5.2 Life Science
Types of Dominance
 Incomplete Dominance – when the offspring of two
homozygous parents show an intermediate (mixed)
phenotype
 Like mixing of paint
 Example: Some horse breeds can produce a mixture of
traits. Chestnut x Carmelo = Palomino (pg. 134)
 Codominance – when the offspring of two
homozygous parents show an combinations
phenotype. Both traits are seen.
 Example: black chicken x white chicken = spotted
chicken
Multiple Alleles
 Many traits are controlled by more than two alleles.
 Traits controlled by multiple alleles produce more
than three phenotypes of that trait.
 Example: Blood Types
Blood Types
(Alleles)
Genotype
Blood Type
Type of
Dominance
IA IA or IA i
A
Dominant
IB IB or IB i
B
Dominant
IA IB
AB
Codominant
ii
O
Recessive
Polygenic Traits
 Eye color is an example of a trait that is produced by a
combination of many genes.
 Other Examples:
 Skin color, hair color, number of eggs a chicken
produces, the color of grain in wheat, etc…
 It is hard to classify polygenic traits
 The environment also plays an important role in the
expression of traits controlled by polygenic
inheritance.
Impact of the Environment
 Your environment plays an important role in the
expression of some of your genes.
 Can be internal or external factors.
 Example: the sizes of leaves –

Trees have certain sizes of leaves based on the type of species
it is. If the tree does not receive enough nutrients or water,
then the tree will not grow and develop as it should. Or it may
receive more than required and the tree does better than it’s
genes are designed to do. This is called Genetic Potential.
Mutations
 Mutations are errors in the genetic make-up of an
organisms
 Chromosomal or Gene mutations can occur
 Not all mutations are harmful
 May lead to adaptations within a population and then
evolution.
 Mutations occur during DNA replication and Cell
Division. They may also occur due to external exposure
to chemicals or x-rays.
 Example: Cancer
Chromosome Disorders
 Having an additional or missing a chromosome can
cause the individual to have the wrong number of
chromosomes.
 Nondisjunction may occur during meiosis or mitosis
 The failure for homologous chromosomes to separate
properly resulting in a mutation
 Crossing-over also occurs during meiosis or mitosis
 When a piece of a chromosome breaks off and
reattaches to a different chromosome or not at all.
Types of Genetic Disorders
 Downs Syndrome
 Chromosomal Disorder
 Extra Chromosome on
set 21 (XXX instead of
XX)
 Trisomy 21
 Can be shorter, exhibit
learning disabilities,
and may have heart
problems
Types of Genetic Disorders
 Cystic Fibrosis
 Homozygous Recessive Disorder
 A thick mucus is produced in the lining of the lungs and
digestive system
 Makes it hard to breath and can cause digestion
problems as well
 Physical therapy, special diets, and new medications and
drug therapies can help increase life span of patients.
Sex Determination
 Scientist have studied fruit flies because they only
have 4 large chromosomes, which make it easy to
study.
 One pair of certain genes are used to determine
gender.
 XX represent female and XY represents male
 Each egg produced normally contains one X
chromosome. Males produce sperm that normally
contains either an X or a Y chromosome.
Sex-Linked Disorder
 Some inherited conditions are linked to gender on the
X or Y chromosomes.
 An allele inherited on a sex chromosome is called a
sex-linked gene (trait).
 Color blindness is a sex-linked disorder
 Recessive allele carried on the X chromosome
 Because males have only one X chromosome, a male
with this allele on his X chromosome is color blind.
 However, a color blind female must have this allele on
both X chromosomes in order to exhibit the trait.
Color Blind Punnett Square
Sex-Linked Disorders
 Calico cats are recessive and carried on the X
chromosome as well.
 Two recessive alleles must be present for this allele to
be expressed in female cats
Pedigrees Trace Traits
 A pedigree is a visual tool for following a trait through
generations of a family.
 Males are represented by squares and females are
represented by circles.
 A completely filled in circle or square indicates that
trait is seen in that person.
 A half-colored square or circle indicates that the
person is a carrier.
 Heterozygous for the trait.
Pedigrees
Pedigrees
 A pedigree is useful tool for studying how traits in a
family is inherited over many generations.
 It can show if the trait is dominant, recessive, or sexlinked.
 Pedigrees are also used in breeding animals or plants
to possibly predict if the desirable traits will be present
in the offspring.
 Issues concerning health also are considered when
researching pedigrees.