George Mason University Biology Multiple Choice I have a genetics quiz and it is going to be 10 questions multiple choices questions . I need to work someo

George Mason University Biology Multiple Choice I have a genetics quiz and it is going to be 10 questions multiple choices questions . I need to work someone major in biology and familiar with genetics course. ( the quiz it is only 20 minute)I have attached the lecture slides, please go over themI will start taking the test once are you ready and will copay and paste the questions here in the chat to answer.Thank you DNA Organization
in Chromosomes
CHAPTER 12
Lecture Presentation by
Dr. Cindy Malone,
California State University Northridge
Bacterial and Viral Chromosomes
Viral and Bacterial Chromosomes
Are Simple Molecules:
• Single nucleic acid molecule
• Largely devoid of associated
proteins
• Much smaller than eukaryotic
chromosomes
• Contain less genetic information
Viral Chromosomes
Viral nucleic acids:
• Either DNA or RNA, single or
double stranded
• Circular or linear molecules
• Viral genetic material is inert until
released into host cell
• Able to package long DNA into a
small volume, just like bacteria
and eukaryotic cells
• Bacteriophage DNA is 17 μM long
• Capsid is 0.1 μM wide
Electron micrograph of bacteriophage T2, which has had its DNA
released by osmotic shock
Bacterial Chromosome Structure
Bacterial chromosomes
• Circular, double-stranded DNA
compacted into nucleoid
• E. coli DNA is 1200 μm long
• E. coli are 2 μm wide
Bacteria DNA is associated with a few
DNA-binding proteins
• high % of positive-charged amino acids
• help to fold & bend DNA, compacting
Bacterial chromosomes are readily
replicated and transcribed
Electron micrograph of the bacterium Escherichia coli, which
has had its DNA released by osmotic shock
© 2015 PEARSON EDUCATION, INC.
Supercoiling
Supercoiling facilitates compaction of DNA:
Supercoiled DNA
• Closed-circular molecules
• More compact
Topoisomerases
Topoisomerases
• Enzymes that cut one or both DNA strands
• Wind or unwind helix before resealing ends
Supercoiled DNA and topoisomerases are found in
eukaryotes
Prokaryote and eukaryote DNA
• Replication and transcription create supercoils
downstream as double helix unwinds
Packing Problem
How is DNA packed into a
smaller nucleus?
• The length of a typical human
chromosome is ~34 mm
• All 46 chromosomes ~2 meters
long (6 feet)
• Nuclear diameter ~10 μm
Chromatin
DNA is organized into chromatin in eukaryotes
• At interphase, eukaryotic chromosomes uncoil and
decondense into a form called chromatin
• Chromatin has a large amount of associated protein
• During interphase, chromatin is dispersed throughout
nucleus
• During cell division, chromatin coils and condenses back
into visible chromosomes
Histones
Positively charged proteins associated with chromosomal DNA in
eukaryotes:
• Contain large amounts of the positively charged lysine and arginine
• Electrostatically bond to negatively charged phosphate
Five main types of histones:
• H1, H2A, H2B, H3, and H4
Nucleosomes
Nucleosomes:
• Section of DNA wrapped around 8 histone proteins
• Resemble beads on a string
• Are condensed several times to form intact chromatids
An electron micrograph revealing nucleosomes appearing as “beads
on a string” along chromatin strands derived from Drosophila melanogaster
© 2015 PEARSON EDUCATION, INC.
Second Level Packing
Secondary structure:
• Fiber is further packed into a
thicker, 30 nm structure
• H1 histones & nucleosomes
coil around each other
• 6-fold increase in compaction
• Observed during interphase
• 25 x 106 nucleosomes needed
per human nucleus
Mitotic Chromosomes
Tertiary structure:
• Further compaction must
occur
• The 30 nm structures are
folded into a series of looped
domains
• Coiled chromatin fibers are
then compacted into the
chromosome arms of a
chromatid
Chromatin fibers spilling out of a chicken erythrocyte, viewed using electron microscopy
© 2015 PEARSON EDUCATION, INC.
