AP BIO: Unit Three Study Guide
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Binary fission: prokaryotic cell division; double the DNA, double the size, then split apart
Cell cycle: G1SG2MG1… continued
Interphase: G1 + S + G2 = 90% of the total cell cycle
Mitosis v. Meiosis (don’t worry about memorizing each phase of the cycle, just know the general process, the
purpose of each, and how they compare to one another)
Stage
Prophase
Metaphase
Anaphase
Telophase
Prophase I
Mitosis
Nucleus, nucleolus disappear; mitotic
spindle forms
Sister chromatids line up at middle
Sister chromatids are split apart
Nuclei of new cells reform; chromatin
uncoils
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Meiosis
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Each chromosome pairs with its
homolog; there is crossover
Metaphase I
Chromosome pairs align along middle
of cell, ready to be pulled away from
their partner
Anaphase I
Homologous pairs are pulled apart
Telophase I
Nuclear membrane reforms
temporarily; daughter cells are now
haploid (n)
Prophase II
Nucleus disappears, spindle
apparatus forms
Metaphase II
Sister chromatids line up single file in
the middle
Anaphase II
Sister chromatids are split apart
Telophase II
Nuclei of new cells reform; chromatin
uncoils
- Cytokinesis: physical separation of newly formed daughter cells of cell division
- Cell division control mechanisms
o Growth factors: factors that when present, promote growth, and when absent, impede growth
o Checkpoints: a cell stops growing to make sure it has the nutrients and raw materials to proceed
o Density-dependent inhibition: cell stops growing when certain density is reached – runs out of food!!!
o Cyclins and protein kinases: cyclin combines with CDK to form a structure known as MPF that pushes cell
into mitosis when enough is present.
- Haploid (n): one copy of each chromosome
- Diploid (2n): two copies of each chromosome
- Homologous chromosomes: chromosomes that are similar in shape, size, and function
- Spermatogenesis: the process of male gamete formation (four sperm from one cell).
- Oogenesis: the process of female gamete formation (one ovum from each cell).
- Sources of variation: crossover, 2n possible gametes that can be formed, random pairing of gametes
- Character: heritable feature, such as flower color
- Punnett Square: a tool to predict the outcome of a genetic cross; make sure you can do mendelian, codominant,
incompletely dominant, sex-linked, and blood typing punnett squares for the test
- Monohybrid cross: cross involving one character (Bb x Bb)  3:1 phenotype ratio
- Dihybrid cross: cross involving two different characters (BbRr x BbRr)  9:3:3:1 phenotype ratio
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Law of segregation: the two alleles for a trait separate during the formation of gametes – one to each gamete
Law of independent assortment: inheritance of one trait does not interfere with the inheritance of another trait
Law of dominance: if two opposite pure-breeding varieties (BB x bb) are crossed, all offspring resemble BB
parent
Intermediate inheritance: heterozygous (Yy) individual shows characteristics unlike either parent
o Incomplete dominance: Yy produces an intermediate phenotype between YY and yy (red snapdragons
RR x white snapdragons rr = pink snapdragons Rr)
o Codominance: both alleles express themselves fully in a Yy individual – (A blood type parent IAIA x B
blood type parent IBIB = AB blood type offspring IAIB)
Polygenic traits: traits that are affected by more than one gene (eye color, skin color)
Multiple alleles: traits that correspond to more than two alleles (A, B, AB, or O blood type caused by various
combinations of IA, IB, and i alleles)
Epistasis: a gene at one locus alters the phenotypic expression of a gene at another locus (coat color in mice is
controlled by a color gene and a pigment gene; if the pigment gene is homozygous recessive, the mouse is white
despite the color he inherited; color is essentially “turned off” by pigment gene)
Pleiotropy: a single gene has multiple effects on an organism (sickle cell anemia affects the shape of the red
blood cells which in turn affects the function of the heart, lungs, and kidneys; causes muscle pain, weakness, and
generalized fatigue; can ultimately lead to disastrous side effects such as kidney failure; the mutation of one
single gene wreaks havoc on the whole system)
Sex determination: pair 23 in humans; males are XY, females are XX
Autosomal chromosome: the chromosomes not involved in gender determination
Sex-linked traits: passed along on the X chromosome; more common in males than females (males have only
one X and the Y does not carry the trait at all); examples include hemophilia (where blood does not clot),
Duchenne’s muscular dystrophy (resulting in muscle weakness), and colorblindness
X inactiviation: one of two X chromosomes is randomly inactivated and remains coiled as a Barr body
Linked genes: genes that lie along the same chromosome and do not follow the law of independent assortment
o Crossover: a form of genetic recombination that occurs during prophase I of meiosis; the further apart
two genes are along a chromosome, the more often they will cross over
Linkage map: genetic map put together using crossover frequencies
o Can determine the relative location of a set of genes according to how often they cross over; if two
genes cross over in 20 percent of the crosses, they are 20 map units apart, etc.
Pedigree: family tree used to describe genetic relationships (see and practice examples given in class!).
