DNA and RNA
Which base pairs with thymine in DNA?
Adenine
What is the main goal of mitosis in multicellular organisms?
Growth, tissue repair, and making identical somatic cells
Which molecule carries the DNA code from the nucleus to a ribosome?
Messenger RNA (mRNA)
Define a mutation in simple terms.
A change in the DNA sequence.
Define natural selection in one sentence.
organisms with beneficial traits survive and reproduce more, passing those traits on.
If one DNA strand reads 5'–ATG CCA–3', what is the complementary DNA strand (5' to 3')?
TAC GGT
During which phase of mitosis do sister chromatids separate?
Anaphase
Where does transcription occur and where does translation occur in a eukaryotic cell?
Transcription - Nucleus
Translation - Ribosomes
Name three possible effects a mutation can have (use simple labels: harmful, neutral, beneficial).
Harmful (disease), neutral (no effect), beneficial (gives advantage).
What is carrying capacity? Name one thing living and one thing nonliving that can make a habitat support fewer animals.
Carrying capacity is the largest number of individuals of a species that an environment can support over time.
One living (biotic) factor: predators — if more predators are present, fewer animals survive (example: more wolves reduce the deer population).
One nonliving (abiotic) factor: water availability — if drought reduces water, the habitat supports fewer animals (example: a pond drying up lowers the number of frogs it can support).
List two clear differences between DNA and RNA.
DNA: double-stranded, deoxyribose, uses T instead of U
RNA: single-stranded, ribose, uses U.
How many haploid cells are produced from one meiotic division in animals?
4 genetically variable haploid
Using the DNA template 3'–TAC GGA–5', write the mRNA sequence (5' to 3')
AUG CCU
What is a frameshift mutation and how is it different from a point mutation?
Frameshift: insertion/deletion shifts reading frame affecting many codons. Point: single base change affecting one codon.
Explain how genetic variation produced by meiosis and mutations can contribute to evolution by natural selection.
Meiosis (independent assortment, crossing-over) + mutations create variation; selection acts on variation so allele frequencies change.
State Chargaff’s rule and give an example calculation: if thymine is 35%, what percent is guanine?
If T = 35%, then A = 35%; remaining 30% is C + G, so G = 15%
Explain one key difference between anaphase of mitosis and anaphase I of meiosis using chromosome behavior.
In mitosis anaphase sister chromatids separate; in anaphase I of meiosis homologous chromosomes separate.
Give one function each for mRNA, tRNA, and rRNA.
mRNA: carries codons;
tRNA: brings specific amino acids;
rRNA: part of ribosome and helps catalyze peptide bonds.
Explain how a mutation in a gene can change a trait (trace gene → protein → trait).
Mutation → altered mRNA → different amino acid sequence → altered protein structure/function → changed trait or phenotype.
Describe one example of an adaptation and how it increases fitness in an environment.
Example: thicker fur in cold climates increases survival by retaining heat → higher reproductive success.
What is the function of telomerase and why are telomeres important during DNA replication?
Telomerase adds repeat sequences onto chromosome ends (telomeres) to prevent loss of gene sequences during replication.
What is crossing over and independent assortment and during which meiotic events do these occur?
Crossing Over - The exchange of genetic information during Prophase I
Independent Assortment - homologous chromosome pairs align randomly along the middle of cell during Metaphase I.
Describe the steps of protein synthesis from DNA to finished polypeptide, naming at least one enzyme or structure involved.
DNA unwinds → transcription by RNA polymerase makes pre-mRNA → processing (splicing, cap, tail) → mRNA to ribosome → tRNAs match codons, peptide bonds form (ribosome) → polypeptide folds into functional protein.
Describe how gene expression can be influenced by both genetic and environmental factors (e.g., same plant with different height and exposed to different light).
Genes provide potential; environment influences expression (example: same-seeded plants—one grown in low light is shorter despite same genes).
Using population-level thinking, explain how a sudden environmental change (like a drought) could change allele frequencies over several generations.
Drought favors alleles for drought-tolerance; less-fit alleles decline in frequency over generations as tolerant individuals leave more offspring.