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Genetics:
The study of heredity
Heredity = the passing of traits
from parents to offspring
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?
Trait = a feature or characteristic of
a person
 Physical appearance
ex: Hair Color
 Genetics:
 Environment:
hair color
hair texture
eye color
face shape
smile shape
Trait = a feature or characteristic of
a person
 Physical appearance
ex: Hair Color
 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
ex: Hair Color
 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
ex: Handedness
 Genetics:
 Environment:
Trait = a feature or characteristic of
a person
 Behavior tendencies
ex: Handedness
 Genetics: genes determine the tendency to
use a certain hand
 Environment:
Trait = a feature or characteristic of
a person
 Behavior tendencies
ex: Handedness
 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
ex: Heart disease
 Genetics:
 Environment:
Trait = a feature or characteristic of
a person
 Predisposed to medical conditions
ex: Heart disease
 Genetics: genes determine a risk of heart
disease
 Environment:
Trait = a feature or characteristic of
a person
 Predisposed to medical conditions
ex: Heart disease
 Genetics: genes determine a risk of heart
disease
 Environment: lifestyle
choices (diet, exercise,
habits) can increase
or decrease 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 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.
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 =
homozygous/purebred
 2 dominant alleles = homozygous dominant
 Example: B and B
Genotype =
Phenotype =
Mom
Dad
B
B
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
homozygous/purebred
 2 dominant alleles = homozygous dominant
 Example: B and B
Genotype = BB
Phenotype =
Mom
Dad
B
B
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
homozygous/purebred
 2 dominant alleles = homozygous dominant
 Example: B and B
Mom
Genotype = BB
Phenotype = brown eyes
B
Child
Dad
B
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
homozygous/purebred
 2 recessive alleles =
Mom
Dad
b
b
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
homozygous/purebred
 2 recessive alleles = homozygous recessive
 Example: b and b
Genotype =
Phenotype =
Mom
Dad
b
b
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
homozygous/purebred
 2 recessive alleles = homozygous recessive
 Example: b and b
Genotype = bb
Phenotype =
Mom
Dad
b
b
Child
Genotype = a person’s
combination of alleles
 A person may inherit 2 of the same alleles =
homozygous/purebred
 2 recessive alleles = homozygous recessive
 Example: b and b
Genotype = bb
Phenotype = blue eyes
Mom
Dad
b
b
Child
Alleles = different versions of a
gene
 A person may inherit 2 different alleles =
heterozygous/hybrid
 Dominant allele masks recessive allele
 Example: B and b
Genotype =
Mom
Dad
B
b
Child
Phenotype =
-or-
Mom
Dad
b
B
Child
Alleles = different versions of a
gene
 A person may inherit 2 different alleles =
heterozygous/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 =
heterozygous/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
homozygous
dominant
homozygous
recessive
heterozygous
Phenotype
Practice
 Brown hair (B) is dominant to blond hair (b).
Genotype
homozygous
dominant
homozygous
recessive
heterozygous
BB
Phenotype
Brown hair
Practice
 Brown hair (B) is dominant to blond hair (b).
Genotype
Phenotype
homozygous
dominant
BB
Brown hair
homozygous
recessive
bb
Blond hair
heterozygous
Practice
 Brown hair (B) is dominant to blond hair (b).
Genotype
Phenotype
homozygous
dominant
BB
Brown hair
homozygous
recessive
bb
Blond hair
heterozygous
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