Cell Cycle, Mitosis, Meiosis, Genetics & Bacterial DNA Transfer

What is the cell cycle?

The ongoing set of processes by which a cell grows, prepares for division, and then divides. (p. 2)

What happens during G1?

The cell grows and carries out metabolic activity; centrioles replicate in the described animal-cell cycle. (p. 1)

What happens during S phase?

DNA is synthesized/replicated, so chromosomes are copied. (pp. 1, 10)

What happens during G2?

The cell grows and makes final preparations for division; DNA proofreading and repair occur before division. (pp. 1, 10)

What is interphase?

The period between cell divisions when the cell grows, replicates chromosomes, and assembles structures needed for division; it includes G1, S, and G2. (pp. 1, 3)

What is a chromatid?

One half of a replicated chromosome. (p. 2)

What is a centromere?

The region of a chromosome where sister chromatids are connected. (p. 2)

What are homologous chromosomes?

A pair of chromosomes that match because they carry the same genes. (p. 2)

What does diploid (2n) mean?

A cell has two sets of homologous chromosomes. (p. 2)

What does haploid (1n) mean?

A cell has one set of chromosomes. (p. 2)

What is a somatic cell?

A diploid body cell that is not involved in reproduction. (p. 2)

What is a gamete?

A haploid sex cell involved in reproduction. (p. 2)

What is the outcome of mitosis?

Two genetically identical daughter cells with the same diploid chromosome number as the parent cell. (pp. 1, 3)

What is the outcome of meiosis?

Four genetically diverse haploid cells, each with half the parent cell's chromosome number. In animals these are gametes. (pp. 1, 3-6)

What happens in prophase of mitosis?

Chromosomes condense and become visible; the spindle forms, centrioles move toward opposite ends in typical animal cells, and the nuclear membrane begins breaking down. (p. 3)

What happens in metaphase of mitosis?

Chromosomes line up at the cell's center on the metaphase plate, with sister chromatids attached to spindle microtubules. (p. 3)

What happens in anaphase of mitosis?

Sister chromatids separate at the centromere and move to opposite poles; they are then called daughter chromosomes. (p. 4)

What happens in telophase of mitosis?

Nuclear membranes begin forming around each chromosome set, chromosomes uncoil, and division of the genetic material into two nuclei is completed. (p. 4)

What is cytokinesis?

Division of the parent cell's cytoplasm to form two separate daughter cells; it usually begins during the later stages of mitosis. (p. 4)

What is crossing-over?

Exchange of genetic material between non-sister chromatids of homologous chromosomes during prophase I; it produces new combinations of maternal and paternal genetic material. (pp. 5-6)

What forms during prophase I of meiosis?

Homologous chromosomes pair to form a tetrad, a group of four chromatids; crossing-over may occur. (p. 5)

What separates during meiosis I?

Homologous chromosomes separate, while each chromosome's sister chromatids remain connected. (pp. 5-6)

What separates during meiosis II?

Sister chromatids separate at their centromeres, similar to mitosis. (p. 6)

Why is there no interphase between meiosis I and II?

No additional chromosome replication occurs between the two divisions. (p. 6)

What is nondisjunction?

Failure of chromosomes to separate properly during cell division, potentially producing gametes with extra or missing chromosomes. (p. 21)

What are trisomy and monosomy?

Trisomy means a zygote has an extra copy of a chromosome; monosomy means it has only one copy. (p. 21)

What is cancer, according to the guidebook?

A collection of diseases characterized by uncontrolled cell growth and spread to neighboring tissues; some cancer cells circulate in the bloodstream. (p. 10)

What do cell-cycle checkpoints do?

They use stop/go signals and proteins to determine whether a cell is ready to proceed to the next phase. (pp. 10-11)

What does the G1/S checkpoint assess?

Whether the cell should divide, delay division, or enter the resting stage G0; conditions such as nutrient availability matter. (p. 10)

What does the G2/M checkpoint assess?

Whether DNA was damaged or improperly copied and whether proofreading and repair allow the cell to enter mitosis. (p. 11)

What do cyclin-dependent kinases (CDKs) do?

They are enzymes that modify target proteins by transferring phosphate groups from ATP, changing the targets' shape and function. (p. 11)

What role do cyclins play?

Cyclins bind to and activate CDKs; cyclins are made and broken down at precise times to regulate cell-cycle progression. (pp. 11-12)

How can mutations contribute to cancer?

They can disrupt growth signals, bypass checkpoints, and allow cell growth and division to proceed unchecked. (p. 13)

What is an oncogene?

A mutated form of a proto-oncogene that can continually behave as though a growth signal is present. (p. 14)

What do tumor-suppressor genes do?

