Wednesday – September 23, 2009

Objectives: SWBAT create and analyze Punnett

Squares.

Catalyst: What is the difference between a

gene and an allele? How do we represent dominant

alleles? Recessive alleles?

Agenda

Catalyst Review Making Babies Lab (GASP!) Punnett Squares Guided Practice Independent Practice Closing

Catalyst

A gene codes for a trait- eye color, ear lobes, dimples, etc.

An allele is a different version of a gene. Ex: Brown vs. Blue eyes Ex: Attached vs. Free hanging earlobes Ex: Dimples vs. No dimples

Review Yesterday’s Vocab

Traits Allele Homozygous Heterozygous Dominant Recessive

Check your

awesome notes!

Remember…

GENOTYPE = combination of alleles inherited from the parents (the genes)

PHENOTYPE = physical expression of the trait

Today, you are going to have 20 kids. What? Yes. In 15 minutes, you will have 20 kids. You will need to find someone in the

class to mate with. We will demonstrate how this works.

Key Point #1

Punnett Squares are diagrams that are used to predict the genotypes of offspring.

Probability…not EXACT

It is important to note that Punnett Squares only give probabilities for genotypes

It doesn’t give you the EXACT outcomes You will see when we start creating our Punnett Squares

Key Point #2

You can never know for sure what offspring will look like, you can only predict based on probability.

Key Point #3

We refer to the parent generation as P1 and the offspring of that generation as F1.

P1

F1

Before we get started…

CAPTIALIZED letters are DOMINANT lowercase letters are recessiveExamples: B = brown hair (DOMINANT)b = blonde hair (recessive)Y = yellow (DOMINANT)y = green (recessive) P = purple (DOMINANT)p = white (recessive)

Before we get started…

D = dimples

d = no dimples

D = dimples

d = no dimples

Homozygous dominant

Genotype: DD

Phenotype: have dimples

Homozygous dominant

Genotype: DD

Phenotype: have dimples

Homozygous recessive

Genotype: dd

Phenotype: no dimples

Homozygous recessive

Genotype: dd

Phenotype: no dimples

Heterozygous

Genotype: Dd

Phenotype: have dimples

Heterozygous

Genotype: Dd

Phenotype: have dimples

Before we get started…

B = brown eyes

b = blue eyes

B = brown eyes

b = blue eyes

Homozygous dominant

Genotype: BB

Phenotype: brown eyes

Homozygous dominant

Genotype: BB

Phenotype: brown eyes

Homozygous recessive

Genotype: bb

Phenotype: blue eyes

Homozygous recessive

Genotype: bb

Phenotype: blue eyes

Heterozygous Genotype: Bb

Phenotype: brown eyes

Heterozygous Genotype: Bb

Phenotype: brown eyes

Big Pun-nett

Let’s make our own. First things first, draw yourself box and split it into 4 squares.

Punnett like its Hot

Now, read the problem and find the parents’ genotypes.

*Remember, use the first letter of the dominant trait.

A homozygous dominant brown eyed male mates with a blue eyed female.

BB

bb

Punnett Squares are COOL

Parents go on the top and on the left (keep them together)

It doesn’t matter which parents goes on the top or the left B B

bb b

b

Punnett Square Dance

Now, bring em together. The four boxes represent the possible

kids.B B

b

b

Bb Bb

Bb Bb

Just Punnett!

Now, we analyze. Use quarters to figure out percentages.

B B

b

b

Bb Bb

Bb Bb

•How many homozygous dominant do we have? 0%

•How many heterozygous do we have? 100%

•How many homozygous recessive do we have? 0%

Punnett baby one more time Lastly, figure out percentages by

phenotypes.

B B

b

b

Bb Bb

Bb Bb

•What percentage will have brown eyes? 100%

•What percentage will have blue eyes? 0%

Let’s do one more on the board A heterozygous dimpled male mates

with a heterozygous dimpled female.

Whiteboard Guided Practice: Seed Shape

Solve the following Punnett Square.

A homozygous dominant round seeded plant is crossed with a heterozygous wrinkled plant.

Find the genotype and phenotype probabilities.R = round

r = wrinkled

RrRr

RRRRR

R

r

R

Guided Practice: Earlobes

Solve the following Punnett Square

A male with attached earlobes mates with a heterozygous free hanging earlobe female.

Find the genotype and phenotype percentages.

F = free

f = attached

ffFf

ffFff

F

f

f

Oh, how we love Spongebob! Your teacher will now pass out the

GP & IP “Punnett Squares – Spongebob Style” worksheets

We’ll do some of them together…then you get to try the rest on your own!

Wrap Up

Punnett Squares are diagrams that are used to predict the genotypes of offspring.

You can never know for sure what offspring will look like, you can only predict based on probability.

We refer to the parent generation as P1 and the offspring of that generation as F1.

Exit Question

Create a Punnett Square. Do a cross of

two heterozyous parents for brown

eyes. List the genotypes & phenotypes

probabilities of both the P1 and F1 generations.

Create a Punnett Square. Do a cross of

two heterozyous parents for brown

eyes. List the genotypes & phenotypes

probabilities of both the P1 and F1 generations.