Cell Division, Genetics, and Cell Cycle Regulation

Comprehensive practice flashcards covering cell cycle regulation, chromosome dynamics, genetics, and cell division mechanisms directly from the lecture notes.

RB normal function

Acts as a brake by holding E2F1 so the cell cannot enter S phase.

Missing or denatured RB

Results in no brake, causing the cell to divide uncontrollably and form tumors.

Hypophosphorylated RB

State where the brake is ON, actively holding E2F1.

Hyperphosphorylated RB

State where the brake is OFF, releasing E2F1 so S phase starts.

RB kinase

G1 cyclin-Cdk, which phosphorylates RB to release E2F1.

p53 function

Senses DNA damage and turns on the p21 gene.

p21 function

Blocks G1 cyclin-Cdk.

Loss of p21 binding to Cdk

RB gets phosphorylated and the cell enters S phase with damaged DNA.

p53 classification

Tumor suppressor (never an oncogene).

HER2 overexpression

Acts as an oncogene by providing too much growth signal.

G2 checkpoint

Catches incompletely replicated DNA before entry into M phase.

M (spindle) checkpoint

Monitors for unattached kinetochores; keeps the cell held in metaphase.

Kinesin directionality

Moves toward the plus end (away from the centrosome).

Dynein directionality

Moves toward the minus end (toward the centrosome / cell center).

Broken dynein phenotype

Transport toward the cell center fails and causes metaphase arrest.

Inability to tag securin with ubiquitin

Separase stays off, leaving the cell stuck in metaphase.

Inability of securin to bind separase

Separase turns on too early, causing sister chromatids to separate prematurely.

Inability of separase to cut cohesin

Sister chromatids never separate.

Rec8

A meiosis-specific cohesin (glue).

Timing problem in division

Chromatids separating too early or never, caused by defects in cohesin, securin, separase, or APC.

Movement problem in division

Inability to line up or move chromosomes, caused by defects in microtubules, kinesin, dynein, or kinetochores.

Histone lysine/arginine mutated to negative amino acids

DNA is repelled, resulting in no nucleosomes, no condensation, and no metaphase.

Condensin blocked

Chromosomes stay long and tangled, causing segregation errors.

Chromosome counting rule

Count centromeres.

Effect of DNA replication on chromosome number

No change in chromosome number; it doubles chromatids only.

$$n$$

The number of chromosomes in ONE set.

Number in front of $n$

How many copies of each chromosome type are present.

Ploidy with $6$ chromosome types per set and $3$ copies each

$n = 6$, triploid ($3n = 18$).

Haploid cell with replicated chromosomes

Could be in meiosis II (or mitosis in a haploid organism).

Human cell after telophase I

Contains $23$ chromosomes and $46$ chromatids.

Aneuploidy

Having ONE chromosome extra or missing.

Polyploidy

Having whole extra SETS of chromosomes.

Translocation and deletion

Structural abnormalities, NOT aneuploidy.

Cri du chat

A genetic condition caused by partial deletion of chromosome $5$ short arm.

Autopolyploidy

Possession of extra chromosome sets derived from ONE species.

Allopolyploidy

A hybrid of TWO species, which is then doubled.

"Same species" in polyploidy problems

Means Auto (autopolyploidy).

"Hybrid" in polyploidy problems

Means Allo (allopolyploidy).

Species A ($2n=12$ extra-set gamete) + Species B ($2n=16$ normal gamete), doubled

$12 + 8 = 20$, doubled to $40$; produces gametes with $20$ chromosomes.

Nondisjunction in meiosis I

All $4$ gametes are abnormal ($2$ are $n+1$, and $2$ are $n-1$).

Nondisjunction in meiosis II

Produces $2$ normal gametes, $1$ gamete with $n+1$, and $1$ gamete with $n-1$.

Extra chromosome from a meiosis I error

The other homolog.

Extra chromosome from a meiosis II error

An identical sister copy.

Mother with $1$ mutant chr $21$; child with trisomy $21$ and no mutation

Cannot be a maternal meiosis I nondisjunction error because MI error would transmit both maternal homologs, including the mutant.

$n+1$ sperm + normal egg

Trisomy ($2n+1$).

$n-1$ sperm + normal egg

Monosomy ($2n-1$).

Crossing over timing

Occurs during prophase I only.

Independent assortment timing

Occurs during metaphase I only.

Recombinant chromatid

A new allele combination resulting from crossing over ($Ab$ or $aB$ from $AB/ab$).

Gamete types from $AB/ab$ with one crossover

$4$ types ($AB$, $Ab$, $aB$, $ab$).

$Aa$ cell at anaphase I with no crossover

One spindle pole receives allele $A$, and the other pole receives allele $a$.

$Aa$ cell at anaphase of mitosis

Each spindle pole gets both allele $A$ and allele $a$.

Variation among one person's gametes

Crossing over + independent assortment (NOT fertilization).

Meiosis output in a diplontic animal

Gametes.

Meiosis output in a haplo-diplontic fern

Spores.

Diploid gametes

Gametes are never diploid (No).

Demonstration of the Law of Segregation

A $Tt$ heterozygote producing $50\%$ $T$ and $50\%$ $t$ gametes.

Demonstration of the Law of Independent Assortment

A dihybrid phenotypic ratio of $9:3:3:1$.

Stage of the Law of Segregation

Takes place at anaphase I.

Stage of Independent Assortment

Takes place at metaphase I.

AND rule in probability

Multiply the individual probabilities.

OR rule in probability

Add the individual probabilities.

Probability of $CC$ from $Cc \times CC$

$$1/2$$

Probability of $cc$ from $Cc \times CC$

$$0$$

Probability of $aaBbCC$ from $AaBbCc \times AaBbCC$

$$1/16$$

Probability of $BBEE$ from $BBEe \times Bbee$

$$0$$

Probability of grey ($bb$) and striped ($Ss$) from $Bbss \times BbSs$

$$1/4 \times 1/2 = 1/8$$

Probability of green and smooth from $YyRr \times YyRr$

$$3/16$$

$Rr \times rr$ cross

A test cross.

Smooth offspring of $Rr \times rr$ selfed

Produces a ratio of $3$ smooth : $1$ wrinkled.

Dominant-phenotype offspring of $Aa \times Aa$ that are $Aa$

$$2/3$$

Probability of genetically identical siblings ($2n = 12$)

$$1/64 \times 1/64 = 1/4096$$

Formula for number of gamete types

$$2^{\text{heterozygous genes}}$$

Two unaffected parents with an affected child

Indicates a recessive inheritance pattern.

Two affected parents with an unaffected child

Indicates a dominant inheritance pattern.

Carrier chance of an unaffected sibling (affected person, unaffected parents)

$$2/3$$

Number of origins of replication (ORI) in binary fission

One.

Prokaryote cytokinesis mechanism

FtsZ Z-ring forms a septum (not a cell plate).

Histones in bacterial chromosomes

No histones are present.

Consequence of blocked FtsZ

DNA copies and segregates, but no cytokinesis occurs.

Four events of cell division

Signal, replication, segregation, cytokinesis.

Polar microtubules function

Slide to push spindle poles apart.

Kinetochore microtubules function

Shorten to pull chromatids apart.

Chromatin state in telophase

Decondenses.

Source organ of erythropoietin

Kidneys.

Paclitaxel

Blocks the spindle; stops the cell cycle in M phase.

5-fluorouracil

Blocks DNA replication; stops the cell cycle in S phase.

Trastuzumab

Blocks the HER2 growth signal; stops the cell cycle in G1.

Cellular consequence of radiation

Causes DNA damage that leads to apoptosis.