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