Chromatin Remodeling
To accommodate DNA-protein interactions, chromatin
structure must change
To allow replication and gene expression, chromatin must
• relax compact structure
• expose regions of DNA to regulatory proteins
• have a reversal mechanism for inactivity
Superhelix
Twists and turns of DNA superhelix
encircle histones
Principal packaging unit of DNA in
eukaryotic nucleus
Unstructured histone tails are not
packed into folded histone domains
within nucleosome
• Tails devoid of secondary structure
protrude through minor groove
• Provide a target for chemical
modification
Chemical Modifications
Chemical modifications are important to genetic function:
Acetylation
• Addition of acetyl group to positively-charged amino group
neutralizes positive charge, changing net charge of protein
• Associated with gene activation
• High levels of acetylation open-up the chromatin
Methylation
• Adds methyl groups to arginine and lysine residues in histones
Phosphorylation
• Adds phosphates groups to hydroxyl groups of amino acids serine and
histidine
All chemical modifications are reversible
Euchromatin and Heterochromatin
Euchromatin
• Uncoiled and active
• Appears unstained during interphase
Heterochromatin
Condensed areas are mostly inactive
Appears stained during interphase
Genetically inactive: lacks genes or contains repressed genes
Replicates later in S phase than euchromatin
Telomere maintains chromosome integrity
Centromere involved in chromosome movement
Euchromatin and Heterochromatin
•Euchromatin
• Uncoiled and active
• Appears unstained during interphase
•Heterochromatin
•
•
•
•
•
•
Condensed areas are mostly inactive
Appears stained during interphase
Genetically inactive: lacks genes or contains repressed genes
Replicates later in S phase than euchromatin
Telomere maintains chromosome integrity
Centromere involved in chromosome movement
Visualizing Chromosomes
To visualize chromosomes, samples are
made from blood samples or skin
biopsies:
• cells are cultured from the specimen
• dividing cells are arrested in
metaphase using colchicine, which
poisons the mitotic spindle
• nuclei are treated with stains that
show structural features of the
chromosomes
Mitotic chromosomes
Light microscopy
Scanning Electron Microscopy
Chromosome Banding
Chromosome-banding techniques:
• After particular treatments, some
reagents stain specific chromosomal
regions – or bands – more intensely than
others.
• Pattern of banding in each chromosome
is unique
• Allows similar sized chromosomes to be
identified
Chromosomes 4 & 5 and 21 & 22
C- and G-banding
Q bands: detected using quinacrine, a fluorescent intercalator.
G bands: seen after staining with Giemsa stain
R bands: seen after treatment with hot alkali before Giemsa
staining
C-banding
•
•
•
•
Mitotic chromosomes have a characteristic banding pattern
Only centromeres (heterochromatin) take up stain
Differential staining along length of each chromosome
Digestion of mitotic chromosome by enzyme
Human Karyotype
Karyotype: representation
of chromosomes aligned
in pairs:
• a photograph of all
metaphase chromosomes in
a cell
• arranged in pairs by length
and location of centromeres
• detects abnormal
chromosomal numbers and
structural abnormalities
Human Chromosome Banding
Nomenclature for human chromosome
banding:
• based on G-banding
X Chromosome
e.g. a gene found here would be Xq25
Repetitive DNA Sequences
Many repetitive DNA sequences in eukaryotes:
Repetitive DNA makes up 50% of the human genome
Several categories of repetitive DNA:
•
•
•
•
•
tandem repeats (TR)
variable number tandem repeats (VNTR)
short tandem repeats (STR)
short interspaced nuclear elements (SINEs)
long interspaced nuclear elements (SINEs)
© 2015 PEARSON EDUCATION, INC.
