Download File - Down the Rabbit Hole

Human Genetic
Mutations
•
Mutations are a result in a change in DNA
sequence
– A protein with a different AA sequence could be
produced.
– Germ Cell - If mutations occur in sex cells they may
be passed on to the next generation.
– Somatic- A mutation occurring only in body cells
may be a problem for the individual but will not be
passed on to the offspring.
•
Mutations may be classified as chromosomal
alterations or gene mutations
– Chromosomal alterations are generally more severe
because many genes are usually involved.
2 Main Types of Mutations
1.) Chromosomal Mutations
2.) Gene Mutations
Chromosomal Mutations
• Any change in the structure
or number of chromosomes
• Large scale: Affect many
genes
Gene Mutations
• Small scale: one gene
is affected
• Any change to the DNA
sequence of a gene:
Nucleotides/Bases may be
added, missing, or
changed
Significance of Mutations
Most are neutral
• Eye color
• Birth marks
• Some are harmful
• Cystic Fibrosis
• Down Syndrome
• Some are beneficial
• Sickle Cell Anemia to Malaria
• Immunity to HIV
•
What Causes Mutations?

There are two ways in which DNA can become
mutated:
– Mutations can be inherited.
 Parent to child
– Mutations can be acquired.
 Environmental damage
 Mistakes when DNA is copied
5 Types
1. Deletion
2. Duplication
3. Inversion
1. Pericentric
2. Paracentric
4. Translocation
5. NonDisjunction
Chromosomal Deletion
One or more genes are removed
Causes:
Wolf-Hirschhorn syndrome (severe mental retardation)
cri du chat syndrome (mewing sounds, mental retardation)
Chromosomal Duplication
A segment of genes is copied twice and added to
the chromosome
Causes:
Charcot–Marie–Tooth disease
(high arched foot, claw feet, confined to a wheelchair)
Chromosomal Inversion
a segment of genes flip end-to-end on the chromosome
Causes:
Four-Ring Syndrome
(cleft pallate, club feet, testes don’t descend)
Chromosomal Translocation
Material is swapped with another chromosome
Causes:
Burkitt’s Lymphoma
(cancer of the lymph nodes, in children)
Nondisjunction
• Chromosomes FAIL TO
SEPARATE during meiosis
• Meiosis I Nondisjunction
• Meiosis II Nondisjunction
Nondisjunction
• Produces gametes (and therefore a
baby) with one missing
chromosome or one extra
chromosome
KEY POINT #1
Too much or too little DNA is bad!
Gene Mutations: 2 Types
Point Mutation
Frameshift Mutation
•
Point mutation
•
Only one nucleotide changes, but it
makes a different protein
Point Mutation
• One base (A, T, C, or G) is substituted for another
• 3 Possible Consequences:
– nonsense mutations: code for a stop, which can
translate the protein
– missense mutations: code for a different amino
acid
– silent mutations: code for the same amino acid
Gene Mutations

Point Mutations – changes in one or a
few nucleotides
– Substitution
 THE FAT CAT ATE THE RAT
 THE FAT HAT ATE THE RAT
– Insertion
 THE FAT CAT ATE THE RAT
 THE FAT CAT XLW ATE THE RAT
– Deletion
 THE FAT CAT ATE THE RAT
 THE FAT ATE THE RAT
Frameshift Mutation
• One or more bases (A, T, C, or G) are
added or deleted
• Caused by:
– Insertion: adding a base
– Deletion: removing a base
•
Frameshift
•
Causes every codon in the DNA sequence to be changed after the
mutation:
• Insertion- one or more bases are added
• Deletion- one or more bases are removed
A
Causes of Mutations
• spontaneous
• occur during DNA replication
• Caused by MUTAGENS
• physical, ex: radiation from UV rays, X-rays or
extreme heat
• or chemical (molecules that misplace base pairs or
disrupt the helical shape of DNA).
Gene Mutations
• KEY IDEA: A mutated gene will make a
mutated protein
• Mutant proteins are trouble!
–They do not go where they are
supposed to go
–They do not do what
they are supposed to do
KEY POINT #2
Mutation of a gene = Mutant protein
Dysfunctional proteins cause the
symptoms of the disorder
Length of Telomeres
telomeres
Telomeres are
structures at the ends
of chromosomes that
shorten with each cell
division. After 50
divisions, the
shortened length of
telomeres causes
mitosis to stop.