2B- Genetic Variation Flashcards
What is a base substitution?
It’s a single gene mutation in which one base pair is replaced by another. In molecular genetics it’s called point mutation
What is a silent substitution?
Does not change the amino acid sequence and have no consequences
What is a missense mutation?
Produce a change in single amino acid
What is a nonsense mutation?
Produce one of the three stop codon (UAA, UAG, UGA) causing premature termination of the polypeptide chain
What happens in a deletion and insertion mutations?
It can result in extra or missing amino acids in a protein, often detrimental
What is a frameshift mutation?
When the number of missing or extra base pairs is not a multiple of three. This changes the entire reading frame from that point on.
What is a duplication mutation?
duplication of the whole gene
What happens at splice-site mutations?
Happens at intron-exon boundaries, alter the spicing signal that is necessary for proper excision of an intron
What is a promoter mutation?
It decreases the affinity of RNA polymerase for a promoter site, often resulting in reduced production of mRNA and reduced production of a protein
What is an enhancer mutation?
Mutation in the enhancer region of the DNA which results in reduced protein production.
What are expanded repeat mutations?
affects tandem repeated DNA sequences that occur within or near certain disease-related gene
What are gain of function mutations?
They result in overexpression of the product or inappropriate expression. It produces dominate disorders
What genotype results in loss of function mutations?
recessive diseases
What genotype in loss of function mutations is sufficient for normal function?
hterozygous. 50% of the protein product is lost but the 50% that remains is sufficient for normal function
What are the normal subunit genes of adult Hb?
Normal individual has two normal βgenes and four normal α genes and is associated with a heme group
What populations are mostly affected by sickle cell disease?
Affects mostly African-American, Middle Eastern and Mediterranean population
***What is the cause of sickle cell disease?****
single missense mutation that affects a substitution of a valine for glutamic acid at position 6 of the β-globin polypeptide chain
What is generalized thalassemia?
α & β globin chain is structurally normal but reduced in quantity
What is α-Thalassemia?
α-chain is reduced and there are excess β-chains
What are the main causes of α-Thalassemia?
deletions of the α-globin genes
What is HbH disease?
The loss or abnormality of three of the α-genes
What are the clinical manifestations of HbH disease?
IT produces moderately severe anemia and splenomegaly
What is the cause of hydrops fetalis?
Loss of all four α-genes
What are the clinical manifestations of hydrops fetalis?
Condition in which there is a massive buildup of fluid.
What is β- Thalassemia?
β-chain is reduced & excess α-chains
What are the issues with excess α-chains?
Excess α-chain causes precipitation and damages the cell membranes of red blood cell precursors. This leads to premature erythrocyte destruction and anemia
What is β-Thalassemia minor?
Mutation in one copy of chromosome 11. It involves little or no anemia and does not ordinarily require clinical management.
What is it called when β-globin is completely absent?
β^0-Thalassemia
What is it called when β-globins are reduced to about 10-30% of the normal amount
β+ Thalassemia
What is HPFH?
(hereditary persistence of fetal hemoglobin): occurs when fetal hemoglobin, encoded by the α-globin genes and by two β-globin like genes called Aγ & Gγ continues to be produced after birth
How can ionizing radiation cause mutations?
They form electrically charged ions that change DNA bases or can break dsDNA
What type of cells can ionizing radiation affect?
This kind of radiation can reach all cells of the body including the germ line cells.
What type of mutations can UV radiation cause?
UV radiation causes the formation of covalent bonds between adjacent pyrimidine base (pyrimidine dimers)
What are base analog mutations?
5-bromouracil has chemical similarity to DNA bases. It can substitute for a true DNA base during replication. It’s not exactly the same as the base it replaces, so it can cause pairing errors during subsequent replication
What types of mutations can acridine dyes cause?
physically insert themselves between existing bases, distorting the DNA helix and causing frameshift mutation
What types of mutations can nitrous acid cause?
removes an amino group from cytosine, converting it to uracil. It mimics the pairing actions of thymine in DNA and pairs with adenine instead of guanine. Ending in base pair substitution
How does size of a gene relate to mutation rate?
Larger genes present larger “targets” for mutation and usually experience mutation more frequently than smaller genes
What are mutation hot spots?
Mutation hot spots are certain nucleotide sequences that are especially susceptible to mutation
What 2 base sequence allows of 80% of them to be methylated?
CG
How does age relate to mutation rate?
Some chromosome abnormalities increase dramatically with maternal age
What is Xeroderma pigmentosum?
when there is a defect in the enzymes that are supposed to repair those pyrimidine dimers that are formed via UV radiation
What type of repair is defective in xeroderma pigmentosum?
nucleotide excision repair
What are some clinical manifestations of xeroderma pigmentosum?
skin tumors, photosensitivity, cataracts, and neurological abnormalities.
Where is the ABO system is encoded?
chromosome 9
What is Rh factor?
Rh is defined on the basis of antigens that are present on erythrocyte surfaces. This can cause maternal-fetal incompatibility.
What is the multiplication rule?
rule states that if two trials are independent, that the probability of obtaining a given outcome in both trials is the product of the probabilities of each outcome.
What is the addition rule?
states that if we want to know the probability of either one outcome or another, we can simply add the respective probabilities together
What is the Hardy-Weinburg equation?
P2+2PQ+Q2=1
P= Normal allele (A)
Q=Mutated allele (a)
Because there are two allele P + Q=1
Frequency of the homozygote A=P2
Frequency of heterozygote Aa= 2PQ
Frequency of the mutated homozygote a =Q2
Give the frequence of AA and Aa in an autosomal recessive inheritance with a incidence of 1/10,000
P2+2PQ+Q2=1
For a disorder with an incidence of 1/10000 persons, q2=1/10000 & q=1/100
p= 1- (1/100) or 99/100 and the frequency of AA is p2= 98/100
The frequency of the heterozygote is 2pq~ 1/50
What is the frequency of the mutant allele in an autosomal dominant inheritant disorder?
The incidence of the disorder in the population=2pq
The frequency of the mutant allele= half the incidence
For simplicity, the homozygous affected individuals are ignored because such diseases are typically lethal.
For a population to be in Hardy-Weinberg equilibrium what conditions must be met?
What exactly are gene frequencies?
it is defined as the proportion of a population’s chromosomes that have a specific allele.
What is natural selection?
It is often described as “editor” of genetic variation. It increases the population frequency of favorable mutation and it decreases the frequency of genes that are unfavorable in a given environment
What is genetic drift?
It’s another force that can cause disease genes to vary in frequency among populations.
The larger the population, the less random fluctuation from expected frequency of allele distribution.
What is gene flow?
This occurs when population exchange migrants who mate with one another. Through time, gene flow between population tends to make them genetically more similar to one another
What is the “founder effect?”
Certain diseases are “founded” in a certain area then it is spread via genetic drift to other population throughout the world