Figure 12-14
Satellite DNA
◦ Short, repeated sequences
◦ CACACACACACACACACACACACACACACACACACACACACACACACA
◦ Highly repetitive
◦ Makes up variable proportion of total DNA
◦ Found in heterochromatic centromeric regions of
chromosomes
◦ Not found in prokaryotes
◦ Microsatellites
◦ Ministatellites
◦ Macrosatellites
chromosome
DNA
Microsatellites
1-9 bp
Minisatellites
10-100 bp
Tandem Repeats (TR)
Macrosatellites
> 100 bp
Centromeres and Kinetochores
Centromeres:
• Separation of homologs during
mitosis and meiosis depends on
centromeres
• Are the primary constrictions
along eukaryotic chromosomes
• Highly repetitive DNA regions
Kinetochore proteins:
• Required for the attachment of
microtubules to the chromosomes
during mitosis
• Bind to repeat regions
Moderately Repetitive DNA
Moderately repetitive DNA includes:
• Variable number tandem repeats (VNTRs)
• repeating DNA sequences 15 to 100 bp long
• Minisatellites
• Microsatellites (short tandem repeats, STRs)
Microsatellites or STRs
Microsatellites or STRs (short tandem repeats)
• Tandemly repeated sequences
• Dispersed throughout genome
• Consist of di-, tri-, tetra-, and pentanucleotides
Interspersed Elements:
SINES and LINES
Short interspersed elements
(SINES) and long interspersed
elements (LINES):
Sequence architecture of
mammalian LTR and NonLTR transposable elements
• Transposable elements (TE) that
are mobile and relocate within
genome
• Most are non-functional, not
under positive selection and
accrue mutations over
evolutionary time
• Transposable elements are
grouped into two categories;
those containing a long terminal
repeat (LTR) and those without
(non-LTR)
• Dispersed throughout genome
• Constitute 1/3 of human genome
SINEs & Gene Regulation
Evolutionary tree showing the
split between primate and
rodent lineages about 90 million
years ago:
• Alu SINEs evolved in primates and
B SINEs in rodents
• Thought these elements evolved
independently in the two lineages
to play the same role in gene
regulation
Alu elements (labelled green)
make up ~ 10% of the human
genome
Pseudogenes
The vast majority of a eukaryotic genome does not encode
functional genes:
• Only a small portion of eukaryotic genome (2–10%) constitutes
protein-encoding genes
• Large number of single-copy noncoding regions: pseudogenes
DNA sequences representing evolutionary vestiges
Have undergone significant mutational alterations (insertions and
deletions)
Are not transcribed
Specialized Chromosomes
Specialized Chromosomes Reveal
Variations in the Organization of DNA
Polytene chromosomes
• Represent paired homologs
• Are unusual; not usually found in
eukaryotic cells
• Can be visualized by light microscopy
• Can be seen in nuclei of interphase cells
• Are found in various tissues: salivary,
rectal, midgut, and excretory tubules
Polytene Chromosomes
Paired Homologs
• DNA of paired homologs undergoes many rounds of replication
without strand separation or cytoplasmic division
Puff regions
• Bulges where DNA has uncoiled that are visible manifestations
of high level gene activity (transcription that produces RNA)
© 2015 PEARSON EDUCATION, INC.
