Genetics Unit 1
YAC Vector components and their functions
- ARS: yeast origin of replication - centromere: allows for proper chromosome segragation - telomere: prevents chromosome degradation - TRP': selectable marker - foreign DNA: cloned DNA to be transferred
Level of chromatin compaction and mechanisms that cause it
- Nucleosome -> segments of DNA are wound around histone cores - 300 Angstrom fiber -> supercoiling of nucleosomes - Chromosomes in metaphase of mitosis -> loops of chromatin containing 60-100 kb of DNA are drawn together in a radial pattern by nonhistone scaffold proteins
Which features distinguish the centromeres of higher eukaryotes from yeast centromere sequences?
- bind to many microtubules - contain many more repeating units - larger
roles of the noncoding Xist RNA in X-chromosome inactivation
- coats the X chromosome that will be inactivated - recruits histone modifying enzymes to the X chromosome that will be inactivated
the RNA component of the telomerase enzyme
- complementary to the repeated sequences in telomeres - used as a template to add new repeats to the ends of telomeres
telomere sequences:
- consist of short repeated sequences - do not encode proteins
ways nucleosomes can change
- covalent modifications to the amino-terminal tails of histones - change in location
Genetic disorders that can be detected with FISH
- deletions - translocations - duplications
Chromosome centromeres are:
- essential for precise distribution of chromosomes during cell division - the sites where sister chromatids are most tightly bound together - the sites where kinetochores form, to allow spindle fiber attachment.
nonhistone proteins are responsible for:
- forming the structural background of the chromosome - regulating transcription and RNA processing - assisting with chromosome segregation - enzymatic activity in DNA replication
Autonomously replicating sequence (ARS)
- in yeast cells - contain an 11-base pair AT-rich sequence that binds to enzymes that initiate replication
Aspects of meiosis that contribute to genetic diversity
- independent assortment - crossing-over
The noncoding RNA molecule called Xist
- never leaves the nucleus - is never translated into a protein
telophase 1 of meiosis
- nuclear membrane reforms in many species - homologs have reached their respective poles
phases where two chromatids are attached at the centromere
- prophase - G2 of interphase - metaphase
Mitosis
- sister chromatids separate and move to opposite poles - kinetochores begon attaching to spindle fibers - chromosomes condense and nuclear envelope breaks down
prophase of mitosis
- the centrosomes move apart - the nucleolus becomes less visible - the chromatin condenses into more compact structures - mitotic spindle begins to form
How many origins of replication does the E. coli chromosome contain?
1
Order of nucleosome assembly
1) newly synthesized DNA is formed 2) an H3-H4 tetramer binds 3) two H2A-H2B dimers bind
observed and hypothesized levels of chromosome compaction in order from least to most compact (starting from the top)
1) nucleosome fiber or 100 angstoms 2) supercoiling to produce a 300 angstrom fiber 3) radial-loop scaffold
steps in fluoresnence in situ hybridization (FISH)
1) obtain cells in the metaphase stage of mitosis 2) drop cells on a slide and treat them with agents that cause them to burst 3) denature chromosomal DNA 4) Hybridize chromosomal DNA to single-stranded DNA probes that are tagged with a fluorescent label 5) view with a fluorescence microscope
Stages of prophase I of meiosis
1. Leptotene 2. Zygotene 3. Pachytene 4. Diplotene 5. Diakinesis
phases of mitosis
1. Prophase 2. Prometaphase 3. Metaphase 4. Anaphase 5. Telophase
in human oogenesis how many chromosomes does an oogonium carry?
46
The polarity of DNA synthesis is
5' to 3'
total number of chromatids in a human cell in the G2 phase
92
Artificial chromosome
A cloning vector that can accommodate a large DNA insert and behave like a chromosome when it is inside a living cell
Cohesin
A protein complex that holds sister chromatids together
HP1
A protein in Drosophila that binds to methylated histone H3 tails and promotes the formation of heterochromatin
inactive X chromosome
Barr body
nucleosomes with the _____ variant replacing histone H3, act as scaffolds for assembly of other proteins to form the kinetochore of higher eukaryotes
CENP-A
replicon
DNA extending from one origin of replication to the endpoints where it merges the DNA from adjoining replication forks
the absence pf nucleosomes on a specific region of DNA can be detected by:
DNase hypersensitivity of the chromatin in that region
interphase
G1, S, G2
In the chromatin of kinetochore-forming DNA of higher eukaryotes, a variant called CENP-A replaces histone
H3
X-chromosome inactivation
In some somatic cells of human females where one of the two X chromosomes is randomly turned off.
why do eukaryotic chromosomes shorten over time?
RNA primers at the 5' ends of new strands cannot be replaced by DNA nucleotides
during the cell cycle, a chromosomes consists of two chromatids attached by a centromere from the beginning of ____ until _____
S of interphase; anaphase
X inactivation center (Xic)
The 450 kb region on the X Chromosome that plays an important role in X chromosome inactivation
A diploid cell with three pairs of chromosomes has the genotype Aa Bb Cc, where each gene is on a different chromosome. If this cell were to undergo meiotic division, how many genetically different types of gametes could be produced?
