Warm Up
1) A child is born with blue eyes even
though BOTH his parents have
brown eyes. How is this possible?
2) Can two blue eyed parents have a
brown eyed child? Explain why or
why not.
Genetics:
The study of heredity
Heredity = the passing of traits
from parents to offspring
The Incredibles
Heredity = the passing of traits
from parents to offspring
 Trait = A feature or characteristic of a
person
 Physical appearance
 Behavior tendencies
 Predisposed to medical conditions
 A person’s traits are influenced by:
 their genetic inheritance
 environmental factors
What is a trait?
Where are these traits
located?
 DNA!
 The DNA
“carries” the
traits that
make you who
you are!
Trait = a feature or characteristic of
a person
 Physical appearance
 Genetics:
 Environment:
hair color
hair texture
eye color
face shape
smile shape
Trait = a feature or characteristic of
a person
 Physical appearance
 Genetics: genes
determine natural
hair color
 Environment:
hair color
hair texture
eye color
face shape
smile shape
Trait = a feature or characteristic of
a person
 Physical appearance
 Genetics: genes
determine natural
hair color
 Environment: sun
or hair dyes change
hair color
hair color
hair texture
eye color
face shape
smile shape
Trait = a feature or characteristic of
a person
 Behavior tendencies
 Genetics:
 Environment:
Trait = a feature or characteristic of
a person
 Behavior tendencies
 Genetics: genes determine the tendency to
use a certain hand
 Environment:
Trait = a feature or characteristic of
a person
 Behavior tendencies
 Genetics: genes determine the tendency to
use a certain hand
 Environment:
can learn to use
the opposite
hand
Trait = a feature or characteristic of
a person
 Predisposed to medical conditions
 Genetics:
 Environment:
Trait = a feature or characteristic of
a person
 Predisposed to medical conditions
 Genetics: genes determine a risk of heart
disease
 Environment:
Trait = a feature or characteristic of
a person
 Predisposed to medical conditions
 Genetics: genes determine a risk of heart
disease
 Environment: eating
healthy foods and
exercising can reduce
risk
Trait = a feature or characteristic of
a person
 Phenotype = a person’s version of a trait
 “physical appearance”
hair color: black
hair texture: straight
eye color: blue
Practice
 List 3 genetic traits
Dash has.
 List Dash’s
phenotype for each
trait.
Trait = a feature or characteristic of
a person
 Gene = part of a person’s DNA that
influences a trait
Eye color gene
Face shape gene
Hair color gene
Gene = part of a person’s DNA
that controls a trait
 Alleles= different versions of a gene
Eye color gene:
brown allele
Eye color gene:
blue allele
Practice
 List 3 possible alleles for the hair color
gene.
Are there other
possibilities for
hair as well?
Hair color gene
Alleles = different versions of a
gene
 Dominant Allele
 Represented by a capital letter
 Example:
B for brown eyes
 Recessive allele
 Represented by a lowercase letter
 Example:
b for blue eyes
Alleles = different versions of a
gene
 All people have 2 alleles for every gene
(one from each parent)
Allele of
eye color
gene
from dad
Allele of
eye color
gene from
mom
Alleles = different versions of a
gene
 All people have 2 alleles for every gene
(one from each parent)
 Genotype = a person’s
combination of alleles
 “genetic makeup”
Allele of eye
color gene
from dad
Allele of eye
color gene
from mom
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 dominant alleles = purebred dominant
 Example: B and B
Genotype =
Phenotype =
Mom
Dad
E
E
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 dominant alleles = purebred dominant
 Example: B and B
Genotype = BB
Phenotype =
Mom
Dad
E
E
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 dominant alleles = purebred dominant
 Example: B and B
Mom
Genotype = BB
Phenotype = brown eyes
E
Child
Dad
E
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 recessive alleles =
Mom
Dad
e
e
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 recessive alleles = purebred recessive
 Example: b and b
Genotype =
Phenotype =
Mom
Dad
e
e
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 recessive alleles = purebred recessive
 Example: b and b
Genotype = bb
Phenotype =
Mom
Dad
e
e
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
purebred
 2 recessive alleles = purebred recessive
 Example: b and b
Genotype = bb
Phenotype = blue eyes
Mom
Dad
e
e
Child
Alleles = different versions of a
gene
 A person may inherit 2 different alleles =
hybrid
 Dominant allele masks recessive allele
 Example: B and b
Genotype =
Mom
Dad
E
e
Child
Phenotype =
-or-
Mom
Dad
e
E
Child
Alleles = different versions of a
gene
 A person may inherit 2 different alleles =
hybrid
 Dominant allele masks recessive allele
 Example: B and b
Genotype = Bb
Mom
Dad
E
e
Child
Phenotype =
-or-
Mom
Dad
e
E
Child
Alleles = different versions of a
gene
 A person may inherit 2 different alleles =
hybrid
 Dominant allele masks recessive allele
 Example: B and b
Genotype = Bb
Mom
Dad
E
e
Child
Phenotype = brown eyes
-or-
Mom
Dad
e
E
Child
Practice
 Brown hair (B) is dominant to blond hair (b).
Genotype
purebred
dominant
purebred
recessive
hybrid
Phenotype
Practice
 Brown hair (B) is dominant to blond hair (b).
Genotype
purebred
dominant
purebred
recessive
hybrid
BB
Phenotype
Brown hair
Practice
 Brown hair (B) is dominant to blonde hair (b).
Genotype
Phenotype
purebred
dominant
BB
Brown hair
purebred
recessive
bb
Blond hair
hybrid
Practice
 Brown hair (B) is dominant to blond hair (b).
Genotype
Phenotype
purebred
dominant
BB
Brown hair
purebred
recessive
bb
Blond hair
hybrid
Bb
Brown hair
Which genotypes are purebred? Which is hybrid?
Practice
 Right-handedness (R) is
dominant to left-handedness (r).
What genotype(s) could a right-handed
person have?
RR or Rr
What genotype(s) could a left-handed
person have?
rr
Practice
 In pea plants, green peas (G) are
dominant to yellow peas (g).
What would be the genotype of a:
-purebred green pea? GG
-hybrid green pea? Gg
-yellow pea? gg
Hands on Practice:
 Make sure you have a Punnet square
worksheet
 Step 1: Identify the parent genotypes
 Homozygous (2 of the same) dominant –
RED – capital R
 Homozygous recessive – WHITE – lower
case r
Hands on Practice
 Step 2 – place the
parents genotypes
in place to be
crossed
 R = red
 r = white
Hands on Practice
 Step 3 – combine
the genotypes for
each box
 R = red
 r = white
Hands on Practice
 Step 4 – write the
Write out the
genotypes and
phenotypes for all
offspring
Hands on Practice
Genotypes: 25% homozygous dominant
(RR), 50% heterozygous (Rr),
25% homozygous recessive (rr)
Phenotypes: 75% Red flowers and 25%
white flowers
Hands on Practice
Check point question: Could you ever have
pink flowers?