Fraction Percent Ratio brown eyes 3/4 75% 3: 1 blue eyes 1/4 25%

Practice Problem Yellow seeds are dominant to green seeds. Cross a heterozygous yellow seed and a homozygous green seed. What percent of the offspring will be yellow?