Download 3.1 Dominant, Recessive, Heterozygous

Dominant, Recessive, Heterozygous,
Homozygous
Catalyst:
Cedric has a deep voice.
1.


Is this genotype or phenotype?
HOW DO YOU KNOW?
Paula has one allele for
being tall, and one allele
for being short.
2.


Write in complete sentences!
Don’t talk during the Catalyst!
HW ON DESK!
Is this genotype or phenotype?
MASTERY TRACKER IN FOLDER!
HOW DO YOU KNOW?
Objectives

By the end of today, all SWBAT…
 Differentiate
between homozygous and
heterozygous genotypes
 Determine the phenotype of an organism,
based on its genotype
Agenda
Genotype and phenotype review
 Principal of Dominance
 Abbreviating Genotypes and Phenotypes
 Practice
 Exit Question

Remember yesterday?

Genes: Pieces of DNA you inherit from parents.

Alleles: Different versions of genes.

Genotype
 Combination
of alleles inherited from parents
 In your GENES

Phenotype
 PHYSICAL
showing of your genes
“Principle of Dominance”

Key Point #1: Dominant alleles mask
recessive alleles.
 Dominant
alleles make it like the recessive
allele isn’t there.
2
dominant alleles = dominant phenotype
 2 recessive alleles = recessive phenotype
 1 of each = dominant phenotype
Principle of Dominance example

GENE: Hair color
Dominant: Brown
 Alex
Recessive: Blonde
has two dominant alleles. His hair is
brown.
 Katlyn has two recessive alleles. Her hair
color is blonde.
 Amber has one dominant allele and one
recessive allele. Her hair is BROWN!!!
Check for Understanding (CFU)

Long fingers are dominant, short fingers are
recessive.
 Asia
has two dominant alleles.
 What type of fingers does she have?
Check for Understanding (CFU)

Long fingers are dominant, short fingers are
recessive.
 Tonya
has one dominant allele and one recessive allele.
 What type of fingers does she have?
Check for Understanding (CFU)

Long fingers are dominant, short fingers are
recessive.
 Brice
has two recessive alleles.
 What type of fingers does he have?
Check for Understanding (CFU)

Long fingers are dominant, short fingers are
recessive.
 Jaron
has one dominant allele and one recessive allele.
 What type of fingers does he have?
But Ms. S, I’m Lazy!

Key Point #2: There are three rules for
abbreviating genotype
1.
2.
3.

Dominant allele = CAPITAL letter
Recessive allele = lowercase letter
BOTH alleles use the same letter
Example: 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
One
dominant,
onedominant
recessive =
=
Both
recessive
Heterozygous
Homozygous
recessive
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
Check for Understanding (CFU)

Hair can either be straight (S) or curly (s). Caleb has
two alleles for curly hair.
 What
is his genotype in letters?
 ss
 What
is his genotype in words?
homozygous recessive
 What is his phenotype?
curly hair
Check for Understanding (CFU)

Forearms can either be hairy (H) or not hairy (h).
Zach has two alleles for hairy forearms.
 What
is his genotype in letters?
 HH
 What
is his genotype in words?
 Homozygous
 What
dominant
is his phenotype?
 Hairy
arms – gross!
Check for Understanding (CFU)

Lynda has one allele for straight hair, and one
allele for wavy hair. Straight hair is dominant over
wavy hair.
 What
is her genotype in letters?
 What is her genotype in words?
 What is her phenotype?
Whiteboard Practice!
Get it!
Got it?
GOOD!
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 is the 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 is the 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)


Front of worksheet. (COMPLETE SENTENCES!)
Back of worksheet is homework.
(Does not have to be in complete sentences – but
the assignment has to be complete for credit.)
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
genotype
1.
2.
3.
Dominant allele = capital letter
Recessive allele = lowercase letter
BOTH alleles use the same letter
Exit Question

Write in complete sentences!
Don’t talk during the 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.