Lampbrush Chromosomes
Lampbrush chromosomes:
• Large with extensive DNA
looping
• Found in most vertebrate
oocytes and spermatocytes of
some insects
• Meiotic chromosomes
• Synapsed pairs held together by
chiasmata
• Condense later in meiosis
• Loops are areas of active
transcription
Lampbrush chromosomes from amphibian oocytes
https://www.wehi.edu.au/wehi-tv/molecularvisualisations-dna
Sex Determination and
Sex Chromosomes
CHAPTER 7
Lecture Presentation by
Dr. Cindy Malone,
California State University Northridge
Sex Determination
In animals, including humans,
differentiation of sexes is
evident via phenotypic
dimorphism
Heteromorphic chromosomes
• Dissimilar
• Example: Sex chromosomes X
and Y
Sexual Differentiation
Life cycles depend on sexual differentiation:
Primary sexual differentiation
• Involves only gonads where gametes are produced
Secondary sexual differentiation
• Involves overall appearance of organism
Sexual Differentiation
Unisexual, dioecious, gonochoric:
• Have only male or female reproductive organs
Bisexual, monoecious, hermaphroditic
• Have both male and female reproductive organs
• Common in plants and animals
• Can produce egg and sperm
Chlamydomonas – Green Algae
Asexual reproduction:
• Some organisms spend most of their
life cycle in haploid phase
• Asexually producing daughter cells by
mitotic division
Isogametes:
• Under unfavorable conditions,
daughter cells function as gametes
• Two gametes fuse together during
mating
• Gametes usually morphologically
indistinguishable (isogametes)
Zea mays (Corn)
Plant life cycles alternative
between haploid gametophyte
and diploid sporophyte stages
• most plants produce
hermaphroditic flowers
• the male organs, stamens,
surround the inner female
organs, the pistils
• fertilization occurs when pollen
from the stamens reaches the
ovule within the pistil
Zea mays (Corn)
Diploid sporophyte stage
predominates:
• male and female
structures are present on
adult plant (monoecious)
• sex determination occurs
differently in different
tissues of same plant
• diecious plants, such as
cannabis & asparagus,
have separate male and
female plants
Drosophila (Fruit Flies)
Sex is determined by the ratio of X
chromosomes to the number of haploid
sets of autosomes
Ratio of X: autosomes
XXX flies
1.5
XX flies
1.0
XXY flies
1.0
XO flies
0.5
XY flies
0.5
Sex
metafemale
female
female
male
male
Suggests maleness genes are on the autosomes
and female genes are on the X chromosome
Nematode worm: C. elegans
Two sexual phenotypes:
• Males have only testes
• Hermaphrodites have both testes and
ovaries
• Less than 1 percent of offspring are
males
• Adults males mate with
hermaphrodites
Produce half male and half
hermaphrodite offspring
Sex Determination in C. elegans
Determination of maleness:
• No Y chromosome in C. elegans
• Ratio of X chromosomes to
autosomes determines male or
hermaphrodite in C. elegans
• Sex determination results from
presence of only one X
chromosome in males and two in
hermaphrodites
Protenor (Butterfly)
Mode of sex determination
in butterflies:
• XX/XO mode of sex
determination
• Depends on random distribution
of X chromosome into half of
male gametes
• Presence of two X chromosomes
in zygote results in female
offspring
• Presence of one X chromosome
results in male offspring
Homogametous v Heterogametous
Homogametous
• Producing like chromosomes
• Zygotes with two X chromosomes
• Results in female offspring
Heterogametous
• Producing unlike chromosomes
• Zygotes with one X and one Y chromosome
• Results in male offspring
Heterogametic Females
Females as heterogametic sex
• ZZ/ZW sex determination
• Females are the heterogametic (ZW) sex
• Males are the homogametic (ZZ) sex
• Example: chickens, & many species of reptiles, e.g.
snakes,
The Human Y Chromosome
Y chromosome determines maleness:
• Human karyotype
• 22 pairs of autosomal chromosomes
• 2 sex chromosomes
• One pair of chromosomes differs in males and females
• Females: XX
• Males: XY
Normal female: 46, XX
© 2015 PEARSON EDUCATION, INC.
Normal male: 46, XY
© 2015 PEARSON EDUCATION, INC.
Y Chromosome
Y chromosome and male development:
• Y chromosome has ~75 genes
• Fewer genes than X chromosome (9001400 genes)
PARs: Pseudoautosomal regions
• Present on both ends of Y chromosome
• Share homology with X chromosome
• Synapse and recombine with X during
meiosis
• Critical to segregations of X and Y
chromosomes during male gametogenesis
The remainder of the Y chromosome (95%)
does not recombine
MSY and SRY regions
MSY: Male-specific region of the Y
• Non-recombining region of Y
chromosome
SRY: Sex-determining region Y
• Located adjacent to PAR of the short
arm of Y chromosome
• Controls male development
Dosage Compensation
Dosage compensation:
• The X chromosome contains over 1,000 genes
(5% of the haploid genome) that are essential
for proper development and cell viability
• Females carry two copies of the X chromosome,
resulting in a potentially toxic double dose of Xlinked genes
• To correct this imbalance, female mammals
have evolved a unique mechanism of dosage
compensation
• Uses a process called X-chromosome
inactivation
X Chromosome Inactivation
X chromosome inactivation:
• At the 500-1000 cell stage (day 16 postfertilization in humans), each embryonic cell
randomly inactivates either the paternallyderived X or the maternally-derived X.