They produce checkpoint proteins that block cell division unless conditions are appropriate; mutations can remove these blocks. (p. 14)

What do DNA-repair genes do?

They produce proteins that identify and repair damaged DNA; disrupted repair allows mutations to accumulate. (p. 14)

What is metastasis?

Invasion of surrounding tissues or spread of cancer to other parts of the body. (p. 14)

What is transduction in bacteria?

Transfer of genetic material from one bacterial cell to another by a bacteriophage, with possible expression of the transferred genes. (pp. 17-18)

How does generalized transduction occur?

A packaging error places a piece of bacterial host DNA into a phage capsid; the DNA may be injected into another bacterium and recombine with its genome. (p. 18)

How does specialized transduction occur?

When an integrated prophage leaves the host chromosome, it may take adjacent host DNA with it; the combined DNA is then replicated and transferred. (p. 18)

What is bacterial conjugation?

A natural mechanism that transfers DNA from one bacterial cell to another and can increase bacterial adaptability. (p. 19)

What are plasmids?

Double-stranded circular pieces of DNA outside the bacterial chromosome; they can carry genes, replicate independently, and sometimes move between cells. (p. 19)

What is genotype?

An organism's genetic content, commonly represented by pairs of letters for alleles inherited from each parent. (p. 20)

What is phenotype?

An organism's outward appearance or observable traits. (p. 20)

What is an allele?

An alternative form of a gene. (pp. 20, 33)

What is Mendel's law of dominance?

An organism with at least one dominant allele for a gene expresses the dominant form; the recessive form is expressed only when no dominant allele is present. (p. 21)

What is Mendel's law of segregation?

During gamete formation, the alleles for each gene separate so each gamete carries only one allele for that gene. (p. 21)

What is Mendel's law of independent assortment?

Genes for different traits can segregate independently during gamete formation. (p. 22)

When does independent assortment apply as described in the guidebook?

It is explained using genes on separate chromosomes, whose alignment during metaphase I is random; genes on the same chromosome may be inherited together. (pp. 22-23)

What is a dominant allele?

An allele that is expressed in the phenotype when at least one copy is present in the genotype. (p. 21)

What is a recessive allele?

An allele whose trait is expressed when no dominant allele is present. (p. 21)

What is homozygous?

Having two of the same allele for a gene, such as BB or bb. (p. 26)

What is heterozygous?

Having two different alleles for a gene, such as Bb. (p. 26)

What is a Punnett square used for?

It organizes possible parental gametes and predicts possible offspring genotypes and their probabilities. (p. 24)

What are the P, F1, and F2 generations?

P is the parental generation; F1 is the offspring of the parental cross; F2 is the offspring produced by crossing F1 individuals. (p. 24)

What is a monohybrid cross?

A genetic cross involving one set of alleles/one trait. (p. 24)

What is a dihybrid cross?

A genetic cross involving two sets of alleles/two traits. (pp. 24, 28-30)

How many gamete combinations can a parent form for n heterozygous allele pairs under independent assortment?

The guidebook gives the formula 2^n. For two heterozygous pairs, 2^2 = 4 possible gametes. (p. 23)

What gametes can a PpSs parent produce under independent assortment?

PS, Ps, pS, and ps. (p. 23)

What phenotype ratio is expected from a typical heterozygote × heterozygote monohybrid cross with complete dominance?

Three offspring with the dominant phenotype to one with the recessive phenotype (3:1). (p. 27)

What phenotype ratio is shown for the guidebook's F2 dihybrid plant cross?

9 purple stem/standard height : 3 purple stem/rosette-dwarf : 3 non-purple stem/standard height : 1 non-purple stem/rosette-dwarf (9:3:3:1). (p. 32)

What is a sex-linked trait?

A trait controlled by an allele on a sex chromosome. The guidebook's fruit-fly example describes white eyes as X-linked recessive. (pp. 33-34)

Why can an X-linked recessive allele be expressed in a male?

A male has one X chromosome and a Y chromosome; if the trait's allele is not represented on the Y, a recessive allele on the X is expressed. (p. 33)

In the guidebook's cross of a white-eyed female (XrXr) and red-eyed male (XRY), what are the expected F1 phenotypes?

All females have red eyes and all males have white eyes. (p. 34)

What is incomplete dominance?

The guidebook lists incomplete dominance as a classical inheritance topic, but the brief section does not provide a full definition. Review the section on p. 40. (p. 40)

What is codominance?

The guidebook covers multiple alleles and codominance in its blood-typing section; consult pp. 41-42 for the textbook's detailed explanation. (pp. 41-42)

What is a pedigree used for?

The guidebook includes pedigrees as a way to examine inheritance patterns and genetic testing. (pp. 43-48)

What is a karyotype?