The meiosis leads to formation of different kinds of gametes because of independent segregation of chromosomes during anaphase 1 and anaphase 2. The crossing over also leads to genetic variation. The number of different types of gametes can be calculated by following formula = (2) ^n Here n is the number of genes in heterozygous forms. There are three genes which are found in heterozygous form. That's why the different kind of gametes are (2) ^3= 8
remodeling complex
a modulator that uses energy from ATP hydrolysis to change the positions of nucleosomes
kinetochore
a protein-complex that is bound to the centromere, and which plays a key role in the separation of chromosomes during cell division.
position-effect variegation
a situation where heterochromatin can prevent the expression of a nearby gene in some cells but not others.
somatic cell
any cell that is not a gamete or precursor to a gamete
when nucleosomes assemble on newly-replicated DNA, the histones within each nucleosome
are a random mixture of "old" recycled histones and newly-synthesized histones.
shelterin
binds to telomeres to protect DNA sequences from degradation
G1
cells achieve majority of their growth
Meselson and Stahl relied on equilibrium density gradient centrifugation in a _______ solution to resolve the DNA containing 14N from the DNA containing 15N.
cesium chloride
facultative heterochromatin
chromatin that can interconvert between heterochromatin and euchromatin
separase
cleaves cohesin molecules found at the centromeres of sister chromatids
the additional compaction involved in converting an interphase chromosome into a metaphase chromosome is brought about by protein complexes called _____
condensins
effect of histone tail methylation on chromatin
depending on which amino acid is methylated, histone tail methylation can either open or close the chromatin
The four daughter cells produced in meiosis
each has half the number of chromosomes of the parent cell
oogenesis
egg production by female animals
affect of acetylation on lysine in core histone protein tails
eliminated the positive charge on lysine, disrupting the electrostatic attraction between the histone and the negatively charged DNA backbone
germ line
embryonic germ cells
Ovum
end product of egg formation
histone demethylases
enzyme that removes methyl groups from histone tail
telomerase
enzyme that restores sequences to extend the ends of chromosomes
histone methyltransferase (HMTases)
enzyme the adds methyl groups to a histone N-terminal tail
kinetochore microtubules
extend between a centrosome and the kinetochore of a chromatid
astral microtubules
extend from the centrosome towards the cell's periphery
result of mitosis and cytokinesis
formation of two genetically identical daughter cells
In tetrad analysis, the observation of a tetrad that is neither a parental ditype (PD), non-parental ditype (NPD) nor tetratype (t) demonstrates
gene conversion
repair of mismatched bases in heteroduplex regions leads to
gene conversion
Daughter cells produced in meiosis have
half the number of chromosomes as daughter cells produced in mitosis
diagrams of the chromosomal banding patterns produced by G-banding are called:
idiograms
which of the following are limitations of DNA polymerase?
it can only add bases to the exposed 3- end of a preexisting strand
in newly formed nucleosomes the histones:
may be unmodified initially but are accessible to modifying enzymes that, if present, can restore the parental chromatin structure.
G-banding
method for producing a reproducible pattern of dark and light bands on chromosomes by using a chemical dye
Spectral Karyotyping (SKY)
method for staining each type of human chromosome with a different color using fluorescently labeled probes
Heterochromatin regions have nucleosomes with ____ in histone H3
methyl groups attached to lysine 9 (K9)
trisomies
occur due to nondisjunction
Premeiotic germ cells that divide mitotically in females are
oogonia
polar microtubules
originate at centrosomes and interrogate near the cell's equator
Yeast research with autonomously replicating sequences (ARS), along with digestion of chromatin with DNase I, have led scientists to determine that
origins of replication are accessible regions of DNA devoid of nucleosomes
to distinguish between the portions of the chromosome on either side of the centromere, geneticists use the letter _____ to denote the shorter arm and the letter ____ to indicate the longer arm.
p; q
prometaphase
pairs of sister chromatids become attached to kinetochore microtubules which emanate from opposite poles of the cell
metaphase of mitosis
pairs of sister chromatids become organized in a single row
barrier elements
prevent the spread of heterochromatin
histone acetylation
prevents close packing of nucleosomes and therefore favors gene expression
spermatogenesis
production of sperm
shugoshin
protein that protects centromeric cohesin from cleavage during meiosis 1
euchromatin
regions of chromosomes that have less condensed chromatin
constitutive heterochromatin
regions surrounding the centromeres that remain condensed during most of the cell cycle
histone deacetylase
removes acetyl groups from histone proteins
A linear YAC with and ARS and centromere but no telomere will
replicate and segregate properly but degrade over time
satellite DNAs
short DNA sequences repeated thousands to millions of times in a tandem array
centromeres are sites where ______ are most tightly bound together
sister chromatids
order of cells in spermatogenesis
spermatogonia -> primary spermatocytes -> secondary spermatocytes -> spermatids -> sperm cells
during prophase of meiosis 1, homologous chromosomes recognize and begin to align with each other via a process called
synapsis
The step of DNA replication in which two replication forks moving in opposite directions may meet is called
termination
chromatin
the diffuse complex of DNA and proteins in a eukaryotic cell
metaphase plate
the imaginary midline between spindle poles where chromosomes line up during mitosis
in meiosis, crossing over refers to:
the physical exchange of pieces between non sister chromatids of homologous chromosomes
Heterochromatin
the tightly compacted regions of chromosomes
centrosomes
the two microtubule-organizing centers that form the mitotic spindle of animal cells
Anaphase 1 of meiosis
the two pairs of chromatids separate and move to opposite poles
The group of enzymes able to relax supercoils in DNA is called
topoisomerases
if the original mother cell had eight chromosomes, a cell in telophase of mitosis would have ___ nuclei, each with ____ chromosomes
two; eight
