Exam 1 Flashcards
Chromosome
A structure made of a long DNA molecules with many genes.
Chromatin
The combination of DNA and protein which makes up a chromosome.
Nucleolus
The region inside the nucleus which synthesizes rRNA and creates ribosomal subunits from it.
Nucleus
Houses genetic information in eukaryotes.
Mitotic Spindles
Microtubules which invade the nuclear area to move the chromosomes.
Centrosome
A region near the nucleus which contains two centrioles.
Centrioles
9x3 ring structures of microtubules. They help organize the mitotic spindles.
Microtubules
Part of the cytoskeleton; made of tubulin dimers. Involved in the disjunction of chromosomes during cell division.
Microfilaments
Thinnest part of cytoskeleton. Involved in the formation of a cleavage furrow during cytokinesis.
Nucleioid
The region in a prokaryote which contains the singular circular chromosome.
NOR
Nucleolus organizer region; DNA which encodes for rRNA. Prokaryotes don’t have a NOR.
Intergenic DNA
DNA which does not code for a protein end product
Sister Chromatids
The two chromatids of a singular replicated (X-shaped) chromosome.
Cohesin
The material which holds the sister chromatids together.
Non-sister Chromatids
The chromatids of two replicated (X-shaped) homologous chromosomes.
G1
Gap 1: a phase of interphase where no DNA is synthesized, and where cellular activity is focused on growth. It contains unreplicated chromosomes.
Checkpoint: checks if cell is healthy enough to divide; if no, enters G0
G2
Gap 2: a phase of interphase following the S phase and preceding the M phase. The volume of the cell doubles in preparation for division. It contains replicated chromosomes, and thus twice the amount of DNA.
Checkpoint: checks to ensure DNA properly replicated
S
A phase of interphase following G1 in which DNA is replicated. Chromosomes change from I shape to X shape. It contains replicated chromosomes, and thus twice the amount of DNA.
M
The phase in which mitosis happens: prophase, prometaphase, metaphase, anaphase, telophase.
Checkpoint: before anaphase, checks to see if chromosomes properly aligned on plate
Centromere
The location where sister chromatids join. Its position determines the chromosome’s appearance.
A single centromere is a requirement for accurate segregation of chromosomes.
Chromosomes are counted by functional centromere.
Metacentric
Centromere in the middle
Submetacentric
Centromere slightly above middle
Acrocentric
Centromere approaching end
Telocentric
Centromere at end
P arm
Small arm of chromosome, “petite”
Q arm
Large arm of chromosome
Somatic cell
Cell of the body. All somatic cells have 2n and undergo mitosis.
Germline cell
Cell which produces gametes via meiosis.
Homologous chromosomes
Two chromosomes which exist in pairs with respect to arm lengths and centromere placements. They possess the same loci, but different alleles.
Biparental inheritance
A diploid organism receives one half of a homologous pair of chromosomes from either parent. Therefore, it receives two copies of every gene.
Interphase
The phase of the cell cycle during which mitosis is not happening.
Autosomes
Non-sex chromosomes.
Cyclin-dependent kinase
An enzyme which phosphorylates proteins involved in the cell cycle; inactive without cyclin.
Controls the cell cycle and its checkpoints.
Cyclin
The cofactor to kinase; its levels fluctuate in time with the cell cycle.
Karyokinesis
The division of genetic material.
Cytokinesis
The division of cytoplasm.
In animals: microfilaments constrict membrane, pinching it into a furrow
In plants: Cell plate is synthesized, partitioning cell
Mitosis
The asexual division of cells into daughter cells; basis of growth and repair; involves the equal distribution of chromosomes and cytoplasm.
Prophase
- chromosomes begin to condense
- nuclear envelope breaks down
- spindle fibers begin to form, centrosomes begin to move
Anaphase
- shugoshin degraded & centromere cohesin cleaved
- centromeres split (disjunction)
- daughter chromosomes begin movement to poles
Metaphase
- chromosomes maximally condensed
- separase degrades cohesin everywhere but centromere
- centromeres align on metaphase plate
Telophase
- daughter chromosomes arrive at poles
- daughter nuclei begin to form
- cytokinesis begins
Prometaphase
- centrosomes reach poles
- spindle fibers attach
Meiosis
2n to n, then n to n; results in haploidy, done by germline cells to produce gametes
Prophase I
- chromosomes begin to condense
- nuclear envelope breaks down
- spindle fibers begin to form; centrosome moves towards opposite ends
- Chromomeres form; homologs are bivalents
- synapsis, tetrad and SC formed
- crossing over
- SC degraded, attached at chiasmata
- spindle fibers attach
Metaphase I
- cohesin degraded (not at centromeres)
- tetrads move to metaphase plate with random alignment
Anaphase I
- disjunction
- dyads move to poles
Telophase I
- nuclear membrane forms around dyads
- cytokinesis
Metaphase II
- centromeres positioned along metaphase plate
Anaphase II
- centromere cohesin degraded
- dyads split apart to form monads
- monads pulled to opposite poles
Telophase II
- one monad at each pole for every dyad
- cytokinesis occurs
Meiosis I
2n to n; tetrads pulled apart, dyads sorted
Meiosis II
n to n; dyads pulled apart, monads sorted
Shugoshin
A protein which protects cohesin at the centromere from degrading prior to anaphase.
