Term
Packaging of DNA in chromosomes Chromosomes have a highly ordered structure, with
multiple levels of organization.
• The first level is a _____: a central core of 2
molecules of each:______
around which a double helical DNA is wound in_______. Adjacent nucleosomes are connected
by a segment of ________. |
|
Definition
-nucleosome
-histones H2A, H2B, H3 and H4,
-2 turns (146 bp)
-linker DNA. |
|
|
Term
Chromatin Fiber: ____ form a coiled
structure of ________.
• Further compaction occurs during cell division, when
the chromatin fiber loops around a ______ made up of _______ proteins, including _______. |
|
Definition
-Nucleosomes, 30 nm diameter.
-central scaffold
-nonhistone acidic
-topoisomerase II |
|
|
Term
Higher level packaging models
level 1- |
|
Definition
| Double helix wrapped around 4 H proteins. Linker DNA double wrapped and H1 holding it together. |
|
|
Term
| Higher level packaging models- Level 2 |
|
Definition
| Non histone scaffold proteins like the center of the flower, and loops have non scaffold proteins. The loops are loop chromatins. |
|
|
Term
| Higher level packaging level 3- |
|
Definition
| Additional non-histone scaffolding components are like the center of the flower. The rosettes are compressed into a compact bundle. The interphase chromatin are the loops, and the metaphase chromosomes look like many flowers together. |
|
|
Term
Chromatin
Two broad classes of chromatin:
– Euchromatin: |
|
Definition
Majority chromatin is in its extended
(decondensed) state during interphase, only condenses
during mitosis. |
|
|
Term
|
Definition
Remains highly condensed even in
interphase. Accounts for the dark staining regions seen
in interphase chromatin. |
|
|
Term
Heterochromatin is further
classified as:
Constitutive:
• Facultative: |
|
Definition
-always inactive and condensed: e.g. repetitive
DNA, centromeric DNA.
-can exist in both forms. E.g.: Female X
chromosome in mammals. |
|
|
Term
| Condensation during mitosis |
|
Definition
| Occurs as mitosis begins. Decondensation occurs as cell returns to interphase |
|
|
Term
| Three types of chromosomes |
|
Definition
Metacentric, submetacentric and acrocentric
chromosomes. |
|
|
Term
|
Definition
G-bands are the regions staining dark with
Giemsa stain, and are usually more condensed than the
light staining (G-negative) regions (resembling
heterochromatin). |
|
|
Term
|
Definition
Reverse banding, heating chromosomes
before staining causes AT-rich regions to denature, so
GC-rich regions stain darker: they are the less
condensed regions (active genes) that stain lightly with
G-banding |
|
|
Term
Cytogenic Banding Nomenclature
p-arm-
q-arm- |
|
Definition
Petite arm, small one on top.
Queue arm, longer bottom one. |
|
|
Term
p-telomere-
Centromere
q-telomere- |
|
Definition
|
|
Term
| Chromosome 3 on p arm, middle section, bottom. |
|
Definition
|
|
Term
| Variations in Chromosome Structure: |
|
Definition
– Deletion
– Duplication
– Inversion
– Translocation
– Transposition |
|
|
Term
|
Definition
| Removal of a section of DNA |
|
|
Term
|
Definition
| Increase in the number of copies of a chromosomal region |
|
|
Term
|
Definition
| half-circle rotation of a chromosomal region. |
|
|
Term
Translocations:
Non reciprocal- |
|
Definition
| Unequal exchanges between nonhomologous chromosomes. |
|
|
Term
Translocations
Reciprocal: |
|
Definition
| Parts of 2 non-homologous chromosomes trade places. |
|
|
Term
|
Definition
| movement of short DNA segments from one position of a genome to the other. |
|
|
Term
Variations in Chromosome Number:
Ploidy: |
|
Definition
| number of copies of a set of chromosomes. |
|
|
Term
|
Definition
variations in the number of sets of
chromosomes present within a cell. |
|
|
Term
|
Definition
monoploidy, diploidy, triploidy,
tetraploidy etc. |
|
|
Term
Aneuploidy:
– Designations: |
|
Definition
-variations in the number of an
individual type of chromosome.
-monosomy, trisomy, tetrasomy etc. |
|
|
Term
| Deletions May be caused by: |
|
Definition
– Errors in replication.
– Faulty meiotic or mitotic recombination.
– Exposure of chromosomes to DNA damaging
agents such as X rays. |
|
|
Term
|
Definition
One or a few hundred genes may be deleted.
•
May or may not be visible by banding.
