Take out CHNOPS activity No Warm-Up Today Take out CHNOPS activity

Section 12.4 (Causes, Examples) 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?

Preventing Genetic Disorders in Embryos…and beyond? “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?