Dominant, Recessive, Heterozygous, Homozygous

Catalyst: Roy has a deep voice.

Is this genotype or phenotype? HOW DO YOU KNOW?

Khadijah has one allele for being tall, and one allele for being short. Is this genotype or phenotype? HOW DO YOU KNOW?

Write in complete sentences!

Don’t talk during the Catalyst!

Objectives

By the end of today, all SWBAT… Differentiate between homozygous

and heterozygous genotypes Determine the phenotype of an

organism, based on its genotype

Quick Review

All living organisms have two alleles for every gene Gene controls one trait Allele = version of a gene

Genotype = which alleles you got from parents

Phenotype = physical expression of the genotype

Principle of Dominance

The two types of alleles are dominant and recessive.

Key Point #1: If an organism is heterozygous, a dominant allele will mask the recessive allele. Example: hair color (gene)

The brown allele is dominant, the blonde allele is recessive

Brenna has two blonde alleles. Her hair color is blonde.

Wellington has two brown alleles. His hair is brown. JaQuia has one brown allele and one blonde allele.

Her hair is BROWN!!!

Check for Understanding (CFU) Long fingers is dominant, short fingers is

recessive Sabreen has two dominant alleles What type of fingers does she have?

Check for Understanding (CFU) Long fingers is dominant, short fingers is

recessive Joceyln has one dominant allele and one

recessive allele What type of fingers does she have?

Check for Understanding (CFU) Long fingers is dominant, short fingers is

recessive Jessica has two recessive alleles What type of fingers does he have?

Check for Understanding (CFU) Long fingers is dominant, short fingers is

recessive Wafa has one dominant allele and one

recessive allele What type of fingers does he have?

But Mr. J, I’m Lazy!

Let’s abbreviate things. Key Point #2: There are three rules

for abbreviating genotype1. Dominant allele = capital letter2. Recessive allele = lowercase letter3. BOTH alleles use the first letter of the

dominant trait Long tails in dogs are dominant, short

tails are recessive Long = L Short = l

Dominant and Recessive Genotypes For every gene you have two alleles, and

each of those could be dominant or recessive.

So a dog could have THREE different GENOTYPES for tail length: LL Ll ll

Both dominant = Homozygous

dominant

Both dominant = Homozygous

dominantBoth

recessive = Homozygous

recessive

Both recessive =

Homozygous recessive

One dominant,

one recessive =

Heterozygous

One dominant,

one recessive =

Heterozygous

Dominant and Recessive Phenotypes But dogs could only have two different

tail lengths. Remember that a dominant allele will

mask a recessive one. So for this genotype you get…. LL (long tail) Ll (long tail) ll (short tail)

Let’s Practice More

Pea plants can have two alleles for the gene for height: tall and short. Tall is dominant to short.What letters would represent the two alleles?What would be the genotype of a heterozygous flower?What would be the phenotype of a flower with TT?What would be the phenotype of a flower with Tt?

T, t

Tt

Tall

Tall

two types

WORD BANK: allele, dominant (3x), homozygous recessive, recessive (2x), homozygous dominant, heterozygous

two of this kind two of this kindone of each

looks looks looks

Whiteboard Practice!

Guided Practice

The bunnies of the forests of Louisiana can either be brown or black. Brown is dominant over black.

Write all the genotypes possible for a brown bunny.

Guided Practice

The bunnies of the forests of Louisiana can either be brown or black. Brown is dominant to black.

What is the genotype AND phenotype of a bunny that is heterozygous?

Guided Practice

The bunnies of the forests of Louisiana can either be brown or black. Brown is dominant to black.

What is the genotype AND phenotype of a bunny that is homozygous recessive?

Guided Practice

People can have either free or attached earlobes. Free is dominant over attached.

What letters would you use to represent EACH allele?

Guided Practice

People can have either free or attached earlobes. Free is dominant to attached.

What genotype AND phenotype of someone who is homozygous dominant?

Guided Practice

People can have either free or attached earlobes. Free is dominant to attached.

What genotype AND phenotype of someone who is heterozygous?

Guided Practice

Chickpeas can be either green or yellow. Yellow is dominant over green.

List all the possible genotypes for a yellow chickpea.

Guided Practice

Chickpeas can be either green or yellow. Yellow is dominant over green.

What is genotype AND phenotype of a chickpea that is homozygous recessive?

Guided Practice

Chickpeas can be either green or yellow. Yellow is dominant over green.

What is genotype AND phenotype of a chickpea that is heterozygous?

Independent Practice (IP)

Key Point Wrap-Up

Key Point #1: Dominant alleles mask recessive alleles. Homozygous dominant = dominant

phenotype Homozygous recessive = recessive

phenotype Heterozygous = dominant phenotype

Key Point #2: There are three rules for abbreviating genotype1. Dominant allele = capital letter2. Recessive allele = lowercase letter3.BOTH alleles use the same letter

Pre-test

Exit Question

The gene for fur color in mice has alleles for brown and white. Brown is dominant to white. What letters are used for the

alleles? Write the genotype AND

phenotype for a mouse that is homozygous recessive. Write in complete sentences!

Don’t talk during the Exit Question!