Genetics Of Living Systems C19 + C20 Flashcards
Gene mutation
Random unpredictable change in DNA effecting just 1 small part of a DNA molecule
Chromosome mutation
Random unpredictable change in DNA effecting large pieces of chromosome or even the number of chromosomes present
Types of gene mutation
Substitution insertion deletion
Point mutation - substitution
When one base get replaced for another
Likely to add a different AA to polypeptide chain causing it to fold and interact differently ( tertiary and quaternary structure)
May have no effect due to genetic code being degenerate ( more than 1 codon codes for the same AA)
Different AA may have similar properties to the AA that was meant to be translated, therefore interactions may not be different
Point mutation insertion and deletion
Addition or deletion of one bass from the sequence meaning whole sequence from after that point is effected as codes are read in 3’s, each 3 is effected coding for a different AA each time
This is known as a frame shift
4 stages at which gene expression can be controlled
Transcriptional control
Post transcriptional control
Translation control
Post translation control
4 types of transcriptional control
Transcription factors
Chromatin remodelling
Methylation
Acetylation
Transcription factors (transcriptional control)
Proteins that bind to specific DNA sequences ( promoter regions)
complex of transcription factors are required for transcription to begin
By increasing/decreasing the production of specific transcription factors transcription of other genes can be controlled
Chromatin remodelling (transcriptional control)
In Eukaryotes DNA is associated with histone proteins, forming chromatin
The DNA wraps twice around a bundle of 8 histones to form a chromatin subunit structure called a nucleosome
Methylation (transcriptional control)
Addition of ME groups to DNA causes it to be more tightly packed as a result transcription factors cannot bind to the DNA and genes are not expressed
Acetylation and phosphorylation transcriptional control)
Reduce the positive charge on the histones resulting in looser packing therefore transcription factors can bind to DNA expressing genes
The lac operon ( transcriptional control) in ecoli a prokaryote
DNA strand is made up of regulatory gene, gap, promoter , operator , structural genes
DNA strand codes for lactose permease and lactase
repressor molecule binds to the promoter region stopping transcription
When lactose is present it binds to the repressor causing it to unbind from the dna allowing transcription to occur
Exon and intron
Exon - EXpressed region of DNA
intron- interagenic region ( region within the gene)
Post transcriptional control
Transcription produces a molecule called pre-mRNA which must be processed to form mature mRNA.
A cap and a tail are added, while splicing by spliceosomes removes introns
Some mRNA can also be edited through addition, deletion, or substitution
These modifications mean that a single length of DNA can produce a range of different strands of mRNA
Translation control
Degradation of mRNA - the more resistant the molecule the longer it will last in the cytoplasm, meaning a greater quantity of protein synthesis
Binding of inhibitory proteins to mRNA prevents it binding to ribosomes and the synthesis of proteins
Activation of initiation factors which aid the binding of mRNA to ribosomes
Protein kinases
Are enzymes that catalase the addition of phosphate groups to proteins
Addition of phosphate groups changes the tertiary structure and therefore the function of the protein
Many enzymes are activated by phosphorylation making protein kinases important regulators of cell activity
Protein kinases are often activated by the secondary messenger cAMP
Post translation control
Involves modification to the proteins that have been synthesised
What is morphogenesis
Regulation of the pattern of anatomical development, is controlled by a specific group of regulatory genes called homeobox genes
What are homeobox genes
ancient highly conserved regions of dna found in plants, animals and fungi that regulate morphogenesis.
Always 180 base pairs long
Code for home domains- protein segments (60 amino acids) that are transcription factors
Therefore are able to switch other genes on or off, in doing so they control the development of the body plan
Their activity is absolutely fundamental to the development of the body plan
Hox genes
Specific group of homeobox genes that are only found in animals
Responsible for positioning of body parts
Highly conserved across great evolutionary distances
Tend to exhibit co-linearity, meaning they appear along the chromosome in the order which they are expressed in the organisms
What is apoptosis
Controlled cell death which shapes different body parts by the removal of unwanted cells and tissues
Cells undergoing apoptosis can also release chemical signals which stimulate mitosis + cell proliferation leading to the remodelling of tissues
How apoptosis occurs
Cell shrinkage + dna fragmentation, nucleus condenses
Membrane blebbing and nucleus fragmentation
Apoptic bodies are broken off
Phagocytes engulf apoptic bodies
How are both mitosis and apoptosis controlled
Hox genes
What does it mean to be a pure breeding parents
Dominant dominant or recessive recessive
Homozygous
Codominance
Both alleles are expressed in the phenotype when present in the genotype
Gene locus
Location of gene on chromosome
Sex linkage
Genes whos loci are on the same sex chromosome (x and y) have different inheritance patterns from genes on the same autosomes
X chromosome is muncher larger and has more genes present on the Y therefore they are not homologous
These genes are therefore said to be sex linked as they are affected by sex
Null hypothesis
Difference between the observed value and the expected results is not statistically different, any differences are due to chance
What is chi squared used for
Used to identify whether the difference between expected and observed results is statistically different
What chromosome is haemophilia located on
X chromosome
X^H = dominant
X^h = recessive
What is an autosome
An autosome is a chromosome that isn’t a sex chromosome
Some Autosomal genes are said to be linked and will be inherited together unless split up by crossing over
The closer the 2 genes are on the autosome the less likely they are to be split up meaning they are more likely to be inherited together
Epistasis
Describes an interaction between genes are separate loci affecting a single phenotypic trait
These genes may work antagonistically or in a complimentary fashion
A gene is said to be epistatic when it’s presence modifies or surprises the effect of a gene at another locus ( the hypostatic gene)
They are sometimes referred to as modifying genes or inhibitory genes
Recessive epistasis
Presence of homozygous recessive allele at the first locus prevents the expression of another allele at a second locus
Hardy Weinberg principle
In a stable population with no disturbance allele frequency’s will remain constant from 1 generation to the next and there will be no evolution
P+Q=1
P^2 + 2PQ + Q^2 = 1
Evolution definition
A change in inherited characteristics/ allele frequency of a group of organisms over time “ decent with modification”
Events that might cause a change in allele frequency
Mutation
Genetic drift
gene flow - migration
Selection pressures
How stabilising selection
Normally occurs when environment remains unchanged
Favours intermediate phenotype
Intermediate alleles will become more prevalent ( bell curve)
Directional selection
- Typically associated with a change in environment
- positive selection of more extreme phenotypes
- moves bell curve to left or right
Disruptive selection
- can be considered as the opposite to stabilising selection
Extreme phenotype are selected for ( either direction ), birds beaks example
Average phenotypes are selected against
Genetic drift
Occurs in small populations, this is a change in allele frequency due to the random nature of mutation
An appearance of a new allele will have a greater impact in a small population then in a much larger population where there is a greater number of alleles present in the gene pool
Founder effect
Extreme genetic drift
These small populations have much smaller gene pools that original populations + display less genetic variation
Frequency of alleles that were rare will be higher in the small population
