Week 4 Flashcards
List three phenomena that can make organism phenotypes similar or different across generations without involving genetic change.
Non-genetic forms of inheritance:
(1) Cultural
(2) Maternal effects
(3) Epigenetic inheritance
Describe what evidence is needed to determine whether a trait has genetic or non-genetic inheritance.
(1) Experimental crosses: individuals with distinct phenotypes crossed to produce generations of offspring and backcross progeny.
(2) Correlations among individuals of known relatedness: strong correlation suggests genetic influence, but could be due to non-genetic similarity.
(3) Common garden experiments: rear offspring from phenotypically (and geographically) distinct parents together in a common environment. Persistent phenotypic variation suggests genetic influence.
Explain why mutations matter to evolution.
Mutations are the primary source of genetic variation.
Describe the consequences of mutations:
(1) Effects on phenotypes
(2) Effects on fitness
Phenotypic consequences of mutations can be subtle/quantitative or drastic/qualitative.
Mutations can be pleiotropic meaning a single mutation affects multiple traits.
However, most mutations are neutral or deleterious.
Mutations can be adaptive or maladaptive.
Explain whether mutations are directed or random, giving experimental evidence for this.
Mutations are random. Mutation is stochastic, not deterministic.
The Lederberg experiment:
Esther and Joshua hypothesized that antibiotic resistant strains of bacteria surviving an application of antibiotics had the resistance before their exposure to the antibiotics, not as a result of the exposure.
https://evolution.berkeley.edu/the-lederberg-experiment/
Define cultural inheritance and give an example.
Cross-generational similarity in non-genetic, behavioural traits, based on processes such as non-random imitation.
Ex) language, social norms, status (social or economic)
song dialects in white-crowned sparrows
Define maternal effects (or parental effects) and give an example.
Non-genetic effect of a mother or parental care on the phenotype of offspring, due to factors such as cytoplasmic inheritance, transmission of symbionts from mother to offspring or provisioning.
This will lead to enhanced similarity among siblings and between mothers/parents and their offspring.
Ex) Hormonally-mediated squirrel pup growth rate based on perceived food density
Define epigenetic inheritance and give an example.
Inherited changes in gene expression or phenotype that are not based on changes in DNA sequence.
Ex) Due to DNA methylation
Extensive DNA methylation produces a rare ‘mutant’ phenotype in toadflax. Resulting in radial (vs bilateral) symmetry.
Holly undergoes DNA methylation that produces a prickly leaf phenotype. This change influences plant-herbivore interactions.
https://youtu.be/MD3Fc0XOjWk
Define mutation rate and list the factors that can affect variation in mutation rate.
Number of independent origins per base pair, locus or genome per generation or per unit time.
The larger the genome, the higher the mutation rate (except viruses).
Mutation rates can be subject to selection (most environments favour low mutation rates but some favour higher mutation rates)
Name and describe four methods of estimating mutation rates.
(1) Screen offspring of genetically characterized parents over multiple generations
(2) Mutation accumulation experiments– score mutations after several generations (need to account for selection)
(3) Indirect comparison of number of fixed mutations across species (u=D/2t)
(4) Direct comparison of DNA sequence
Calculate mutation rate
μ = m/N
Mutation rate is calculated from the equation μ = m/N, where N is the average number of cells per culture (approximately equal to the number of cell divisions per culture since the initial inoculum is much smaller than N).
You add up the mutations per generation, for enough generations, then divide to get the average mutation rate per generation.
Define Hardy-Weinberg equilibrium
In a population of randomly mating individuals, allele frequencies are conserved and in equilibrium unless external forces act on them.
What are the two types of base pair substitution mutations?
Transition– purine for purine (A -G) or pyrimidine to pyrimidine (C-T)
Transversion– purine for pyrimidine
(T or C –– A or G)
Ag is pure, CT scans are not
When will mutations have an effect on the phenotype?
Mutations will have phenotypic effect if occurring in genes encoding RNA, regulatory sequences (e.g. enhancers) or protein-coding regions.
Mutations can be…
Synonymous: no effect on amino acid sequence
Non-synonymous: result in amino acid substitution
