Transcript Mutations and other genetic problems

Mutations and other genetic
issues
Genetics Unit
Mutations
Changes in the genetic material.
 Any deviation from the normal
chromosomal compliment
 Two types:

Spontaneous mutations-occur randomly; no
cause can be determined
 Induced mutations are caused by some
traceable artificial factor: exposure to
chemicals, alcohol, drugs, radiation

Mutations
Mutations that produce changes in a
single gene are gene mutations.
 Mutations that produce changes in a
whole chromosome are chromosomal
mutations.

Gene Mutations

Point mutation-change in one or just a
few nucleotides. So named because it
occurs at a single point.
Substitutions
 Deletions
 Insertions

Gene Mutations

Frameshift mutation—shift the reading
frame of the genetic code

Can alter a protein so much that it can’t
perform its job.
Chromosomal Mutations
Involve a change in the number or
structure of the chromosome
 Some change the location of some
genes on the chromosome
 Some may change the number of copies
of some genes.

Chromosomal Mutations

Four main types of mutations:
Deletion
 Duplication
 Inversion
 translocation

Deletion
The permanent loss of a segment of
chromosome
 Can be found anywhere on the
chromosome
 Can be caused by heat, radiation,
viruses, chemicals, errors

Deletion
Duplication
Doubles a segment of chromosome
 Can be fatal
 Can be caused by uneven crossing over
during meiosis or replication error before
meiosis

Duplication
Causes of abnormalities

Nondisjunction
The failure of the chromosome pairs to
separate during Meiosis I or Meiosis II
 Result will be a zygote with too many or too
few chromosomes
 Two types: Primary and secondary
nondisjunction

Primary Nondisjunction
Secondary Nondisjunction
Types of Genetics Tests
When trying to determine a genetic
problem, we can use non-invasive tests
such as
 Pedigrees
 Karyotypes

Pedigrees
A pedigree follows a specific trait through
several generations
 Resembling a type of map, the pedigree
uses symbols to represent certain
elements

Pedigree key
Pedigree
Karyotypes
A photographic inventory of an
individual’s chromosomes
 Can show the individual’s gender and
any abnormalities in chromosome
number or structure

Karyotypes
Karyotypes
Amniocentesis

An invasive test that obtains amniotic
fluid surrounding the fetus using a
needle
Amniocentesis Pros and Cons
Able to determine fetus’ gender and/or
any abnormalities
 Can’t be done before 16th week of
pregnancy
 Can cause infection to mother and/or
fetus
 Can cause premature delivery and birth

Chorionic Villus Sampling (CVS)
CVS Pros and Cons
Can determine fetus gender and any
genetic abnormalities
 Can be done after 10 weeks
 Can cause leakage of amniotic fluid
 Can cause premature labor and delivery

Recessive Disorders
Must be inherited from BOTH parents
 Autosomal recessive disorders (non-sex
cells)

Tay-Sachs
 PKU
 Cystic fibrosis

Recessive Disorders

Tay-Sachs—lipid accumulation in the brain;
mental deficiency; blindness, death in early
childhood
 PKU-phenylketonuria—accumulation of
phenylalanine in tissues; lack of normal skin
pigment; mental retardation
 Cystic fibrosis—excess mucus in lungs,
digestive tract, liver; increased susceptibility to
infections; often die young
Dominant Disorders

Can get the disorder by inheriting only
one dominant allele
Huntington’s disease
 Achondroplasia

Dominant Disorders

Huntington’s Disease
Mental deterioration and uncontrollable
movements
 Doesn’t appear until middle age


Achondroplasia

One form of dwarfism
Sex Linked Disorders

Is there a pattern of inheritance for genes
located on the X or Y chromosome? YES
especially on the X
 Many times it is male children that inherit
these disorders from their mothers because . .
. They inherit their X from their mom’s
Many sex linked genes are on the X



Colorblindness
Hemophilia
Duchenne Muscular Dystrophy
Sex Linked Disorders

Colorblindness

Most often found in males


1 in 10 males
Females have to inherit from both parents
1 in 100 females
 Most common is red-green colorblindness

Sex Linked Disorders

Hemophilia
Two genes on the X chromosome control
blood clotting
 Many times it is male children that inherit
this from their mom’s X chromosome
 1 in 10,000 males
 A bleeding disorder; can cause death in
severe cases

Sex Linked Disorders

Duchenne Muscular Dystrophy
1 in 3000 males
 Progressive weakening and loss of skeletal
muscle
 Caused by defective version of gene that
codes for a muscle protein

Genetic Disorders

Trisomy
Downs Syndrome (extra chromosome 21)
 Edwards Syndrome (extra chromosome 18)
 Patau Syndrome(extra chromosome 13)

Downs Syndrome (Trisomy 21)
Edwards Syndrome (Trisomy 18)
Patau Syndrome (Trisomy 13)
Turner’s Syndrome
Turner’s Karyotype
Klinefelter’s Syndrome