•
Hemi or homozygosity for deletion may be lethal or may have minor phenotypic effect. |
|
|
Term
Deletion Heterozygotes
• Heterozygosity for a gene may be detrimental: ______
• Some rare genes require diploid content for survival:_______
Drosophila.
For some genes, deletion of one allele ______: notch gene in Drosophila |
|
Definition
-gene dosage effects.
-triplolethal (Tpl) gene in Drosophila.
-may cause
minor phenotype |
|
|
Term
Deletion Heterozygous
• Humans: deletion of a portion of chromosome 5: _____
• In humans, heterozygous deletion of more than ___of
the genome is lethal. |
|
Definition
-cri-du-chat syndrome.
-3% |
|
|
Term
|
Definition
mutation in remaining
normal allele: e.g: retinoblastoma. |
|
|
Term
Deletions reduce ______:
– formation of a deletion loop during meiosis prevents ______
– Regions flanking the ______appear closer
when mapped. |
|
Definition
-calculated map distances
-recombination in the looped section.
-deleted portion |
|
|
Term
Deletion heterozygotes can _____:
– Deletion heterozygote is...
– If the remaining allele is recessive...
– Can be used to locate positions of genes imparting... |
|
Definition
-uncover genes
-heimzygous for the gene that
is deleted.
-it’s phenotype will
be ‘uncovered’ or exhibited.
-recessive phenotypes |
|
|
Term
Duplications
• Increases the number of copies of a _____
• ___________ duplications
• ____ copies may be generated. |
|
Definition
-gene or segment of
chromosome.
-Tandem vs nontandem
-Multiple |
|
|
Term
Duplication
•Duplications May be caused by: |
|
Definition
-Breakage and faulty repair
– Unequal crossing over during recombination
– Error in replication |
|
|
Term
• Novel phenotypes:
– Increase in number of ...
– Place gene in a new environment...
• In humans, heterozygous duplication of more than______is lethal. |
|
Definition
-copies of a gene
-altering it’s expression.
- 5% of the genome |
|
|
Term
|
Definition
| -one right next to the other, in the same order, or reverse order. |
|
|
Term
|
Definition
| Not one right after the other. |
|
|
Term
X Rays break _____, then X ray breaks _______in one place.
This creates ____ duplication |
|
Definition
-one chromosome in 2 places
-homologous chromosome
-nontandem |
|
|
Term
Examples of Duplications
____ duplication in Drosophila.
• _______ (Tpl) gene duplication in
Drosophila.
• Bar eyes in Drosophila:
– Two copies cause ____; three copies
cause _____.
– Gene is on the ____
– Females homozygous for bar phenotype can
produce normal offspring: ______ |
|
Definition
-Notch gene
-Triplolethal
-bar shaped eyes
-double bar eyes
-X chromosome, region 16A
-unequal crossing over |
|
|
Term
Inversions Two types of inversions:
– Pericentric:
– Paracentric: |
|
Definition
-involving the centromere
-not involving the centromere |
|
|
Term
Inversions may be caused by:
– Two double stranded breaks introduced
– Crossovers between related sequences on the ... |
|
Definition
-by mutagens
-same chromosome in opposite orientation. |
|
|
Term
Consequences of Inversions
• Do not remove ____
• Usually normal phenotype, unless the ___
• There may be a change in expression patterns
of genes near the _____(e.g.:antennapedia gene).
• Inversion loop formation during...
• May reduce the number of... |
|
Definition
-genetic material.
-breakpoint is in the middle of a gene
-inversion breakpoints
-recombination.
-recombinant progeny. |
|
|
Term
| Heterozygous Pericentric Inversion: |
|
Definition
– One normal gamete
– One gamete with inversion
– One gamete with a duplication and deletion.
– One gamete with reciprocal duplication and deletion. |
|
|
Term
| • Heterozygous Paracentric Inversion: |
|
Definition
– One normal gamete
– One gamete with inversion
– Two deletion products
– Some material lost. |
|
|
Term
Translocations: ___
• It may or may not be associated with a _______ |
|
Definition
-when part of a chromosome
inserts into another chromosome.
-reciprocal transfer. |
|
|
Term
• Types of translocations:
-
-
– Robertsonian: |
|
Definition
– Reciprocal
– Nonreciprocal
-long arms of two acrocentric
chromosomes fuse; the two short arms are lost
resulting in one less chromosome. |
|
|
Term
Translocation
• Usually phenotypically normal;...
• If breakpoint alters promoter context, gene
regulation ________ (e.g.: ______:
t(8;14): puts the protooncogene c-myc next to the
immunoglobulin heavy chain locus, resulting in
overexpression of c-myc)
• If breakpoint occurs within a gene, the gene
function... (e.g.: CML : t(9;22): Bcr-
Abl fusion product). |
|
Definition
- no net loss or gain
of material in most cases.