An organized profile of an individual's chromosomes, typically stained, identified, and arranged in a specific order to reveal chromosome alterations. (p. 56)

What is a cytogeneticist?

A scientist who examines chromosomes and identifies alterations in a karyotype. (p. 56)

What is trisomy 21?

An extra copy of chromosome 21, associated with Down syndrome. (p. 56)

What chromosome change is associated with Edwards syndrome?

Trisomy 18. (p. 56)

What chromosome change is associated with Klinefelter syndrome?

An XXY chromosome complement. (p. 56)

What is amniocentesis?

A prenatal procedure in which amniotic fluid containing fetal cells is withdrawn so the cells' chromosomes can be examined. (p. 56)

What is recombination/crossing-over in chromosome inheritance?

Exchange of chromosomal material that can create new combinations of alleles and separate linked genes. (pp. 5-6, 23, 59-60)

What are linked genes?

Genes located on the same chromosome that may be inherited together; genes closer together are more likely to appear together in offspring. (p. 23)

How does distance between linked genes affect recombination?

The farther apart two genes are on a chromosome, the greater the chance crossing-over will separate them. (p. 23)

What is a chromosomal deletion?

Loss of a portion of chromosomal material; the guidebook associates a deletion involving chromosome 5 with cri-du-chat syndrome. (pp. 8-9, 56)

What is a chromosomal duplication?

A chromosomal segment is duplicated, creating an extra copy of that segment. (p. 9)

What is a chromosomal inversion?

A segment of chromosome is reversed in orientation; the guidebook illustrates gene order ABCD becoming ACBD. (p. 9)

What is a null hypothesis in the guidebook's chi-square example?

The hypothesis that there is no significant difference between the compared groups' proportions. (p. 70)

What is the chi-square equation?

χ² = Σ (observed − expected)² / expected. (p. 70)

What does a chi-square test compare?

Observed values with expected values to evaluate whether the data support the null hypothesis. (p. 70)

How are expected values calculated in the guidebook's two-generation example?

Combine both generations to calculate each category's proportion, then multiply each generation's total by the relevant proportion. (p. 70)

Why are bacteria useful in genetics studies?

They can transfer DNA and antibiotic-resistance genes; the guidebook uses bacterial growth on media with antibiotics to investigate resistance and transfer. (pp. 19, 76-78)

What is antibiotic sensitivity testing used to observe?

Whether bacterial strains grow in the presence of particular antibiotics, revealing resistance or sensitivity. (p. 19; pp. 76-78)

Why is Drosophila useful as a model organism?

Fruit flies are small, inexpensive to maintain, readily visible, safe to work with, have a generation time of about 12 days, and have four chromosomes; genomic similarities also make them useful in disease research. (p. 33)

What is scoring in a Drosophila genetics experiment?

Keeping accurate records of the traits observed in the flies. (p. 34)

What does the guidebook use genetic corn to investigate?

Mendelian inheritance, including parental and offspring crosses and expected genetic ratios. (pp. 26-27, 81-83)

What are Wisconsin Fast Plants used to study in this guidebook?

Plant life cycle and development, dihybrid genetics, and selection in plant populations. (pp. 28-32, 84-88, 153-154)

What does the guidebook describe about zebrafish?

Zebrafish are included as a model organism, with background and typical developmental stages covered on pp. 112-117. (pp. 112-117)

What does a control group or comparison help an experimenter do?

It provides a basis for comparing results; the guidebook's statistical examples compare observed data with an expected pattern or another generation. (pp. 67-75)

What is transcription?

The process of synthesizing RNA from a DNA template; the guidebook describes RNA polymerase binding at a promoter to begin mRNA synthesis. (p. 133)

What is translation?

The process in which an mRNA sequence is used to produce a protein. (pp. 12, 118-129)

What is a codon?

A sequence of three nucleotides in mRNA used with a codon chart to identify an amino acid or a stop signal. (pp. 127-129)

What is a mutation?

A change in an organism's DNA sequence. (pp. 33, 130-132)

How can a mutation affect a protein?

The guidebook notes that a single-nucleotide change can alter protein function, and larger mutations can delete or duplicate a gene. (pp. 14, 130-132)

What is a promoter?

A DNA sequence at the beginning of a gene where RNA polymerase binds to initiate mRNA synthesis. (p. 133)

What is an operon?

A group of genes regulated as a single transcriptional unit; they are transcribed as one mRNA that can be translated into multiple proteins. (p. 134)

What does the lac operon regulate?

E. coli's ability to use lactose as an energy source, including production of β-galactosidase, which breaks lactose into glucose and galactose. (pp. 133-134)

What happens to the lac operon when lactose is absent?

The lac repressor binds to the operator and blocks almost all transcription of lacZ by interfering with RNA polymerase's action at the promoter. (p. 134)