Cell cycle
During which phase of interphase does DNA replication occur?
S phase
What type of cells does meiosis produce?
Haploid gametes, such as sperm and egg cells.
What term describes the physical appearance of an organism, such as purple flowers?
Phenotype
What are the monomers, or building blocks, of DNA?
Nucleotides.
What is the flow of genetic information according to the central dogma of biology?
DNA → RNA → Protein
What are the two major processes that occur during the mitotic stage?
Explain why
Mitosis and cytokinesis
Why?
The M phase has two parts:
During which stage of meiosis do homologous chromosome pairs separate?
Anaphase I.
What law states that the two alleles for a gene separate during gamete formation, so each gamete receives only one allele?
The law of segregation
Question: Which enzyme unzips DNA by breaking the hydrogen bonds between the nitrogen bases?
Helicase.
Which enzyme attaches to DNA, unwinds it, and builds a complementary RNA strand during transcription?
Answer: RNA polymerase
A. A cell is growing and producing proteins and organelles. Which phase of interphase is it in?
B. What must happen later in interphase before the cell can divide?
A. G1 phase
B. The DNA must be replicated during S phase, followed by final preparation during G2 phase.
A. What happens during crossing over?
B. How does crossing over affect the resulting gametes?
A. Nonsister chromatids of homologous chromosomes exchange pieces of DNA during prophase I.
B. This creates recombinant chromosomes with new gene combinations, making the gametes genetically different
A purple-flowered pea plant has the genotype Pp.
A. Is the plant homozygous or heterozygous?
B. What types of alleles can its gametes receive?
A. Heterozygous
B. Half of its gametes may receive P, and half may receive p.
A. What does it mean that DNA replication is semiconservative?
B. After replication, how many old and new strands are found in each DNA molecule?
A. Each original parent strand acts as a template for a new strand.
B. Each DNA molecule contains one original strand and one newly made strand.
A. What is the difference between an mRNA codon and a tRNA anticodon?
B. What tRNA anticodon would pair with the mRNA start codon AUG?
A. A codon is a three-base sequence on mRNA, while an anticodon is the complementary three-base sequence on tRNA.
B. UAC
A scientist observes that duplicated chromosomes are not being divided equally between two new cells.
A. Which cell structure is most likely malfunctioning?
B. Explain how this structure normally helps ensure that each daughter cell receives the correct chromosomes.
A. The mitotic spindle/spindle fibers
B. Spindle fibers attach to sister chromatids at their kinetochores and pull the chromatids toward opposite sides of the cell, allowing the chromosomes to be distributed equally.
A cell has a diploid chromosome number of 2n = 6.
A. How many chromosomes will each gamete contain after meiosis?
B. Why is the chromosome number reduced during meiosis?
A. Each gamete will contain 3 chromosomes.
B. Meiosis reduces the chromosome number by half so that fertilization can restore the normal diploid number instead of doubling it every generation.
Two heterozygous purple pea plants are crossed: Pp × Pp.
A. What is the expected phenotypic ratio?
B. What is the probability that an offspring will have white flowers?
A. 3 purple : 1 white
B. 25% or 1/4
A scientist prevents DNA ligase from functioning during replication.
A. Which strand would be affected the most?
B. What would happen to that strand?
A. The lagging strand.
B. The Okazaki fragments would remain separated because DNA ligase could not connect them into one continuous strand.
A mutation prevents the introns from being removed from a eukaryotic mRNA molecule.
A. Which step of gene expression has been disrupted?
B. Explain how this could affect the protein produced.
A. mRNA processing
B. The introns would remain in the mRNA, changing the codons read by the ribosome. This could produce an incorrect amino-acid sequence or a nonfunctional protein.
A cell has damaged DNA, but it ignores the checkpoint signals and continues dividing.
A. Which type of gene may have stopped functioning properly?
B. Explain how this failure could contribute to cancer.
A. A tumor suppressor gene
B. Tumor suppressor genes normally slow or stop cell division when problems are detected. When they fail, damaged cells may continue dividing uncontrollably, potentially forming a malignant tumor.
A species reproduces sexually, but crossing over and independent assortment no longer occur.
A. Would meiosis still be able to produce haploid gametes?
B. How would this change the offspring produced by the species?
A. Yes. Homologous chromosomes could still separate during meiosis I, producing haploid gametes.
B. The offspring would have much less genetic variation because chromosomes would not exchange DNA or assort into as many different maternal and paternal combinations.
Two heterozygous Labrador retrievers, BbEe × BbEe, are crossed. The B/b gene determines black or brown pigment, while ee prevents pigment from being deposited.
A. What inheritance pattern is demonstrated when one gene alters the expression of another gene?
B. Why can a Labrador with at least one dominant B allele still be yellow?
A. Epistasis
B. If the dog is ee, pigment cannot be deposited in the hair, so the dog is yellow regardless of whether it carries B or b.
A mutation prevents DNA primase from adding RNA primers.
A. What would happen to DNA polymerase?
B. Why would both the leading and lagging strands be affected?
A. DNA polymerase would not be able to begin adding DNA nucleotides because it needs a primer to attach to.
B. Both strands require primers to begin replication, although the lagging strand would be affected more because it requires many primers for its Okazaki fragments
A cell has normal DNA and successfully produces mRNA, but its tRNA molecules cannot attach to amino acids.
A. Which process would be directly affected?
B. Explain why the cell would be unable to produce a polypeptide.
A. Translation
B. tRNA normally carries specific amino acids to the ribosome and matches its anticodon with an mRNA codon. Without attached amino acids, the ribosome cannot connect amino acids with peptide bonds to build the polypeptide