Mutations and Pedigree Notes

What is a mutation?

• Mutation= any change in DNA (the order

of nucleotide bases/letters)
– Can occur in any cell in the body. Remember

from the cells unit that mutations can lead to
cancer (uncontrolled cell growth)

– Caused by:

• Mistakes made during DNA replication, mitosis,

meiosis, or protein synthesis

• Mutagens = chemicals that can cause DNA

mutations Ex. radiation, UV light, cigarette smoke

• Viruses

Multiple Choice

Normal-
GAG-CTC-GAC-AGA
Mutant
GAG CTC-CAC-AGA

• no mutation

• substitution

• insertion

• deletion

Multiple Choice

What is a genetic mutation

• the making of a zombie

• any change in the DNA base pairs

• the process of duplicating the DNA in a cell

Are mutations always bad?

Not necessarily!

Multiple Choice

Are all mutations bad?

• Yes

• No

There are 2 main types of mutations:

1. Gene mutations—happen during DNA

replication = A change to the original DNA
sequence

Ex. Cystic Fibrosis, Dwarfism, and Sickle Cell

Anemia

2. Chromosome mutations—happen during

meiosis = Changes the number or location of
genes

Ex. Down Syndrome, Klinefelter’s Syndrome,
Turner’s Syndrome

Gene Mutations

• Point mutations: substitute one

nucleotide for another
– ATTACC🡪 AATACC

• Frameshift mutations: the insertion or

deletion of a nucleotide
– ATTACC 🡪 ATACC (deletion)
– ATTACC 🡪 ACTTACC (insertion)
– These will affect all the codons that come

after the insertion or deletion

Chromosome

Mutations

• Duplication:changes the size

of chromosomes and results in
multiple copies of a single gene

• Translocation: pieces of

non-homologous chromosomes
exchange segments (during
crossing over)

• Nondisjunction:

Chromosomes do not separate
correctly during anaphase,
resulting in 1 or 3
chromosomes rather than 2 per
cell.

Nondisjunction

Multiple Choice

A substitution mutation occurs when

• a base pair is missing from the DNA strand

• a base pair is added to the DNA strand

• a base pair is replaced with a different base pair

Multiple Choice

An insertion/additon mutation occurs when

• a base pair is missing from the DNA strand

• a base pair is added to the DNA strand

• a base pair is replaced with a different base pair

Multiple Choice

A deletion mutation occurs when

• a base pair is missing from the DNA strand

• a base pair is added to the DNA strand

• a base pair is replaced with a different base pair

Down Syndrome

An example of nondisjunction 🡪 3 copies of chromosome 21

Types of Human Genetic

Disorders

• Autosomal Recessive Disorders
• Autosomal Dominant Disorders
• Sex-Linked Disorders
• Autosomal Chromosome

Disorders

• Sex Chromosome Disorders

Autosomal Recessive Disorders

• Caused by the presence

of 2 recessive alleleson
autosomes

– Carrier– does NOT show

disease, but can pass the
disease-causing allele to
offspring.

• Examples:

– Cystic fibrosis– affects the

sweat glands & mucus glands.

– PKU - lacks enzyme that is

needed to break down
phenylalanine, an amino acid in
milk and many other foods.

Ex. 2 carriers have a 25%

chance of having a child with the

disease.

Autosomal Dominant Disorders

• Caused by the presence of

at least 1 dominant allele
on autosomes

– Dominant genetic disorders

are less common than
recessive disorders.

• Why do you think that is?

• Examples:

– Achondroplasia (Dwarfism)
– Huntington’s disease– damages

the nervous system and usually
appears during adulthood.

At least one parent must have

the disease in order to pass it on

Still possible to have unaffected
children if one parent is hetero
and the other is homo. recessive

Sex-Linked Disorders

• Caused by the

presence of an allele
on the X sex
chromosome

• Examples:

- Colorblindness- found in 1 in

10 males and 1 in 100 females.