Autosomal recessive disorders
o Tay-sachs: fatal, storage disease caused by malfunctioning lysososme; lipid buids up in brain causing
mental developmental delays and early death
o Cystic fibrosis: increased mucus buildup in lungs; untreated children die at a young age; one in 25
Caucasians are carriers
o Sickle cell anemia: caused by error of single amino acid; hemoglobin is less able to carry O2, and sickles
when O2 content of blood is low; one in 10 African Americans is a carrier. Heterozygous condition is
codominant and actually can protect against malaria.
o Phenylketonuria: inability to digest phenylalanine (an amino acid found in many protein food sources);
can cause mental developmental delays if not avoided in diet
Autosomal dominant disorders/conditions: Huntington disease (nervous system disease), polydactyly (extra
fingers or toes) and achondroplasia (dwarfism); controlled by a dominant form of the trait
Nondisjunction: error in which homologous chromosomes do not separate properly in meiosis
o Monosomy – missing a copy of a chromosome (ex Turner syndrome – X0)
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Trisomy – extra copy of a chromosome (ex Down syndrome – trisomy 21; Klinefelter syndrome – XXY or
XYY in males, XXX in females)
Chromosome disorders: deletion (Cri-du-Chat syndrome), inversions, duplications, and translocations
(Philadelphia Chromosome in some leukemia)
DNA: contains A and G (purines), C and T (pyrimidines), arranged in a double helix of two strands held together
by hydrogen bonds (A with T, C with G)
RNA: contains A and G (purines), C and U (pyrimidines), single stranded. There are three types: mRNA (copies a
single gene from the DNA and carries it out to the ribosome to make a protein), tRNA (carries the appropriate
amino acid to the ribosome as directed by the mRNA codon), and rRNA (makes up the ribosome)
DNA replication: occurs during S-phase, semi-conservative, new strand is BUILT from 5’ to 3’, old strand is
COPIED/READ from 3’ to 5’. Helicase unzips the double strand, DNA polymerase comes in and adds on the
nucleotides. Proofreading enzymes minimize errors.
Frameshift mutation: deletion or addition of 1-2 nucleotides in a sequence; shifts reading frame of codons
Missense mutation: substitution of wrong nucleotide into DNA (e.g. sickle cell anemia); still produces a protein,
although that protein may or may not work properly
Nonsense mutation: substitution of a wrong nucleotide into DNA that produces an early stop codon; will not
produce a full protein
Transcription: process by which mRNA is synthesized on a DNA template
RNA processing: introns (not coded) are spliced out, exons (coded) glued together and a 3’poly-A tail and a 5’ G
cap is added
Translation: process by which the mRNA specified sequence of amino acids is lined up on a ribosome for protein
synthesis
Codon: triplet of nucleotides that codes for a particular amino acid: start codon = AUG, stop codon = UGA, UAA,
or UAG
Promoter: base sequence in DNA that signals the start site for transcription of a particular gene
Repressor: protein that prevents the binding of RNA polymerase to a promoter site (stops the gene from being
transcribed)
Inducer: molecule that binds to and inactivates a repressor (turns off the repressor and therefore turns on the
gene and allows it to be transcribed)
Operator: short sequence near the promoter that assists in transcription by interacting with the transcription
factors (proteins) that transcribe the gene
Operon: the combination of a repressor and inducer to make an on/off switch for transcription. Allows for
production of genes only when needed. Remember the lac operon – lactose is the inducer, when present, the
repressor is removed and transcription of lactase (enzyme that digests lactose) is on; when lactose is absent,
transcription of lactase is off
Viruses: parasitic infectious agent unable to survive outside the host; can contain DNA or RNA; can have a viral
envelope (protective coat); NOT a cell; NOT alive
o Lytic cycle: one in which the viral DNA is actively reproducing and kills the host cell
o Lysogenic cycle: one in which the viral DNA lies dormant within the DNA of the host cell
Retrovirus: RNA virus that must carry with it reverse transcriptase to change its RNA into DNA in order to be
transcribed by the host cells (HIV is an example); mutate very quickly
Prion: virus that converts host brain proteins into misshapen proteins (mad cow disease [spongiform
encephalitis] is an example
Viroids: tiny plant virus
Phage: virus that infects bacteria
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Bacteria: prokaryotic cells; consist of one double-stranded circular DNA molecule; reproduce by binary fission,
sometimes contain a plasmid – extra circle of DNA that replicates independently of the main chromosome and
can be passed from bacteria to bacteria by conjugation with the sex pillus
Transformation: uptake of foreign DNA from the surrounding environment (something only bacteria can do, but
useful for studying gene transfer)
Transduction: movement of genes from one cell to another by phages (bacteria viruses), which are incorporated
by crossover into the new cell (used for gene transfer in genetic engineering)
Restriction enzymes: enzymes that cut DNA at particular sequences, often creating “sticky ends” that can be
recombined with DNA that has a matching sticky end
Vector: something that moves DNA from one source to another (usually a virus or plasmid)
Gel electrophoresis: technique used to separate DNA according to size (smaller pieces move faster), DNA moves
from the negative end to the positive end
Polymerase chain reaction (PCR): a method to produce large quantities of DNA sequences in a short amount of
time or from a small sample of DNA
Chi-square test: a statistical method to determine if experimental results (especially in genetics) are valid or due
to random chance. Make sure you can evaluate data using chi-square on the test!
Test Set-Up: 30 multiple choice questions and one long or two short free-response essay question that will be given to
you the night before (prompt only). Essays are 40% of the grade, so please prepare adequately. However, they must be
written in class without notes.