Telomere
Junk DNA ends of a chromosome.
Separase
The enzyme which cleaves cohesin.
Disjunction
The splitting of tetrads, dyads, and chromatids
Cleavage furrow
The constriction in cytokinesis caused by microfilaments.
Kinetochore
A location on the centromere to which microtubules attach.
Chiasmata
The sites of crossing over. They promote attachment but are broken in anaphase I.
Chromomere
Small beads on chromosomes representing condensed regions.
Serve as markers for homologs to know they’re homologs, allowing ‘rough pairing’ and ultimately the formation of bivalents.
Crossing over
The exchange of genetic information between two non-sister chromatids of a tetrad during prophase I.
The sites of crossing over are known as chiasmata. They are broken in anaphase I.
Synapsis
Homologs in a bivalent make contact and form a tetrad, attached at a synaptonemal complex
Bivalents
One pair of homologs which have undergone rough pairing.
Rough pairing
Due to chromomeres, distance between homologs closes, and a bivalent is formed
Tetrad
Two replicated homologs attached to each other by a synaptonemal complex
Synaptonemal complex
A protein complex which holds the tetrad together.
Disjunction
The splitting of a tetrad.
Dyad
An X-shaped chromosome which has undergone meiosis I.
Monad
An unreplicated chromosome which has undergone meiosis II.
Independent assortment
MENDEL:
Which member of a pair of unit factors a gamete receives doesn’t depend on what occurred in other pairs.
MODERNLY:
Homologs line up in metaphase I randomly, allowing for production of gametes with many different assortments of chromosomes
Spermatogenesis
The process of creating spermatozoa from a spermatogonium
MEIOSIS I:
Primary spermatocyte to 2 secondary spermatocytes
MEIOSIS II:
secondary spermatocytes to 2 spermatids
differentiation into spermatozoa
Oogenesis
The process of creating an ovum from an oogonium. The daughter cells don’t contain equal amounts of cytoplasm, and those containing less, the polar bodies, do not divide further.
MEIOSIS I:
Primary oocyte splits into secondary oocyte and first polar body
MEIOSIS II:
Secondary oocyte splits into ootid and second polar body
differentiation into ovum
Spermatogonium
Undifferentiated diploid germ cell destined to become spermatozoa; grows into primary spermatocyte
Oogonium
Undifferentiated diploid germ cell destined to become an ovum; grows into the primary oocyte
Primary oocyte
In meiosis I, splits into the secondary oocyte (receives most of the cytoplasm) and the first polar body
First polar body
A smaller haploid cell split off from the primary oocyte in meiosis I
Secondary oocyte
A larger haploid cell split off from the primary oocyte in meiosis I
Ootid
A larger haploid cell split off from the secondary oocyte in meiosis II. It differentiates into an ovum.
Second polar body
A smaller haploid cell split off from the secondary oocyte in meiosis II.
Spermatids
The haploid daughter cells of a secondary spermatocyte which has undergone meiosis II. They differentiate into spermatozoa.
True breeding
Produces identical organism when self-fertilized; fully homozygous
F1 generation
all identical heterozygous phenotype; self-fertilized to produce F2
P1 generation
two true-breeding individuals
F2 generation
member of F1 is selfed to produce F2; reveals recessive traits
Reciprocal cross
The female’s genotype is as present as the male’s genotype in two crosses across alternating genders (for hermaphroditic plants)
Unit factors
particulate causes of different traits; come in pairs in complete organisms, but only one is passed down; two are received from each parent. equivalent of genes/alleles
Characters
heritable features with variations; category of phenotypes
Traits
different versions of the character; phenotypes
Test cross
A cross done to determine the genotype of an organism with a dominant phenotype
D- * dd
Mendel’s Law of Segregation
During gamete formation, paired unit factors separate randomly
Each gamete receives one or the other with equal likelihood.
In modern terms, the chromosome the allele is on will end up in any meiotic daughter with equal likelihood.
Product law
The probability of independent events occurring simultaneously = product of all individual probabilities
Independent events
what happened in the past has nothing to do with future outcomes
Sum law
two events may happen; this is the chance either of them do
probability of either events A or B happening = prob(A) + prob(B)
Chance deviation
fluctuation from expected hypothetical ratio
impact decreased as # events increases
Null hypothesis
What is created when we assume genetic data will fit into a given ratio
Assumes no difference between measured and predicted values, and that any difference can be attributed to chance
Never fully accepted, just not rejected
Chi square analysis formula
sigma ((o-e)^2 / e)
Mendel’s Four Postulates
- Dominance/recessiveness
- Unit factors are paired
- Segregation
- Independent Assortment
Prophase II
- condensation begins
- spindle fibers form
- spindle fibers attach
Chi-sqaure o
observed value
Chi-square e
expected value
based on total number of offspring; apply expected ratio through multiplication
i.e, 150 total, 3:1 expected
3/4 * 150 = 112.5 dom
Probability value (p)
p cutoff is usually at 5% or .05
p<0.05, rejected hypothesis
Degree of Freedom
df = n-1, where n = # of possible outcomes
for 3:1, n=2, so df=1
Critical chi-square
the cutoff
if chi square < (less than) chi square critical, accepted null hypothesis
