Sources of Variation
This term describes the "raw material" for evolution, specifically referring to differences among individuals due to their genotypes.
Genetic Variation
You take two genetically identical samples from a single ivy plant. You grow one in a dark closet and the other on a sunny windowsill; the one in the sun grows thick, dark green leaves, while the one in the dark grows thin, pale leaves. What type of variation is responsible for the difference in leaf appearance?
Environmental variation
Original mRNA: 5' - AUG AAC UUU GGU UAA - 3'
Mutated mRNA: 5' - AUG AAG UUU GGU UAA - 3'
What specific type of point mutation has occurred?
Silent mutation
These are homologous genes that diverge within the same genome of a single species as a result of a gene duplication event.
Paralogs
Calculate the allele frequency of B for the bat population (20 BB, 50 Bb, 30 bb).
B = 0.45
While mutation creates new alleles, these three processes during sexual reproduction are responsible for most variation in each generation.
Crossing over, Independent assortment, and Random fertilization
You collect seeds from two different populations of sunflowers—one from a dry desert and one from a rainy forest—and grow them both in the exact same greenhouse with identical water and soil. Despite the shared environment, the desert-sourced sunflowers bloom much earlier than the forest-sourced ones. What type of variation does this result demonstrate?
Genetic variation
Original protein sequence: Met-Val-His-Leu-Ser-Gly
Mutated protein sequence: Met-Val-Pro-Leu-Ser-Gly
What point mutation has happened and why?
Missense
A horticulturist notices a single Primrose plant in her garden that is much larger than the others. While the normal plants have 18 chromosomes (2n = 18), this specific plant has 36 chromosomes. When she tries to cross the large plant with the normal ones, the seeds are sterile. Identify the type of mutation and why its offspring might be sterile?
Genome duplication. During meiosis, three sets of chromosomes (triploid) cannot pair up and segregate evenly, leading to non-viable gametes.
You find a new population where 100% of the individuals are heterozygous (Bb). What is the allele frequency of b?
b = 0.5
You observe a population of hydrangeas where some are blue and some are pink. If the color is due solely to soil pH, this is an example of what?
Phenotypic Plasticity
In a "common garden" experiment, Population A foxes always turn white in winter regardless of temperature, while Population B foxes only turn white if it is cold. Which population demonstrates phenotypic plasticity via a steep reaction norm?
Population B demonstrates plasticity because its phenotype changes based on environmental cues, whereas Population A’s fixed response shows its variation is purely genetic.
If the resulting protein reads just Met - STOP, what is the technical name for this mutation, and what is its most common effect on protein function?
Nonsense - nonfunctional protein
Scientists are studying a gene that controls eye development, known as PAX6. They find a version of this gene in mice and a nearly identical version in humans. Both versions perform the exact same function: triggering the formation of eyes during embryonic development. What is the relationship of these genes?
They are orthologs
In a population of 100 bats, 20 are genotype BB, 50 are Bb, and 30 are bb. What is the frequency of the BB genotype?
This enzyme can create a double-stranded DNA copy from a mature mRNA, which can then be inserted back into the genome as a duplicate gene.
Reverse transcriptase
Identical twins Jennifer and Karen both have a "fat-absorbing" gene, but only Karen becomes obese due to her diet. Explain this interaction.
Karen's phenotype is highly influenced by environmental factors.
Why are insertions and deletions (Indels) often more "evolutionarily significant" or damaging than simple substitutions?
Indels typically cause a frameshift ehich changes the entire reading frame of the sequence from the point of mutation onward completely altering every subsequent amino acid and often introducing a premature stop codon.
Researchers find that one group of sparrows always inherits a specific "package" of three traits together: aggressive behavior, bright plumage, and early nesting. Even though these genes are located far apart on the chromosome, they are never "shuffled" by crossing over. What mutation does this represent and why is crossing over inhibited?
Because the segment is flipped, it cannot properly align with a standard chromosome during meiosis. This prevents effective recombination, locking the genes together.
If a population has 50 diploid individuals, how many total alleles for a specific gene are present in the gene pool?
100 alleles
A plant has the genotype AaBb, with each gene located on a different chromosome pair. During Meiosis I, the maternal and paternal versions of these pairs can align in any orientation before being separated into different cells. Why can this plant produce "new" allele combinations in its pollen (like Ab) that were not present in its own parents?
Due to independent assortment - creating unique combinations of alleles in every gamete.
If a trait has a heritability of 1.0, what would the "Reaction Norm" look like on a graph of Trait vs. Environment?
A horizontal or flat line (no change across environments)
Why are most mutations in "junk" DNA or those that are "synonymous" considered neutral in terms of natural selection?
They do not change the phenotype or affect the fitness of the organism.
In a species of icefish, scientists discovered a gene that produces an "antifreeze" protein, allowing the fish to survive in sub-zero waters. Upon closer inspection, they found that this gene is nearly identical in sequence to an older digestive enzyme gene also present in the fish's genome. Identify the type of mutation and what type of homologous gene this might result in?
Gene duplication and it will result in a paralog.
Consider a population of bats where 51 out of 100 bats exhibit the dominant phenotype of having red spots. What is the genotypic frequency of bats who have white spots?
0.49