Inheritance Patterns and
Human Genetics
Sex Chromosomes and Autosomes
• Sex Chromosomes
contain genes that
determine the gender
of an individual.
• Many organisms have
the XX & XY
chromosomal
mechanism to
determine the sex of
an individual.
Sex Chromosomes and Autosomes
• In certain organisms,
like chickens and
moths, males have
two identical
chromosomes and
females have two
different
chromosomes.
Sex Determination
• In mammals, the male
determines the sex of
the offspring.
• If the sperm
contributes an X sex
chromosome, a
female will be created
• If the sperm
contributes a Y sex
chromosome, a male
will be created.
The Y Chromosome
• In a male mammal,
the Y chromosome
contains a gene
called SRY (Sexdetermining Region
Y)
• This gene codes for a
protein that causes
gonads of an embryo
to develop as testes.
Sex
Linkage
• Genes found on
the X
chromosome are
said to be X-linked
• Genes found on
the Y
chromosome are
said to be y-linked
Mutations
• Change in the nucleotide-base sequence of a
gene or DNA molecule
Mutations
• Germ-cell mutations
occur in an
organism’s gametes.
• These do not affect
the organism itself,
but can be passed on
to offspring.
Mutations
• Somatic-cell
mutations take place
in an organism’s body
cells.
• These mutations can
affect the organism
but are not passed on
to offspring
Mutations
• Lethal mutations cause death, often before
birth.
• Some mutations will produce a phenotype
that is beneficial to an organism.
• Mutations provide the variation upon which
natural selection acts.
Chromosome Mutation
Deletion
• Loss of a piece of a chromosome due to
breakage
Chromosome Mutation
Inversion
• A chromosomal segment breaks off, flips
around backward, and reattaches.
Chromosome Mutation
Translocation
• A piece of one chromosome breaks off and
reattaches to a nonhomologous chromosome
Chromosome Mutation
Nondisjunction
• A chromosome fails to separate from its
homologue during meiosis.
Gene Mutations
• The substitution,
addition, or removal
of a single
nucleotide is called
a Point Mutation
• This image shows
a substitution point
mutation.
Gene Mutation (Frameshift)
• If a nucleotide is
deleted (Deletion),
this can cause an
incorrect grouping of
the remaining codons.
This is called a
frameshift mutation.
Gene Mutation (Frameshift)
• If a nucleotide is inserted (insertion mutation), this
can cause an incorrect grouping of the remaining
codons. This is also called a frameshift mutation.
CTTCGAAGTC
CTATCGAAGTC
Inheritance of Traits
Pedigrees
• A diagram that shows how a trait is inherited
over several generations.
Can you make sense of this
Pedigree?
Polygenic Inheritance
• Most human traits are
polygenic.
• This means they are
influenced by several
genes.
• Often show many
degrees of variation.
• Eye color, height, hair
color and skin color.
Multiple Allele Inheritance
• Genes with three or
more alleles
• The ABO blood types
are controlled by 3
alleles.
• A, B, i
• A & B are dominant to i
Blood Types
Phenotypes
A
B
AB
O
Genotypes
AA, Ai
BB, Bi
AB
ii
Rh Factor for Blood
• Rh stands for Rhesus
Factor
• If you are Rh +, you
have a blood protein
that Rh – people do
not have.
• Rh+ is dominant to
Rh –
• 85% of the US
population is Rh+
Rh Factor Problems
• When a pregnant
woman who is Rh - is
having a Rh + baby
the woman will
produce antibodies
against the foreign
protein.
Rh Factor Problems
• The woman’s first child will not
be affected.
• If the woman has any other
children, her antibodies can
attack the babies blood
causing death to the baby.
• There are injections that are
given to women today to keep
this from being a problem.
X – Linked Traits
• Traits and disorders that are found on the
X chromosome
• For a man to have an X-linked disorder, he
only needs the trait on his one X.
• For a female to have an X-linked disorder,
she needs to have the trait on both of
them. (unless it is a dominant X-linked
trait)
X – Linked Traits
• Color blindness is a recessive X-linked
disorder
X – Linked Traits
• Hemophilia is also a
recessive X-linked
disorder
Sex-Influenced Traits
• The presence of male or
female sex hormones
influence the expression of
certain human traits
Disorders due to Nondisjunction
• Monosomy – when an
organism has only one copy
of a particular chromosome
• Trisomy – when an
organism has 3 copies of a
particular chromosome
Disorders due to Nondisjunction
•
•
•
•
Down Syndrome (trisomy 21)
Turner Syndrome (X0)
Klinefelter’s Syndrome (XXY)
Triple X Syndrome (XXX)
Genetic Screening
• Amniocentesis –
amniotic fluid is
removed and a
karyotype of the baby
is produced.
Genetic Screening
• Chorionic Villi Sampling
– a sample of the tissue
that grows between the
mother’s uterus and the
placenta is taken.
• A karyotype is
produced.