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52 Cards in this Set

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How many chromosomes and base pairs in the human genome?
-23 ch'
-700 million base pairs
How much is functional and how much is extragenic DNA?
Extra: 70%
Genes: 30%
Pneumonic for remembering the pieces of a chromosome:
SPLQ
-SHORT = p
-LONG = q
What is between the short and long arm of a chromosome?
The centromere
What do ALL cancers arise from?
Genetic alterations
How much cancer is hereditary?
5-10%
The study and understanding of cancer is transitioning from traditional epidemiology to:
Molecular epidemiology
What is a codon made up of?
3 base pairs
How many codons are there?
64
What do codons encode?
Amino acids
What is a point mutation?
A change in a single base pair
In the original primary sequence of base pairs, what are exons and introns?
Exons: the nonextra stuff
Introns: the nonimportant stuff
OPPOSITE
What is a polymorphism?
A DNA sequence change that does NOT alter protein function.
What is a sequence variant?
A base pair change that does not change the amino acid sequence.
How can there be silent sequence variants?
Because of the redundancy of the genetic code.
What is a Missense mutation?
A change in codon that leads to another amino acid being translated.
Are missense mutations always harmful?
No, they can be neutral polymorphisms.
What is a Nonsense Mutation?
A change that introduces a stop codon where it shouldnt be, resulting in a shorter protein.
What is a Frameshift mutation?
A change that inserts or deletes base pairs and produces a stop codon downstream, with a shorter resulting protein.
What change results from a Splice-Site mutation?
An altered RNA sequence
What are the 3 types of genes associated with cancer predisposition?
1. Tumor suppressor genes
2. Oncogenes
3. DNA damage-response genes
What are tumor suppressor genes?
The cell's brakes for tumor growth
What change in tumor suppressors allows for cancer to arise?
Both brakes fail
What do oncogenes do?
Accelerate cell division
When does cancer arise via oncogene mutations?
When the gas is stuck on
What are DNA damage-response genes?
The repair mechanics for DNA
When does damage to DNA dmg-response genes allow for cancer to arise?
When BOTH genes fail, so mutations accumulate at a faster rate in OTHER CRITICAL GENES.
So what is the hypothesis for how tumor suppressor gene mutations cause cancer?
The 2 hit hypothesis - BOTH BRAKES HAVE TO FAIL.
Where is the first hit?
In the germline dna
HWhat is the hypothesis for how oncogenes cause cancer?
Just one gas pedal - only one mutation is needed
What are the 2 main categories of gene mutations?
1. Germline mutations
2. Somatic mutations
What is a Germline mutation?
One that is present in egg or sperm and is inherited by all of the cells in the affected offspring.
What is a Somatic mutation?
One that occurs in nongermline tissue and is NONinheritable.
What does heterozygosity refer to?
Having one normal allele and one mutant allele.
What are 6 mechanisms that lead to loss of heterozygosity?
1. Chromosome loss
2. Deletion
3. Loss/reduplication
4. Unbalanced translocation
5. Mitotic recombination
6. Point mutation
At what point in the cell cycle do oncogene mutations appear?
Going from G1 to G0 - they accelerate it.
At what point in the cell cycle do tumor suppressor gene mutations appear?
Going from G0 to S phase - they fail to stop it.
At what point in the cell cycle do DNA repair gene mutations appear?
Going from S phase to G2 and mitosis - fail to see that synthesized DNA is damaged.
What do disease-associated mutations result in?
Altered protein function
What does the RET gene illustrate?
That different MUTATIONS in the SAME GENE can cause DIFFERENT SYNDROMES.
What does the BCRA gene illustrate?
That mutations in DIFFERENT GENES can cause the SAME SYNDROME.
What is Carrier frequency?
The prevalence of an altered disease gene in a given population
If 2 of 10 people are carriers of a diseased gene, what is the carrier frequency?
20%
What does Age-specific penetrance show?
The % of people with an altered gene, who actually get the disease as they get older.
What disease shows a substantial increase in age-spcf penetrance as individuals grow older?
HNPCC - hered nonpolyposis colorectal cancer.
What are 4 factors that affect the penetrance of disease with age in carriers of gene mutations?
-Modifier genes
-Responses to DNA damage
-Carcinogen exposure
-Hormonal/repro factors
What factor is associated with increased penetrance of breast cancer?
Estrogen
What is important to remember about those people that do carry an altered gene?
Not everyone with altered genes will develop cancer.
Who is at high risk for hereditary cancer?
Only a small porportion; only about 10% of cancer is hereditary.
What is the key to identifying a hereditary cancer?
The FAMILY HISTORY
How do you do an accurate risk assessment?
By looking as extensively into their pedigree as possible.
What are 6 things that make you suspect hereditary cancer?
-Cancer in 2/more close relatives
-Early age of diagnosis
-Multiple primary tumors
-Bilateral or multiple rare cancers
-Constellation of tumors consistent with spcf cancer syndromes (breast/ovary)
-Evidence of auto-dom transmission