Post on 13-Dec-2015
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
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?
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