Lectures 1-3 Flashcards
What are the 2 key principles/concepts of evolution
- Descent with modification ie all species have descended without interruption from an original form
- Natural Selection
It is the causal agent of adaptive evolutionary change where more offspring are produced then can survive and less well adapted individuals have a lower reproductive success than better adapted
What are the three area where evidence for evolution can be found
In fossil records which hold history and patterns of evolution
In livining organisms through comparing traits and studying their form and functions to infer evolutionary associations
Experimental evolution can be used to manipulate selection or genetic drift to test theories and predictions
Types of fossils 4
Structures
• Trace fossils – e.g. footprints, burrows, bite marks
• Chemical fossils – e.g. lipids from algae found in oils
• Unaltered remains - frozen in ice, trapped in amber
Problems of fossils
Fossilization is inherently unlikely – record is extremely incomplete due to
Biological factors such as rarity or not made of suitable fossil material
Non-biological - sediments do not always solidify into rock, and that rock must persist and the be found
Dating is can also be inaccurate
Also little about how fossilised organisms were created in the first place
Why are fossils useful
allow us to characterise timeline of life on earth and show intermeidiate or stages characteristics between different groups such as Archaeopteryx – bird-like organism but with
dinosaur features
This can be interpreted as evolutionary change
Flaw with studying evolution through living things
There is a limited ability to view evolutionary processes due to time factor
Define Macroevolution (inferred from e.g. fossil record)
Large evolutionary changes e.g. origin of new organisms, body plans
Define microevolution
Smaller-scale changes such as alterations of gene frequency within a population (e.g. changes in frequency of human
blood group types)
What does DNA stand for
DeoxyriboNucleic Acid
What is DNA
Double helix made of two polymers of nucleotides (pentose sugar + phosphate + base)
What are the 4 DNA bases and how do they
Adenine and Guanine (purines)
Cytosine and Thymine (Pyrimidines)
What are the two types of nuclear DNA
Autosomal chromosomes which are diploid, each contain two copies of each chromosome
Sex chromosomes XX and XY
Two types of cytoplasmic DNA
Mitochondria - uni parental inheritance ie it is maternally inherited in egg cytoplasm
Chloroplast uni parental inheritance maternally (in the egg) in some species, paternally inherited (in pollen) in others
Define Locus
(plural loci) is the specific location of a gene or DNA sequence on a chromosome
Define allele
One of the different forms of a gene that can exist at a single locus
Difference between heterozygote and homozygote
Heterozygote possesses two different alleles at a particular locus whilst a homo has two identical
Define linkage
The tendency for loci to be inherited together when near one another on the same chromosome as they are less likely to be separated by recombination
What is a codominant allele
When neither allele is dominant so the phenotype is a mixture of the two
What two things determines an organisms phenotype
genotype and environment
Example of pleiotropy
phenylketonuria = mutation in a single gene - reduced hair and skin pigmentation + mental retardation
Define epistasis
The effect of one gene is modified by another e.g genomic level, where one gene could code for a protein preventing transcription of the other gene or phenotypic level, the gene causing albinism would hide the gene controlling color of a person’s hair.
Which is the sense strand and which is the antisense
sense strand is coding and is transcribed
the antisense is the non coding strand
How can DNA change over time
Through mutations caused by chemicals, irradiation, viruses or occurs during replication (enzymes make a mistake)
How are mutations limited
Body has mechanisms to repair mutations using the other strand as a template
What are large scale DNA mutations
Chromosome breakages, rearrangements, duplications
What are small scale changes to DNA
Single base difference (point mutation)
Deletion/Insertion
What is transcription
Transcription is the first step in gene expression. It involves copying a gene’s DNA sequence to make an RNA molecule.
What enzyme is transcription performed by
is performed by enzymes called RNA polymerases, which link nucleotides to form an RNA strand (using a DNA strand as a template).
What is the goal of transcription
to make a messenger RNA copy of a gene’s DNA sequence
What is a non-synonymous substitution
A mutation that causes a change in an amino acid sequence
What is a synonymous substitution
A mutation that causes no change in an amino acid sequence
What is truncation
premature termination of protein elongation due to the presence of a termination codon in its structural gene as a result of a nonsense mutation.
What type of mutations are evolutionarily important
Only those passed on to the next generation are evolutionary important
How do we observe DNA variation
PCR (polymerase chain reaction)
Microsatellite genotyping
SNP chips
DNA sequencing (Sanger sequencing and next generation sequencing)
What is a micro satellite
a set of short repeated DNA sequences at a particular locus on a chromosome, which vary in number in different individuals and so can be used for genetic fingerprinting.
Example of using variation in micro-satellites to determine genetic differentiation between populations
In Lake Victoria the turbidity of the water is preventing different species of cichlid fish from recognising each others courtship dances. After comparing the variation in the populations micro satellites, those in the turbid water do not have significantly different Fst values compared to those in clear water
3 ways in which genetic variation can arise
Changes occurring during replication, or due to unrepaired DNA damage
Changes resulting from DNA repair
Acquisition of ‘new’ DNA
What type of changes can occurr during replication or due to unprepared DNA damage
Point mutation
Recombination
Duplication (of genes or chromosomes)
Chromosome rearrangements
What is a point mutation
Changes at a single nucleotide base, normally due to a mistake during DNA replication but can also be caused by exposure to x-rays, UV, certain chemicals
Types of point mutation
Substitution mutations (e.g transitions and transversions)
Insertions
Deletions
What is the the importance of redundancy in the genetic code in terms of mutations
Each AA is coded for by more than one codon so can have both synonymous changes (don’t change protein) and non synonymous changes (change protein)
Example of a point mutation
Glutamic acid changes to a valine leading to sickle cell
What causes a frameshift mutation
insertions and deletions
What diseases can be caused by frameshift mutations
cancer, Crohn’s, cystic fibrosis, HIV
What is a transition mutation
A type of substitution mutation which involves a pyrimidine to change to the other pyrimidine. Same for purine
What is a transversion mutation
A type of substitution mutation which involves a pyrimidine to change to the other purine or vice versa