-may be altered
-Burkitt Lymphoma
... may be altered |
|
|
Term
Recombination in Heterozygous
Translocations
• Heterozygous translocations can have
segregation events that lead to ...
• Formation of _____
involving four chromosomes. |
|
Definition
...unbalanced
genetic information in gametes.
-cross-like configuration |
|
|
Term
| Three types of segregations possible: |
|
Definition
– Alternate
– Adjacent I
– Adjacent II |
|
|
Term
The phenotypic consequences of varying
translocation breakpoints on a particular
chromosome can help ...
• Example: Translocation Down Syndrome. |
|
Definition
| identify the gene(s) causing a specific phenotype. |
|
|
Term
Partial trisomy 21 is sufficient to cause ____.
• Geneticists can map the minimal region of
chromosome 21 that must be in ____ to
cause the Down phenotype. |
|
Definition
-Down Syndrome
-triplicate |
|
|
Term
Transposable elements
Cytologically invisible sequence rearrangement:
movement of a segment of DNA from one location to _____.
• This may be just a transfer or a ____
• These sequences, called transposable elements, have
specific characteristics, notably the potential_______
• Example: copia in Drosophila. These sequences are
spread______, with about
30-50 copies present.
• Transposable elements are found in virtually all organisms. |
|
Definition
-another in the genome
-duplication.
- to propagate themselves.
- through out the Drosophila genome |
|
|
Term
Transposable Elements
May range from __bp __kb or more.
• May be present in ____copies.
• Drosophila has about___transposable elements, accounting for
approximately____of its genome. |
|
Definition
-50-10
-50 to 100,000
- 80 different
- 12.5% |
|
|
Term
• In humans, these elements are of two types:
– LINEs:
– SINEs: |
|
Definition
-long interspersed elements
-short interspersed elements. |
|
|
Term
Example of LINE: L1
• About ___ long sequence.
• There are about ___ copies dispersed
throughout the human genome |
|
Definition
|
|
Term
Example of SINE: Alu
• About ___ long sequence.
• There are about ____ copies dispersed
throughout the human genome.
• The human genome is about 3,000,000kb, so there
is an Alu element approximately every ...
These two elements alone comprise approximately ... |
|
Definition
-280 bp
-300,000
-10 kb.
-7% of the human genome. |
|
|
Term
Types of Transposable Elements
Retroposons: |
|
Definition
transposition via reverse
transcription of an RNA intermediate. |
|
|
Term
Types of Transposable Elements
Transposons |
|
Definition
Move/copy their DNA
directly without the requirement of an RNA
intermediate. |
|
|
Term
The DNA sequence in a retroposon codes
for a reverse transcriptase, which catalyzes ...
• Many retroposons also have other
...
• Many retroposons have a... tail. Others have _______ on either side,
these are generated because of the way the ... |
|
Definition
-the formation of DNA from an RNA
template.
-polypeptide coding sequences
- poly A
-direct repeat sequences
-DNA sequence has been inserted. |
|
|
Term
Encode an enzyme called Transposase.
• Rather than converting RNA to DNA, this
enzyme directly...
• Transposons usually have ... |
|
Definition
- removes the DNA
sequence and inserts it in another location.
-inverted repeats on either side. |
|
|
Term
Transposase excises the sequence between _____ of the genome.
• The gap created is widened by ____.
• The gap is filled in by repair enzymes that use the
_________chromosome as a
template to fill the gap.
• The template may or may not have the same
transposon; hence the transposon may be either... |
|
Definition
-the inverted
repeats and inserts it into another region
-exonucleases
-sister chromatid or homologous
... copied
or moved depending on the template sequence. |
|
|
Term
Aneuploidy
Defined-
• Autosomal aneuploidy creates a ...
• Monosomies have been reported in humans, but with
______. |
|
Definition
-The loss or gain of one or more chromosomes.
-genetic imbalance which may be lethal.
-severe abnormalities |
|
|
Term
Aneuploidy
• Trisomies of the larger human chromosomes: 1 and 2,
are _______ soon after conception.
• Some other trisomies are viable for a few years after
birth, _____.
• Most common trisomy is ____: only a small portion of extra chromosome 21 is sufficient to
manifest _______phenotype. |
|
Definition
-spontaneously aborted
-but with multiple defects
-trisomy 21
-the Down Syndrome |
|
|
Term
X-chromosome aneuploids are viable,
______.
• X-chromosome _____ compensates
for aneuploidy.
