BIOL-3333 Genetics-Ch. 12

Describe the nucleic acid molecule(s) found in a single eukaryotic chromosome (or a chromatid if the chromosome has been replicated)?

A single, long, linear molecule of double-stranded DNA

Fruit flies inheriting at least one copy of the X-linked w+ allele will have red eyes. Expression of the w+ allele can be silenced, however, by a chromosomal rearrangement that bring it close to the heterochromatin surrounding the centromere of the chromosome; no eye pigment will be produced in such cases. The inactivation occurs randomly in some eye cells but not others. Suppose that a male fly has inherited the X chromosome shown at the tip of the figure. What ever color will this male fly have?

Solid red

In order to facilitate chromosome inactivation, Xist RNA coats the ____________ chromosome and recruits _______________ modifying enzymes

X; histone

H2B, H2A, H4, H3 are what?

histone proteins

Histone acetylation

prevents close packing of nucleosomes and therefore favors gene expression.

If a segment of chromatin is subjected to histone deacetylation, it will likely..

become more condensed, which will repress gene expression

Regions of chromosomes with highly compacted chromatin is called _______________.

heterochromatin

One hypotheses that explains the higher order of chromatin compaction proposes that the 300 angstrom fiber is folded into loops which are then gathered into rosettes and compressed at their centers. This model is know as the radial ___________________-__________________ model.

loop-scaffold

As a general rule, the less frequently a DNA segment is transcribed, the ________________________ it is compacted.

more

What affect does acetylation have on lysines in core histone protein tails?

Eliminates the positive charge on lysine, disrupting the electrostatic attraction between the histone and the negatively charged DNA backbone.

Which is the best description of an inactivated X chromosome in a somatic cell of a human female?

Facultative heterochromatin

True or false: Most, but not all, eukaryotic chromosomes contain one, double-stranded DNA molecule

False

Fruit fly eye color is usually red due to the expression of the wild type w+ allele. An inversion can bring the w+ allele into the vicinity of a heterochromatic region so the w+ expression is silenced in some cells. This situation, where eyes with red and white patches develop, is called

Position-effect variegation

Which types of sequences can be found within constitutive heterochromatin?

Transposable elements and Simple repetitive sequences (SSRs)

In order, what are the 5 steps of 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

Match the name on the left to the appropriate portion of the chromosome on the right A. p B. q C. centromere D. telomere 1. Long arm of the chromosome 2. chromosome location where kinetochore forms 3. short arm of the chromosome 4. structure at the end of a linear chromosome

A. 3 B. 1 C. 2 D. 4

What is a Barr body?

An inactivated X chromosome in mammalian somatic cells

Place these observed and hypothesized levels of chromosome compaction in order from least to most compact (starting at the top). A. Radial loop-scaffold B. nucleosome fiber of 100 angstroms C. supercoiling to produce a 300 angstrom fiber

B. C. A.

What is facultative heterochromatin?

Chromatin that can interconvert between heterochromatin and euchromatin

Chromatin is the complex of ____________________ and _____________________ found within eukaryotic chromosomes.

DNA; protein

In regions of heterochromatin, methylation of the lysine at position 9 (K9) is observed for histone

H3

In Drosophila, a protein that binds to methylated histone H3 tails and promotes the formation of heterochromatin is

HP1

The noncoding RNA molecule called Xist

Is never translated into a protein and never leaves the nucleus

DNase hypersensitivity, when DNA within chromatin can be digested by the enzyme DNase, demonstrates that the susceptible DNA sequences are

Not organized into nucleosomes

In a nucleosome, what is the nature of the chemical attraction between the histone proteins and the DNA?

The basic histone proteins are attracted to the phosphate groups along the DNA backbone.

The 450 kb region on the X chromosome that plays an important role in X chromosome inactivation is the

XIC

The gene that produces a noncoding RNA that is essential for X-chromosome inactivation is called

Xist

Which genes on the X chromosome are able to escape the effects of X chromosome inactivation in female mammalian cells?

Xist gene and Pseudoautosomal genes

N-terminal tails of histones can be chemically modified by the addition of _____________ and/or _____________groups

acetyl; methyl

DNA elements that prevent the spread of heterochromatin into regions of euchromatin are called

barrier elements

In what ways can nucleosomes change?

change in location and covalent modifications to the amino-terminal tails of histones

Nucleosomes can change in location along a DNA molecule and through ______________________ modifications on histone tails.

chemical

The additional compaction involved in converting an interphase chromosome into a metaphase chromosome is brought about by protein complexes called ____________________.

condensins

Regions surrounding the centromeres that remain condensed during most of the cell cycle are described as __________________________ heterochromatin.

constitutive

Idiograms are

diagrams of the reproducible banding patters obtained by chemical staining of chromosomes

X-chromosome inactivation persists throughout a female's life after being initiated when she is a(n)

embryo, about two weeks after fertilization

Nonhistone proteins are responsible for

enzymatic activity in DNA replication, assisting with chromosome segregation, regulating transcription and RNA processing, and forming the structural backbone of the chromosome.

Regions of chromosomes that have less condensed chromatin are called ___________________.

euchromatin

True or false: Heterochromatin is transcriptionally active.

false

True or false: Methylation of histone tails always leads to the formation of heterochromatin and repression of transcription

false

In humans with a typical constitution of chromosomes, X-chromosome inactivation induces dosage compensation by randomly inactivating one of the x chromosomes in the somatic cells of

females

A method used to identify the locations of specific DNA sequences on chromosomes displayed in a karyotype is called

fluorescent in situ hybridization (FISH)

Core ____________________ proteins contain a globular domain and a flexible amino-terminal tail. DNA wraps around the globular domains, and the amino-terminal tails protrude from the chromatin

histone

In chromatin, it is possible to detect when a gene is activated because its promoter region becomes DNase __________________.

hypersensitive

In contrast to heterochromatin, euchromatin is ________________ condensed and contains transcriptionally-_________________ genes.

less; more

Positively charged __________________ on the N-terminal tails of core histone proteins can be acetylated by histone the enzyme ___________________ _________________.

lysines; acetyl transferase

Modification of histone N-terminal tails occurs by the addition of _________________ groups to specific lysines and arginines and/or _________________ groups to specific lysines.

methyl; acetyl

An enzyme that adds methyl groups to a histone N-terminal tail is called a histone ________________________ while an enzyme that removes methyl groups is a histone _____________________

methyltransferases; demethylase

The DNA in a _______________ wraps around the core octamer of histone proteins. It takes 160 base pairs of DNA to form this structure.

nucleosome

A change in chromatin confirmation that occurs when genes are activated often involves the movement or removal of

nucleosomes

A situation where heterochromatin can prevent the expression of a nearby gene in some cells but not other is called _____________-_______________ variegation

position-effect

G-banding is a method for

producing a reproducible pattern of dark and light bands on chromosomes by using a chemical dye

of the two main types of molecule found within eukaryotic chromosomes, ___________________ are largely responsible for chromosome compaction

proteins

FISH analysis can be used to detect changes in chromosome _________________, such as deletions, duplications, or translocations

rearrangements

During gene activation, a modulator that uses the energy from ATP hydrolysis to change the positions of nucleosomes is called a

remodeling complex

Histone deacetylase is an enzyme that ______________acetyl groups from/on histone N-terminal tails.

removes

Position-effect variegation studies involving the inactivation of both the eye color and eye texture alleles on the fruit fly X chromosome have shown that heterochromatin

spreads linearly along a chromosome