Daimark Bennett Genetics In Evolution Flashcards
What is evolution
Change over time
Within a species - gene pool - microevolution
Type and number of species - macro evolution
Microevolution
Evolution within a species
Differences between related species
Microevolution
Longer periods of time
How and when all forms of life came to be
Organic evolution
Lamarck
Pre Darwinian
Most primitive forms of life were produced by spontaneous generation
Acquire traits by use disuse
Slowly evolved to be more complex (progressive development )
Eg a horse grows muscle mass therefore it’s offspring are larger and have more muscle
Darwin and Wallace
Origin of species
Variation in living forms in nature and domestication
Similarity between species
Descent by modification Too many individuals to survive Differential survival between individuals Gradual change in traits in population New species
Geographic variation
Genetic differences increase with distance
Isolated populations evolve down separate pathways
Spatial variation and forming species
Races - variation across space , interbreeding possible
Sub-species - geographic isolation, limited genetic differentiation
Ring species - variation , interbreeding from some populations possible
Islands
Show importance of isolation in endemicity
Artificial selection
Give a species different phenotypes by breeding select individuals of 1 character type over another
Malthus
Found the human population increasing
Humans reproducing too quickly faster than the environment can sustain - overproduction
Have to limit family size or fall victim to famine and disease
Malthus applied to Darwin
Organisms overproduce
Population is limited by predation, food, climate
Creates competition
Some individuals have advantageous traits and are better competitors
They survive and these traits are passed to offspring
Over time the species has a higher reproductive success
Conditions of Natural Selection
IF
individuals vary in character
Some of that variation is heritable
Variation differs in mean number of offspring produced
THEN
Next gem will be biased to variants that give a greater mean of offspring
Gradual accumulation of change
Hutton and Lyell
Geological processes seen today are the same as in the past
Small yearly changes over a large amount of time produce dramatic changes in geological features
Hutton applied to Darwin
Small differences in fitness between individuals create large morphological differences over time
Phenotype
Observed characteristics appearance
Genotype
Particular set of alleles that determine the genetic constitution of an organism
Allele
One of two or more forms of a particular gene
Gene
The unit of inheritance which specifies a polypeptide contributing to cell function
What determines phenotype
Genotype establishes a fixed potential and the environment decides to what potential it is reached
Enviro - language and religion
Interactional - height behaviour and weight
Mostly genetic - bloody type and eye colour
5-HTT
Gene environment interaction
5HTT is involved in the release of serotonin, if there is a mutation then too little serotonin will be released and mag cause depression
Prozac can be taken to increase serotonin release
What is the ‘normal’ phenotype
There isn’t one
In genetics we talk about the ‘wild-type’ alleles and ‘mutant’ alleles
Polymorphism
Different alleles for many genes giving natural variation
Discontinuous characters
Discrete
Eg eye colour
You either have one or the other
Continuous characters
Not discrete types eg height as many genes effect it
Where does genetic variation come from ?
Pre existing
Mutations in previous gremlins
Recombination in meiosis
Types of mutation
Substitution - transition or trans version
Duplication
Deletion
Effects of mutations
Deleterious - protein is changed meaning a loss of function
Advantageous - Increased activity of enzyme
Neutral - no observable change
Synonymous changes
Still codes for the same amino acids producing the same protein
Non synonymous change
Missense - substitute an amino acid
Nonsense - truncate the protein
Frameshift - alter every subsequent amino acid
How is variation maintained in a population
Heterozygote advantage
Each meiosis creates new mutations
Homeotic genes
Master control genes
Mutants transform one tissue type into another
Very dangerous can be lethal
Mechanisms of change
Mutation - change in dna bases
Migration - some individuals in a population join a new population and they become more present in the new population
Genetic drift - random passing of certain genes to the next generation
Natural selection - advantageous alleles
Genetic variation occurs through
Mutations - changes in dna , a single mutation can have a large effect or even no effect in most cases it is the accumulation of small changes overtime
Gene flow - any movement of genes from one population to another
Sex - can introduce new gene combinations into a population
Somatic mutations
Occur in non reproductive cells and cannot be passed into offspring
Causes of mutations
DNA fails to copy accurately and so naturally occur through mistakes in dna replication
External influences such as chemicals or radiation in the environment
Genetic drift
In each generation some individuals may by chance leave behind a few more descendants than other individuals
The genes of the next genes of lucky individuals not better individuals
Conserved sequences
Selection limits the amount of genetic variation in coding sequences
Essential sequences tend to be invariable through generations
The lack of variability is a sign that specific sequences are highly selected for
Duplicated genes
A duplicated gene can accumulate changes without being selected against
Duplication can lead to formation of multi gene families
Individual members are sufficiently different for the gene products to have distinctive properties
Role of DNA duplication
Gene duplication is evolutionary
May be facilitated by the presence of introns
Creation of new genes
Types of repeated DNA sequence
Repeated genes and pseudo genes Mostly non coding DNA Structural DNA such as telomeres and centromeres Junk DNA Parasitic DNA DNA with no specific function
Micro satellites
Short simple tandem repeats
Dinucleotides
Trinucleotides
Tetranucletides
Diploid cells
Two sets of every chromosome
Somatic cells
Haploid cells
One set of every chromosome
Gamete
Prophase
In mitosis homologous chromosomes do not pair up however in meiosis they do allowing genetic recombination
Crossing over at prophase 1
Genetic recombination between non sister chromatids at the chiasmata
Allows homologues to exchange chromosomal material
Independent assortment at metaphase 1
Homologues held together by chaismata from crossing over
Microtubules attach to each homologues
Not each sister chromatid
Pulling them to random poles
Sex is counter productive
Two fold cost of sex
Only 1 sex reproduces and gives birth and males give little parental care
Advantages of sex
Removing deleterious mutations
Spreading beneficial mutations
Variance
Mullers ratchet
Under asexual reproduction mutations can not be lost from a strain
If a population is small lose ‘zero mutation’ class
Sex can restore this
Transposable elements
LINEs
Encore reverse transcriptase
Self mobile
SINEs
Not encode reverse transcriptase is
Not self mobile but can move when LINEs move
How transposable elements effect genes
Insertion mutagenesis - can disrupt splicing
Alter gene expression
Frameshift
Has no effect if in an intron
Exon shuffling can insert copy a gene and shuffle taking the exon with it
Chromosome mutations
Deletion Duplication Inversion Centric fusion Translocation Reciprocal translocation
Inversions during meiosis
Followed by crossing over
Can be lethal as same alleles so not switch with one another and can mean homologous chromosomes cannot pair and inviable offspring is produced
Could also be advantageous and frequency would increase
Chromosomal polymorphism
Varying chromosome counts or shapes of chromosomes
Common in insects
Cline - regular chnage in allele or inversion frequencies over geographical areas
Supergenes
Inversions protect groups of alleles within them reducing the frequency of crossing over
Alleles are Locked tightly together and inherited as a single unit
Karyotype
Number size and shape of a set of chromosomes
Synteny
Changes in chromosome organisation during evolution can be traced by synteny and can contribute to speciation
Island mice separated by mountains
Became isolated it seemed no phenotypic change but hybrids were infertile
Ploidy
Variations in chromosome number
Euploid - changes in whole sets of chromosomes
Aneuploid - changes in numbers of single chromosomes
Polyploids
Polyploids tend to be larger due a larger cell size
Auto polyploids - all chromosomes derived from a single species
Allopolyploids - chromosomes come from more than one species
Autotetraploids
Chromosome doubling
A 2x genome becomes 4x
Allotetraploids
Made by hybridation
Accidental doubling
Lyger zonkey etc