• However, there are genes on the X
chromosome that normally escape
inactivation; their dosage is disturbed in
aneuploids and hence these individuals are .... |
|
Definition
-relatively normal
-inactivation
...usually sterile |
|
|
Term
Nondisjunction is a primary cause of
aneuploidy
Meiosis I:
– two ____ and two _____ offspring.
– Homologous chromosomes... |
|
Definition
-trisomic, monosomic
...do not segregate |
|
|
Term
Nondisjunction is a primary cause of
aneuploidy
• Meiosis II:
– Two ____, one ____ and one _____
offspring.
– Sister chromatids ... |
|
Definition
-normal, trisomic, monosomic
...do not segregate normally. |
|
|
Term
Mitotic chromosome loss
•
Nondisjunction during Mitosis:
____ cells accumulate causing mosaic pattern.
•Chromosome may be lost because of failure to ....
•
E.G.: Mosaic Drosophila called ______: during the first mitotic division during embryonic development, one X chromosome is lost in one cell.
Half the fly has___ and is a female; the other half has ___ and is a male. |
|
Definition
-Trisomic and monosomic
-align properly on the microtubule spindle
-Gynandomorph
-XX, X- |
|
|
Term
Euploid cells contain ______.
•There are normally occurring or artificially propagated _____species in plants. |
|
Definition
-complete sets of chromosomes
-polyploid |
|
|
Term
To designate the number of chromosomes in a normal ____ cell, the symbol x is used. In humans, x = ___.
•
In wheat, x = 7. Hexaploid wheat strains have ___chromosomes. In their gametes, there are ___ chromosomes. |
|
Definition
|
|
Term
Monoploids have only one set of chromosomes (1x).
•
Germ cells from diploid plants are ___.
•
They can be treated with hormones to produce ______.
•
These can germinate into plants that are _________
• |
|
Definition
-haploid
-embryoids
-monoploid and sterile. |
|
|
Term
Monoploid cells can be treated with ________(e.g. ____) to make ____ cells which are fertile.
•
This is a technique used to generate __________. |
|
Definition
-microtubule blocking agents, colchicine
-diploid
-genetically engineered plants |
|
|
Term
Several plants are polyploid.
•
Edible plants are often engineered to be polyploid because they can increase ________.
•
Commercially grown peanuts, coffee, alfalfa etc are _____.
•
Strawberries are often ______.
• |
|
Definition
fruit size, crop yield
tetraploid
octaploids |
|
|
Term
______ usually are fertile because chromosome pairing is possible during gamete formation.
•
________ are usually sterile because of improper segregation of unpaired chromosomes. |
|
Definition
-Even polyploids
-Odd polyploids |
|
|
Term
Odd polyploids
These are usually sterile.
•
There is one set of chromosomes that does not have a _______.
•
Chromosomes assort randomly between the daughter cells during meiosis I to ________.
•
The larger the value of x, _____that a balanced gamete will be produced.
•
Some odd polyploids can be propagated _____________ because fertilization does not result in viable gametes. |
|
Definition
-pairing partner
-produce unbalanced gametes
-the rarer the chance
-asexually, but they do not contain seeds, |
|
|
Term
Tetraploids
May arise when diploid cells ______during mitosis.
•
When germ cells are tetraploid, the gametes are_______.
•
Polyploids where all sets of chromosomes come from the same species are called _____________.
• |
|
Definition
-fail to segregate their chromosomes
- diploid
autopolyploids |
|
|
Term
Tetraploids have evolved a mechanism to produce balanced gametes: they form ______, which are paired chromosome homologs which are _______ to the same pole during meiosis.
•
Two different alleles at a locus can give _____different genotypes, and genotypic ratio for the gametes will be ___________ |
|
Definition
-bivalents
-synapsed together and migrate
-five
-1:4:1 instead of 1:1. |
|
|
Term
Allopolyploids
Hybrid plants.
•
Hybridization between ________ results in allopolyploids.
•
E.G.: tetraploid ___ crossed to diploid ____.
•
X = 7 in wheat, a tetraploid is ___, a gamete will be __ or __.
•
X= _ in rye, diploid is __, a gamete will be____
•
The resulting hybrid plant will have ______chromosomes, and will be sterile.
• |
|
Definition
-two different species of polyploids
-wheat, rye
-28, 2x, 14
-7, 14, x = 7
-14 + 7 = 21 |
|
|
Term
Allopolyploids
Treatment with ___ during cell mitosis results in ____ the number of chromosomes, resulting in paired ____. Such a plant is called ______. |
|
Definition
-colchicine
-twice
-chromosomes
-amphidiploid |
|
|
Term
Generation of a new species: Triticale:
a hybrid of ___ _____. |
|
Definition
|
|
