Intro to Medical Genetics Flashcards
A gene is a segment of DNA that encodes for a specific
a) protein
b) tRNA
c) rRNA
d) microRNA
e) all of the above
e
Define an allele
Alternative forms of a gene (DNA at a specific locus) that differ in sequence
Define a locus
A physical region of a chromosome; often used to refer to a segment of DNA that contains a specific gene
Homologous chromosomes are chromosomes that ______ during meiosis, ____ from each parent
pair, one
Are homologous chromosomes identical?
No, normally only a few base pair differences in each gene
Are sister chromatids identical?
Yes, two identical duplicated chromosomes joined by a single centromere
During which cell replication cycle would you find sister chromatids?
Metaphase
What are autosomes?
ANy chromosome that is not a sex chromosome
An organism with 4 copies of each chromosome would be ________
tetraploid
A human has 45 chromosomes in a cell. He is a _____________ (type of ploidy)
Aneuplod
A human has 69 chromosomes in a cell. He is a ____________ (type of ploidy)
Euploid - abnormal but still same number of each homologous chromosome
Germline cells are responsible for _____________________
production of gametes
What are gametes
haploid germ cells (sperm and ova)
What are zygotes
Two gametes fuse (during fertilization), diploid
Homologous chromosomes have _______ genes in ______ positions, but _______ alleles
(same/different)
same, same, different
Why is neonatal screening done?
To ID rare disorders that can cause brain damage or death if not treated early ie PKU
Describe prophase of mitosis
chromatin condenses (chromosomes with two chromatids) –> spindle forms –> nucleolus breaks down
Describe prometaphase of mitosis
spindle invades nuclear region, chromosomes move to equatorial plane
Describe metaphase of mitosis
Chromosomes at equatorial plane and centromeres divide
Describe anaphase of mitosis
poles move apart and chromosomes move towards destinations
Describe telophase of mitosis
Spindle breaks down –> chromatid uncoils –> nucleoli formed –> contractile ring causes cytokinesis
What is the product of cytokinesis in mitosis?
Two daughter cells, each genetically identical to parent cell
Describe prophase I of meiosis
Homologous chromosomes pair up and exchange fragments (cross over)
Describe metaphase I of meiosis
Homologous pairs line up at metaphase plate
Describe Anaphase I of meiosis
Homologues separate to opposite ends of cell, sister chromatids stay together
Describe Telophase I of meiosis
Newly formed cells are haploid, each chromosome has two (non-identical) sister chromatids
Meiosis II is very similar to mitosis. What are the two differences?
1) Haploid (2n) cells at beginning rather than diploid (4n)
2) Creates 4 haploid cells, with chromosomes having one chromatid each
What is the key difference between meiosis and mitosis?
During prophase homologous chromosomes synapse - pair up tightly and there is genetic exchange (evidenced by chiasmata)
Describe synapsis
Pairs of sister chromatids align according to homologous sequences and are bound together –> crossing over occurs
What is the product of crossing over? (type of chromosome)
recombinant!
What are the 4 components of gene structure?
1) promoters
2) coding sequences (exons)
3) introns
4) structural regions (non-transcribed, 5’ and 3’ untranslated sequences)
What causes genetic disorders
a) changes in DNA
b) changes in RNA
c) changes in protein level/activity
c
What type of mutation in Hgb causes sickle cell anemia?
single base pair change
Function of promoter sequence
controls levels of mRNA expression –> controls protein expression
Function of introns
“intervening sequences”
interrupt coding sequences
spliced out
Function of exons
Coding sequences
Specific sequence of AA in proteins
Function of structural regions
Untranscribed regions
5’ and 3’ untranslated regions in mRNA
The TATA box is a promoter sequence that specifies to other molecules ____________________
where transcription begins
The CCAAT box is a distinct pattern of nucleotides with consensus sequence that occur upstream by ___________ bases to _______________
60-100, initial transcription site
The core basal promoter determines ______ site for transcription and ____________
start, whether transcription occurs
Describe the function of an enhancer
Short region of DNA that can be bound by activator proteins to increase the likelihood that transcription of a particular gene will occur
Tissue specific elements say _____ and _____ a gene is transcribed
when and where
Describe the function of regulatory elements
Determine when, where and how much transcription occurs
Intron mutations are usually harmful, true or false
False, only mess things up when located in splice zone
What percentage of a gene is not transcribed?
70%
What percentage of a transcript is structural?
70%
All combos beginning with CG will produce ______
ARGININE
A point mutation that does not change the amino acid is called a
silent mutation
A point mutation that does change the amino acid, but only to another with similar biochemical properties is called a
missense mutation
A point mutation that introduces a premature stop codon
nonsense mutation –> truncated protein
Does the addition of 3 nucleotides qualify as a frame shift mutation?
no. Can still be harmful examp: delta f508
A promoter mutation would affect _______
levels of protein expression
Tertiary post translational processing involves
Interdomain interactions
Quartanery post translational processing involves
multiple polypeptide complexes
Loss of function mutations lead to (2)
inactive protein products OR loss of expression
PKU and Cystic Fibrosis are examples of haplosufficiency diseases. What does this mean?
One normal allele is enough to not have disease
DOMINANT
Familial hypercholesteremia is a haploinsufficiency disease. What does this mean?
One bad allele and you’re f**ked
RECESSIVE
Gain of function mutations lead to (2)
new protein product OR overexpression/misexpression (in wrong tissue of a normal protein
Huntington’s Disease and the trisomies are caused by what type of mutation?
gain of function
Osteogenesis Imperfect II is an example of a dominant negative disease. What does this entail?
Mutant protein inhibit activity of normal protein
What does it mean to be reproductively lethal?
Organism can have mutation and live with it but cannot pass it on to next generation
Reproductively lethal mutations are always ______
spontaneous and new
Recessive disorders are always spontaneous new mutations, true or false
FALSE - rarely, X linked disorders present a special case
What are the three ways a silent mutation can occur
1) in non essential sequences (introns, untranslated structural regions)
2) occur in redundant base (no AA change)
3) result in a conservative substitution that does not change protein structure or function