• About half of all female cells express the genes
from the paternally-derived X and half of the
cells express the genes from the maternallyderived X.
• Once an X chromosome has been inactivated in
a cell, it will remain inactivated in all of the
descendants of that cell.
Barr bodies (sex chromatin)
Barr body or sex chromatin:
• In females, the inactivated (transcriptionally silent) X
chromosome condenses into a compact structure
• Approx 0.5 μm in diameter and are seen in interphase
nuclei as darkly stained heterochromatin, lying next to
the inner surface of the nuclear membrane
• In normal females, Barr bodies are visible in 1-10% of
neutrophils, 50-65% of buccal epithelial cells and in over
90% of cells in amniotic membranes.
• Not all the cells will be in interphase, so Barr bodies will
not be visible in every cell.
Barr Bodies
Barr Bodies & Aneuploidy
In individuals with two or more X chromosomes,
the maximum number of Barr bodies is one less
than the number of X chromosomes (n-1)
45,X females (Turner syndrome) have 0 Barr
bodies
46,XY males have 0 Barr bodies
46,XX females have 1 Barr body per cell
47,XXY Klinefelter males have 1 Barr body per cell
47,XXX metafemales have 2 Barr bodies per cell
This is why X chromosome aneuploidy can be
tolerated; all but one of the extra X chromosomes
is inactivated
= inactivated X chromosome
Mosaicism
X chromosome inactivation is one reason
identical twin females are never truly
identical
• Females heterozygous for X-linked alleles are
phenotypic mosaics
• If a female mammal has alleles of a particular
gene on each of her two X chromosomes, then
about half of her cells will express one of the
alleles and about half the other allele, known as
mosaicism.
Calico Cats
In cats, one of several genes controlling
fur color is located on the X chromosome:
• Calico cats are heterozygotes and have
an allele for orange fur color on one X
chromosome and an allele for black fur
color on the other X chromosome
• These phenotypic mosaics have a
characteristic coat of patches of orange
and black fur
• This is why calico cats are normally
always female
X-Inactivation and Syndromes
Why does X-inactivation not affect syndromes such as
Turner or Kleinfelter?
• Chromosome inactivation not in early stages of development for cells
destined for gonadal tissue
• Not all X chromosomes forming Barr bodies are inactivated
• 15% escape inactivation
Dosage Compensation in
Drosophila
Drosophila females have two copies of X-linked genes:
• X-inactivation not observed in Drosophila
• Male X-linked genes transcribed at twice rate of females
Temperature Variations
Temperature-dependent sex determination:
• Controls sex determination in reptiles
• Three different patterns of temperature sex determination in reptiles
• Crocodiles, most turtles, and some lizards: incubation temperature of
eggs during embryonic development determines sex
• Temperature thought to play a role in steroid synthesis (estrogens &
androgens)
Chromosome Mutations:
Variation in Chromosome
Number and Arrangement
CHAPTER 8
Lecture Presentation by
Dr. Cindy Malone,
California State University Northridge
There are 23 pairs of
chromosomes in humans
22 pairs of the human chromosomes
are autosomes – chromosomes that
are the same in males and females
The last pair is the sex chromosomes,
two sex chromosomes are the basis of
sex – human males have XY, females
have XX
Karyotypying
Karyotype: representation of
chromosomes aligned in pairs.
• A photograph of all metaphase
chromosomes in a cell, arranged in
pairs by length and location of
centromeres
• Detects abnormal chromosomal
numbers and structural
abnormalities
Karyotyping
A Human Karyotype is a picture of all the matched pairs of human
chromosomes from one cell, …
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