Mechanisms of Creating Genetic Diversity Flashcards
What does deleterious mean?
Deleterious refers to genetic changes that make the organism less suited to thrive in its environment.
Describe chromosomal recombination and its importance
“Crossing over” - between homologous chromosome pairs in meiosis. Allows a germ cell to pass on a mixture of genetic information to subsequent generations. Exchanging info between parental chromosomes maintains genetic diversity without risks of random mutation. 2/3 crossovers per chromosome and can happen anywhere. This combined with random segregation means that no two gametes are genetically identical.
Describe the process of chromosomal recombination
After pre-meiotic replication, the crossover occurs at points called chiasmata. The crossover requires sequence homology between parental chromosomes. Cohesin complexes are required for chiasmata formation.
What is aberrant recombination and how does it affect the genome?
Both copies of the chromosome go into the same cell - zygote has an extra copy of a chromosome, if chromosome 21 it’s Down’s. If a gene is flanked by repeated sequences, chromosome misalingment can occur and during the crossover one chromatid will get two copies of the gene and the other chromatid will have none. If a two copy gamete fertilises with a 1 copy gamete, the zygote has 3 copies which leads to disease. Happens in Charcot-Marie-Tooth disease with PMP22 gene.
How does this type of recombination drive evolution?
If an ancestral cell has a single gene copy on one of its chromosomes, and aberrant recombination occurs, the offspring will have 2 copies on one chromosome. Over time, the 2 copies will diverge, accumulating sequence changes which turns them into distinct genes. They may be translocated due to chromosome rearrangements and diverge further. Gene families occur in this way, if its advantageous to have multiple specialised versions of the same protein.
How can viral DNA be incorporated into the host’s genome?
The virus inserts its DNA into the host genome, and if it leads to the host thriving in its environment, it may lead to permanent incorporation. Endogenous retrovirus is believed to originate from viral DNA.
What are selection pressures and how do they influence evolution?
Selection pressures are factors that select for a certain mutation. ie. antibiotics in culture will select for bacteria with the resistance gene. Selection pressures allow survival of the fittest to take place.
What does conservation of a sequence across different species tell us?
It tells us that the sequence is likely important because it has been strongly selected for by different organisms.
What is a SNP?
A Single Nucleotide Polymorphism is a position in a sequence where some individuals have one nucleotide and other individuals have another nucleotide. It’s a form of variation, not a mutation, but most of the time it doesn’t cause any change in phenotype. 30million SNPs with a population frequency of >0.1%. Different SNPs are common in geographical populations.
How can we use genome comparisons to improve medicine?
Diagnosing cancer - Sequencing genes from “cell free” DNA in the bloodstream and compare it to DNA in cells to see differences.
Treating AIDS - HIV virus has many different genome sequences. Antiretroviral drugs can be tailored to the virus’ sequence.
Managing genetic disease risk - GWAS find associations between SNPs (& other genome features) and disease risk
Monitoring disease outbreaks - Pathogen genomes can be sequenced to identify the origin of the outbreak
