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Take out CHNOPS activity
DNA
Mutations!
Section 12.4
(Causes, Examples)
What is a Mutation?
• Mutation: DNA is changed
– Occurs because of:
• Incorrect copying in DNA synthesis
• Incorrectly made mRNA strand in
transcription
• Outside radiation, etc. disrupts DNA
•
Can be gene or chromosomal mutations
Gene Mutations
• Change to one or a few nucleotides on a
gene (segment) of DNA
• Point mutation
- Substitution: put an ‘A’ instead of a ‘G’,
etc.
- Substitutions disrupt one amino acid
- Substitutions rarely cause a genetic
disorder as proteins can still function with
only one incorrect amino acid
Sickle Cell Anemia
• In Sickle Cell Anemia, a substitution has
occurred on chromosome 11 so that the protein
hemoglobin is made incorrectly
• Distorts shape of red blood cells so they can’t
carry oxygen well
• Most common in tropical areas as
this mutation actually prevents
malaria (Plasmodium can’t infect
sickle shaped cells)
Gene Mutations
• Insertion or Deletion are ‘Frameshift
Mutations’
– By inserting/deleting a nucleotide, the 3 letter
mRNA reading system is shifted by one letter
– Therefore, every amino acid is incorrect and
the entire protein is useless
– More common cause of genetic disorders
– If this mutation is in a developing fetus, every
cell makes the incorrect protein!
Gene Mutations:
Frameshift
Cystic Fibrosis
• Caused by insertion of two letters in the
CFTR gene on chromosome 7
– Causes cells to secrete thick, sticky mucus
that impedes lung function
– Usually fatal
– 1 in 1600 Caucasians
have CF; 1 in 29 carry
the recessive gene
Tay Sachs Disease
– The HEXA gene on
chromosome 15, which makes
an enzyme that breaks down
extra lipids, is ineffective due to
a deletion
– Extra lipids build up in brain
cells, impairing motor function
and causing death
• 1 in 5000 have the disorder;
• 1 in 250 are carriers
• 1 in 27 people of Jewish descent
are carriers
Chromosomal Mutations
• Change in number or
structure of whole
chromosome
Example: People with
Down Syndrome have
an extra chromosome
21 in every cell
Effects of Mutations
• Most mutations are non-harmful
• Some mutations increase genetic variation
in a population, helping them survive
better!
– Pandas have a ‘thumb’
that is an enlarged wrist
bone from a mutation
- Those with the mutation
survived better because
they could hold bamboo!
How are mutations inherited?
• One or both parents will carry a ‘mutant
gene’ that causes a disorder
– If this gene is ‘recessive’ they don’t have the
disorder but are carriers
– If this gene is ‘dominant’ they have the
disorder
– In chromosomal mutations, one parent gives
an extra chromosome, mutant chromosome,
or doesn’t give one at all
• If both
parents
are
carriers,
the baby
has the
disorder
and they
don’t!
How are mutations inherited?
• The gene is carried in the sperm or the
egg and passed on to the offspring when
the egg is fertilized
• Parents don’t know if the baby has the
disorder until it has health problems from
the incorrectly made proteins
• Is there some way to prevent embryos
from having genetic disorders?
“Designer
Babies”
Preventing Genetic Disorders in
Embryos…and beyond?
Creating and Screening Embryos
• Through In-Vitro Fertilization, human
embryos can be created and analyzed in a
lab
– In Vitro = egg and sperm are harvested from
parents, fertilized, and implanted back in the
mother
Creating and Screening Embryos
• A single cell can be removed
from an 8 day old embryo before
it is implanted
• The cell is analyzed for gender
and 200+ identified genetic
disorders
– The DNA of the embryo’s cell is
run through a computer program
that compares the sequence to
‘normal’ genes to identify a
disorder
What‘s legal? What’s ethical?
• It is currently legal in the U.S. to screen for
genetic disorders and gender and to
choose embryos based on the outcome
• Not restricted to only couples carrying
genes for genetic disorders
– Should it be?
– Are we headed down the slippery slope of
designing our children?
Reading Assignment
• With your table partner, determine who is
the stronger/faster reader
• The stronger reader takes the “Brave New
Babies” article and the other person takes
the “Outcry” article
• Read and answer these questions on
notebook paper:
Reading Assignment
• What are scientists capable of doing in
regard to human embryos?
• What are the benefits?
• What are the drawbacks?
• Should PGD (pre-implantation genetic
diagnosis) be allowed for everyone? Why
or why not?