Genetics & Heredity
Two heterozygous parents (Bb × Bb) for a trait where B is dominant. Give the genotypic ratio and the phenotypic ratio expected in offspring
Genotypic ratio 1 BB : 2 Bb : 1 bb. Phenotypic ratio (B dominant) = 3 dominant : 1 recessive.
Explain how a large decrease in deer population is likely to affect grass abundance and the populations of predators such as mountain lions.
Fewer deer → less grazing → grass abundance increases.
Indirect: predators may decline or shift to alternate prey
Translate mRNA AUG–AAG–UUU–GGC–UAA into its amino-acid sequence
Met–Lys–Phe–Gly–Stop
Describe what happens to a red blood cell placed in a hypertonic solution and explain why.
water exits by osmosis → cell shrinks
Explain why boiling a catalase extract before testing reduces enzyme activity and predict how this affects reaction time compared to an unboiled extract.
Boiling denatures catalase (unfolds protein) → active site lost → enzyme inactive → reaction slows and disks take longer to float.
Homozygous dominant (dark leaves) × homozygous recessive (light leaves): state the F1 genotype and expected F2 genotypic ratio after F1
F1 → all Ff (100%)
F2 from F1×F1 → 25% FF, 50% Ff, 25% ff.
Explain the difference between density-dependent and density-independent limiting factors and give one example of each.
Density-dependent factors have effects that increase with population size (like disease, predation, and competition), helping to regulate population growth naturally. Density-independent factors have effects that stay the same regardless of population size (like weather events and natural disasters), and they can cause sudden population crashes without regard to how crowded the population is. approach).
Identify the structures that are responsible for conducting the central dogma
Nuclus, DNA, RNA polymerase, DNA polymerase, mRNA, tRNA, Ribosome
Describe why the sodium–potassium pump requires ATP
It moves sodium ions (Na⁺) out of the cell and potassium ions (K⁺) into the cell against their concentration gradients.
If a cell has twice the DNA content of a G1 cell, state what cell-cycle phase it is likely in and justify your choice.
G2
Parents produce 50% black-furred and 50% brown-furred offspring (black dominant). Identify likely parental genotypes and show a Punnett square.
Most likely Bb × bb. Punnett: 50% Bb (black), 50% bb (brown).
Insect mouthpart length increased after invasive fruit appeared — explain why insects with longer mouthparts were better able to survive and reproduce with this new food source.
Insects with longer mouthparts could access the new food source and get enough nutrition to survive and reproduce. Insects with shorter mouthparts could not pierce the fruit skin, so they could not eat and died or produced fewer offspring. Over time, more insects in the population had longer mouthparts because these insects survived better and had more babies.
Explain the primary role of helicase during DNA replication and predict the immediate effect if helicase is inhibited.
Helicase unwinds DNA strands; inhibition prevents replication fork formation so replication halts.
Describe the word semi-permeable and how does relate to the cell.
Semi-permeable means that a membrane allows some substances to pass through it, but not all substances. This allows the cell membrane to protect the cell and choose which substances are allowed into the call
Compare and contrast mitosis and meiosis: list two differences in purpose and two differences in outcome (chromosome number, genetic variation).
Purpose: mitosis for growth/repair (2 identical diploid somatic cells); meiosis for gametes (4 genetically diverse haploid cells).
Differences: mitosis has one division vs. meiosis two; meiosis includes crossing over and independent assortment → genetic variation.
Describe point mutation and frameshift mutations; which one is more harmful?
Point mutations change one nucleotide, affecting only one amino acid, so the protein might still work. Frameshift mutations delete nucleotides and shift the reading frame, changing many amino acids downstream and usually destroying the protein. Frameshift mutations are more harmful because they cause widespread damage to the protein, while point mutations may have little effect.
Describe how carrying capacity and limiting factors shape population size; give one ecological example.
Carrying capacity limits populations based on resources;
example: drought reduces water → plant K declines → herbivore numbers drop.
Given an mRNA with a single-nucleotide deletion in the third codon, explain why the third, fourth, and subsequent amino acids change.
Deletion in third codon shifts reading frame so the third, fourth, etc., amino acids change; stop codon may shift altering protein length.
If you placed a cell in a hypotonic solution, what would happen to the cell and why? How would this be different from placing the cell in an isotonic solution?
In a hypotonic solution, the cell swells and may burst because water moves in by osmosis. In an isotonic solution, the cell remains unchanged because water moves equally in both directions.
If you interpret data showing maltose concentration rising quickly then decreasing in an amylase assay; name two possible explanations for the decline.
Substrate depletion, enzyme saturation, product inhibition, or enzyme denaturation
A single-nucleotide deletion near mRNA start causes a frameshift. Explain effects on downstream amino acids and translation termination
Deletion causes frameshift so downstream amino acids change; translation may encounter a premature stop, truncating the protein.
Climate change makes nectar shallower in flowers. Predict how bird beak length in the population will change over multiple generations and why.
As nectar becomes shallower, birds with shorter beaks can reach it more easily and get more food, so they survive better and have more babies. Birds with longer beaks cannot reach the shallow nectar as well, so they get less food and have fewer offspring. Over multiple generations, more birds in the population will have shorter beaks because birds with shorter beaks survive and reproduce better. The shallow nectar creates pressure that favors short beaks.
Convert mRNA AUG–AAG–UUU–GGC–UAA into the corresponding DNA template strand sequence.
mRNA AUG AAG UUU GGC UAA →
DNA template strand 5'→3': ATG AAG TTT GGC TAA.
Describe how facilitated diffusion differs from active transport in terms of energy requirement, direction of movement, and the role of carrier proteins.
Facilitated diffusion requires no ATP and moves with the concentration gradient, while active transport requires ATP and moves against the gradient; both use carrier proteins
Photosynthesis (light-dependent): Describe the main events of the light-dependent reactions, including where they occur, the role of chlorophyll, and how ATP and NADPH are produced.
Occur in thylakoid membranes of chloroplasts. Chlorophyll absorbs photons to excite electrons; water is split (photolysis) producing O2, electrons, and H+; electrons pass through an electron transport chain, pumping protons into thylakoid lumen; ATP synthase used to produce ATP (photophosphorylation); final electron acceptor NADP+ is reduced to NADPH. ATP and NADPH then fuel the Calvin cycle.