Genetics Flashcards
(33 cards)
mutations
replace, add, or delete a nucleotide base which can result in new traits
- are only relevant to evolution if they are present in the germline
silent mutation
aka a synonymous mutation where the codon is different but the amino acid stays the same
bad mutations
they will cause death or will be selected out as opposed to advantageous ones that will improve their fitness and will be selected for
causes of mutations
are mistakes in replication or by mutagenic stress caused by chemical or physical mutagens like ionizing radiations, UV rays, ROS, or intercalating agents which cause insertions
Eukaryotes can…
use several mechanisms to detect & correct mutations but aren’t 100% effective
6 Classifications of Mutations
- SNPs- 1 base pair is changed
- Indels- insertions & deletions of 1-3 base pairs in DNA
- VNTRs- triplets repeated
- Transposable elements- sequences of DNA move by themselves within a genome
- structural polymorphisms- changes in chromosome structure
- chromosome abnormalities- altered # of chromosomes
SNPs
- 1 base pair is altered
- Synonymous: Amino Acid still stays the same
- Nonsynonymous: substitution, a new AA is added, can even cause truncation of the protein
-Ex: Sickle cell
Indels
- insertion/deletion of 1-3 base pairs in DNA
- Frameshift mutation: happens in a protein coding sequence and can completely alter the whole protein sequence
- 10-fold less frequent than SNPs
- Ex: cystic fibrosis
VNTRs
- Short nucleotide sequences that tandem repeat
- Slippage during replication and recombination can cause repeats to be added or removed from the VNTR which leads to alleles with different numbers of repeats
- The more repeats there are the higher the chance there is to have more repeats which causes slippage
- Microsatellites: 2-4bps and 10-30 repeats
- Minisatellites: 10-100 bps and up to 1000 repeats
- Satellites= several hundred bps which are centromeres, they are diff for all people and mutations here don’t affect the phenotype because its not coding for genes
- Used in DNA profiling for kinship analysis and forensic identification (look at satellites)
- Affected by error during replication = greater mutation rates
-Example: Huntington’s Disease
Transposable Elements (TEs)
- can create, reverse, and alter genome size so it creates genetic diversity
- about 40% of DNA is made of TEs and about ½ of DNA used to move
- HIV is an example of a retrovirus disease
- Hemophilia is example of Alu dysfunction
- 2 classes of TEs
1. Retrotransposons
2. DNA transposons
Sickle Cell Anemia process
example of SNP
-Beta- globulin is changed from GLU to Val on the 6th AA so it goes from Hb to HbS
-Cell sickles (polymerizes) once it reaches deoxygenated blood (venous)
-This means the ion gates on the surface are affected so the electrolyte balance is off where there is high conc. of Ca+ and low conc. of K+
-The RBC dehydrates because of the K+ leakage since water follow K+
-This imbalance of Ca+ creates a hostile environment for plasmodium (malaria)
-The cell becomes sticky
affects of sickle cell
-Venule occlusion leads to: microinfarction (tissue death), ischemic tissue pain (b/c of clotting), ischemic organ malfunction (b/c clotting), auto infarction of spleen because the ability to recycle RBC is shorter since they have lower lifespans now
-Shortened RBC lifespan can lead to: anemia due to loss of RBCs, jaundice b/c bilirubin accumulates in the process of hemolysis, gallstones b/c of bilirubin buildup, leg ulcers due to lack of oxygen supply b/c of anemia
Sickle cell disease
homo recessive, lower life expectancy
sickle cell trait
hetero, incomplete dominance, normal life expectancy but risk of crisis under certain circumstances like high altitude and exercise
malaria and sickle cell
-Mosquito born disease caused by parasitic protozoan’s aka plasmodium falciparum
-Sickle cell carriers are resistant to malaria because the Ca+ increase creates a hostile environment for plasmodium and the shortened lifespan of RBCs also impairs plasmodium survival
-Malaria and sickle cell coevolved together where heterozygotes of sickle cell are resistant to malaria without severe anemia
cystic fibrosis
- indel mutation
- It’s the accumulation of thick mucus secretions in the lungs, intestines, pancreas which greatly increases the risk for infection
-most common mutation: deletion of Phe at position 508 on the CFTR gene (70% of all mutations for cystic fibrosis)
-lifespan has been improved from 5 to 37 years
-treatments: organ transplants (permanent solution) and releasing the mucus
cystic fibrosis chemical process
-mutation in the gene that codes for CFTR Cl- channels
-normal: phosphorylation causes ATP to bind and opens Cl- channel to let Cl- out and water follows it
-mutation causes: Cl- to accumulate inside the cell so it retains lots of water so outside of the cell thick (dehydrated) mucus accumulates
Huntington Disease
- VNTR mutation
- caused by the expansion of a triplet
- almost full penetrance: if you inherit the alleles you will get huntingtins (over 40 repeats)
- low rate of new mutation
-More severe repeats = more severe disease
-function in neuron differentiation/proliferation and thus brain development/function
-CAG repeats: glutamine
-The more repeats you have the earlier onset you have, avg onset 30-50
-It develops after people typically have kids, so the trait is passed on and not selected out
penetrance
what portion of people with the genotype will also express the phenotype
anticipation
new generations have more severe signs and symptoms because the more repeats there are the more repeats are likely to continue to occur
Huntington’s signs/symptoms
chorea (involuntary movement), paranoia/depression/mood disorders, dementia, slurred speech, unsteady gait, anticipation (shows earlier in later generations)
Retrotransposons
Retrotransposons: transcribed from DNA to RNA then RNA is reverse transcribed (this step is catalyzed by a reverse transcriptase) to DNA and inserted back into genome at a new position.
- The reverse transcription is catalyzed by reverse transcriptase which is why many transposons originated from retroviruses
-most retrotransposons are of ancient origin and can no longer move while younger ones can still move and are used to mark ancestry
-retrotransposons can disrupt protein coding and regulatory regions
retroviruses
are single stranded RNA viruses that replicate their genetic materiel with a reverse transcriptase that they inject into the host cell where it is reverse transcribed into DNA and inserted into the hosts DNA so now it can produce viral proteins like HIV
- Insert RNA – reverse transcriptase – into DNA – insert DNA into hosts DNA – creates new virus with reverse transcriptase RNA
DNA transposons
DNA transposons: a portion of DNA is removed and the DNA intermediate is inserted into the target DNA to create a new strand of DNA
