Lecture 5: Mutation and Variation Flashcards
Mutation provides ____
new variation
Without variation, ____
there is nothing for natural selection to act on
What is the main structure in the machinery of inheritance?
Chromosome
Normally chromosomes are what shape?
Rod-shaped
Gene
the physical unit of heridity, composed of DNA
What do genes code for?
RNA and proteins
What are genes used interchangeably with?
Locus
Allele
alternative forms of a gene
True or False: chromosome number varies across the natural world
True
Codon
sets of three DNA bases that are translated to amino acids within protein-coding genes
Single nucleotide polymorphism (SNP)
When a single DNA base pair different causes the difference between two alleles
Exons
segments of a gene that code for amino acids
Introns
noncoding DNA segments in between the exons
Gene expression
The process by which a gene gets turned on in a cell to make RNA and proteins
Why are genotype and phenotype not necessarily linked?
phenotype can be influenced by the environment as well as genetics
Segregation
The separation of alleles during meiosis so that each gamete carries only one allele for each gene
Why is genetic segregation important?
With segregation, all alleles in a given individual have an equal chance of being inherited in the next generation
Genotype frequencies vs Allele frequencies
A1A1, A1A2, A2A2
vs.
A1, A2
What does Hardy-Weinberg Equilibrium characterize?
the distributions of genotype frequencies in populations that are not evolving
HWE is a null model, which is?
a model based on what we expect due to chance alone
p^2 + 2pq + q^2 = 1
This is the equation for finding…
Genotypic frequencies after one generation of random mating
p^2 + 2pq + q^2 = 1
p^2 = ?
2pq = ?
q^2 = ?
p^2 = frequency of homozygous genotypes (AA)
2pq = frequency of heterozygous genotypes (AB)
q^2 = frequency of homozygous genotypes (BB)
Why is p + q = 1 ?
There are only two possible alleles
What are the 5 HWE conditions?
1) mating is random
2) population size is “infinite”
3) gene flow does not occur
4) mutation does not occur
5) locus concerned is not under selection (no fitness difference between alleles)
What does deviation from HWE mean?
A locus is involved in an interesting evolutionary process
Recombination
Produces new genetic combinations within a gamete
What are two ways recombination can occur?
Independent assortment and crossing over
Crossing over
when homologous chromosomes swap segments of DNA
Recombination rate (r)
The probability that recombination occurs between a given pair of loci
If r = 1/2…
50% chance that when an individual makes a gamete that one of the chromosomes it carries will be from the mother and the other from the father
If r < 1/2…
two loci are on the same chromosome.
smaller r = closer loci
Linkage disequilibrium
alleles are found together more often than you would expect
When is linkage disequilibrium likely to occur?
when r is low
Epistasis
when the effect of an allele at one locus depends on the allele at a second locus
Horizontal vs Vertical gene transfer
HGT: the movement of DNA in organisms that reproduce asexually
VGT: the movement of DNA in organisms that reproduce sexually
Bacterial transformation
A donor bacterial cell releases DNA that is taken up by a recipient bacterial cell. This is an example of HGT.
Point mutation
single base
Which type of point mutation is usually synonymous? nonsynonymous?
Third position
Second position
Insertion/deletion
addition/removal of base(s)
Inversion
DNA segment is reversed
Fusion
two chromosomes become one
Fission
one chromosome breaks into two
Pseudogene
non-functional genes produced by stop codons
Whole genome duplication
mutation that duplicates all DNA in the genome
When does whole genome duplication occur?
when meiosis produces gametes that carry a diploid genome which then undergo fertilization
What organisms have whole genome duplications?
Common in plants
Human mutation rate
1 in 100,000,000
Which organisms prefer high mutation rates?
Viruses and parasites
Beneficial mutations
increase fitness, are rare, acted on by natural selection
Deleterious mutations
decrease fitness, more common, selected against
Pleiotropy
occurs when a single mutation affects multiple traits
Mutations in gametes vs somatic cells
Gamete: inherited
Somatic cell: not inherited, can affect bearer
Transitions vs transversions
Transitions: mutations between A and G, C and T
Transversions: all other mutations
Are transition or transversion mutations more common?
transition
Epigenetics
study of changes in expression of genes
Methylation
prevents expression of genes
Can methylated genes be inherited?
Yes