- Hemophilia- does not allow

normal blood clotting to occur

- Muscular dystrophy- results in

the progressive weakening and
loss of skeletal muscle

If mom is carrier and Dad is
normal, boys get the disease

instead of girls

Autosomal Chromosome

Disorders

• Often caused by

nondisjunction of autosomes
= the failure to separate
homologous chromosomes
during meiosis.
– Causes an abnormal number of

chromosomes due to a mistake
in meiosis

• Example:

– Down syndrome- most common

form of trisomy involving three
copies of chromosomes 21.

Sex Chromosome Disorders

• Often caused by

nondisjunction of sex
chromosomes
– Causes an abnormal number

of sex chromosomes due to
a mistake in meiosis

• Examples:

– Turner’s syndrome- inherit only

one X chromosome.

– Klinefelter’s syndrome- occurs in

males when an extra X
chromosome. Males can have
XXY, XXXY or XXXXY sex
chromosomes.

Pedigree

• Pedigree– chart used to trace the phenotypes and

genotypes in a family to determine whether people
carry diseases or traits

•Similar to a family tree, but it traces a trait or disease through the family
line

•Can be used by potential parents or genetic counselors to determine
the probability of passing on the disease to children.

•Studying pedigrees can help scientists determine the inheritance
pattern for a trait (dominant or recessive, sex-linked or autosomal)

Pedigree Notation

Male

Female

Married

Kids

I

II

III

Has it

Doesn’t have it

Autosomal Recessive

• Most common inheritance pattern for genetic

diseases

• Disease is rare in the family (only a few affected

family members)

• Males and femalesare equally likely to inherit this

disease

• Disease often skips generations(a child may

inherit the disease even though neither of the
parents have the disease.)

• Examples: Cystic Fibrosis, Sickle Cell Anemia,

Phenylketonuria (PKU), Tay-Sachs Disease.

Autosomal Recessive Example

Autosomal Dominant

• Disease is common in the family (many affected

family members)

• Males and femalesare equally likely to inherit this

disease.

• Disease will never skip a generation– a child

cannot inherit the disease if both parents are
healthy!

• Examples: Achondroplasia (dwarfism),

Huntington’s Disease, Neurofibromatosis

Autosomal Dominant Example

Sex-Linked Recessive

• Disease is rare in the family (only a few

affected family members)

• Disease often skips generations
• Males are more often affected than

females

• Affected fathers DO NOT pass on to

their sons!(Why??)

• Examples: Hemophilia, Duchene Muscular

Dystrophy, Colorblindness

Sex-Linked Recessive Example

How to determine the pattern of

inheritance in a pedigree:

1.

If there are way more males than females affected
(shaded in,) than the pedigree is tracing a
Sex-Linked trait.

2.

If not, look for two parents that are the same shade
that have a child who is different from them. Label
that child homozygous recessive (Ex. rr) and the
parents heterozygous (Ex. Rr)

a.

If the child was shaded, the pedigree is tracing an
Autosomal Recessive trait.

b.

If the parents were shaded, the pedigree is tracing an
Autosomal Dominant trait.

Example #1

Determine the inheritance pattern and label the genotypes.

Autosomal Recessive

Rr

Rr

rr

rr

rr

rr

R?

R?

Rr

Rr

R?

Rr

Rr

Example #2

Determine the inheritance pattern and label the genotypes.

Sex-Linked Recessive

XrY

XrY

XrY

XRY

XRY

XRY

XrXr

XRXr

XRXr

XRXr

XRXr
XRXr

Multiple Choice

How many affected females are present? 

• 1

• 2

• 3

• 4

Multiple Choice

What is the symbol for an Affected Male? 

• Half Circle 

• Half Square 

• Full Shaded Circle 

• Full Shaded Square 

Multiple Choice

How many offsprings did generation 2 have? 

• 5

• 8

• 9

• 10

Multiple Choice

How many children in generation III are homozygous dominant? 

• 1

• 2

• 3

• 4

Multiple Select

Assuming a trait is AUTOSOMAL RECESSIVE, what genotypes would make a person UNAFFECTED?

• AA

• Aa

• aa

• X^AY

• X^aY

Multiple Choice

The genotype X^aY represents a ________

• dominant male

• recessive male

• dominant female

• recessive female