Lecture 8: Molecular Genetics Flashcards
What do genetics determine?
Disease susceptibility
How we react to drugs
Our appearance
What are the 4 bases of DNA? RNA?
DNA:
Adenine
Guanine
Cytosine
Thymine
RNA:
Adenine
Guanine
Cytosine
Uracil
What is mitochondrial DNA inherited from?
Mom AKA MATERNAL
How many amino acids are there?
20
How many codons are there?
64
What are synonyms in codons?
Codons that only differ at the third base (they usually code the same AA or similar AA)
What is monogenic? Polygenic?
Single alleles
Multiple alleles
What defines a polymorphism?
A specific genetic change that does not have an associated phenotype change.
What kind of DNA changes can be inherited?
DNA in gametes only.
What is penetrance?
The ability of a gene to express a mutation.
What are the common types of mutations? Most common?
Most common is a SNP, or single nucleotide polymorphism.
Nonsense mutation: substitution causing an AA to be changed to a stop codon.
Missense mutation: substitution causing an AA to be changed to a different AA.
Splice site mutation: substitution near the intron-exon boundary, causing a skip in reading.
Silent mutation: substitution resulting in no change in AA
Regulatory polymorphism: substitution causing a change in binding affinity, affecting transcription.
What are the three types of RNA?
mRNA (messenger RNA)
rRNA (ribsomal RNA)
tRNA (transfer RNA)
When is mRNA formed?
During transcrption.
What is the purpose of rRNA?
Makes up the ribosomes that perform translation.
What is the purpose of tRNA?
Delivers the amino acid, recognizing and binding it.
What is transcription?
Copying DNA to form the complementary strand of RNA.
Where does transcription occur?
In the nucleus.
What are exons and introns? Why are they significant?
Introns and Exons are segments of RNA/DNA. We skip introns when going from RNA to mRNA, so mRNA is made only of EXONS.
Where does translation occur?
Cytoplasm, on the ribosome
How many chromosomes does a somatic cell have?
23 pairs
How many chromosomes are sex chromosomes?
2 (X and Y)
What is the difference between mitosis and meiosis?
Mitosis is for somatic cells, same genetic makeup.
Meiosis is for gametes, half the genetic makeup.
What is recombination?
Chromosomes separating and coming back together.
What is nondisjunction?
Failure of chromosomes to separate
What is aneuploidy?
Unequal amount of chromosomes being passed on
When does nondisjunction usually occur?
Oogenesis
Who is most at risk for aneuploidy?
30+ (increasing as you get older)
under 16
females
If I have disjunction in Meiosis I, how many erroneous gametes will I have?
4 (AKA all of them.)
2 will have one less chromosome
2 will have one more chromosome
If I have disjunction in Meisosis II, how many erroneous gametes will I have?
2
1 will have one less chromosome
1 will have one more chromosome
What is monosomy and the one exception?
Having one less chromosome in a pair. This usually is incompatible with life.
Exception: Turner syndrome, where you have 45 chromosomes because you only have an X chromosome.
What is Turner syndrome? Characteristics?
Lack of a second sex chromosome, so they are genetically X and therefore female.
Involves short stature, wide-set nipples, webbed neck, lack of secondary sex characteristics.
Normal intelligence.
Diagnosed most commonly due to short stature or failure to enter puberty.
What is polysomy? Examples?
Presence of more than 2 chromosomes in a set.
Trisomy 21: Down syndrome (most common)
Trisomy 13 & Trisomy 18 (Edward syndrome): Not compatible with life usually.
Trisomy of sex chromosomes:
47 XXX = triple X syndrome
47 XXY = Kleinfelter syndrome
What is Trisomy 21 more commonly known as? Characteristics?
Down syndrome, commonly caused by Nondisjunction in meiosis (95%)
Most common chromosomal disorder.
Flattened nasal bridge, epicanthal folds, protruding tongue, simian crease
Often found during prenatal screening.
What is XXY syndrome more commonly known as? Characteristics?
Kleinfelter syndrome: caused by disjunction during maternal meiosis most commonly.
Affects 1 in 1000 males.
Enlarged breasts, sparse body hair, small testes, high voice
Infertility & osteoporosis later
Treated via androgens
What is mosaicism?
Presence of two or more genetically different sets of cells, caused by early mitosis errors.
AKA certain areas of the body can be genetically different.
What is genetic linkage?
Genes in close proximity sort together.
What is the main structural abnormality that occurs?
Translocation: large segment of DNA breaks off a chromosome and attaches to a different chromosomes, most often during meiosis.
Causes Familial Down syndrome, which is translocation of chromosome 14 to 21.
What are the types of structural abnormalities in chromsomes?
Deletion
Duplication
Inversion
Insertion
Translocation
Ring chromosome
Isochromosome
Derivative chromosome
See slide 51 for visual images
What initiates RNA transcription?
RNA polymerase
