CHROMOSOMES SF

Who first observed chromosomes and when

Walther Fleming in 1882

Where were chromosomes first observed

In tumor cells

Why were chromosomes first observed in tumor cells

Because in tumor the cells divide fast and the mass or tumor grows fast due to multiplying cells

What does actively dividing cells mean

We could see a lot of active nuclei

How many chromosomes do eukaryotes have

More than one

What is the shape of eukaryotic chromosomes

Linear rather than circular

Where are eukaryotic chromosomes located

Sequestered within a nucleus

What are eukaryotic chromosomes composed of

DNA and globular proteins (histones)

What are nucleosomes

10 nm diameter beads

What is chromatin

30 nm diameter, a very thin material

What are active genes in chromosomes called

Euchromatin

What is inactive DNA in chromosomes called

Heterochromatin

How many chromosomes do humans have

46 (44 autosomes; 2 sex chromosomes)

How many chromosomes does a fruit fly have

8 (2x)

How many chromosomes does a kingfisher have

132 (2x)

How many chromosomes does tobacco have

48 (4x)

How many chromosomes does an adder’s tongue fern have

1260 (2x)

Where is extranuclear DNA found in eukaryotes

Mitochondria, chloroplasts

What is the shape of extranuclear DNA

Circular

What does extranuclear DNA code for

5% RNA and polypeptides (nonfunctional) required for the organelle replication and function

Where are plasmids found

Fungi and protozoa

What plasmid is present in S. cerevisiae

70 copies of a plasmid (2μm circle)

What is a prokaryotic chromosome

A single molecule of DNA in the form of a closed loop

Give an example of a prokaryote with both linear and circular DNA

Agrobacterium tumefaciens = 1 linear, 1 circular

Give an example of a prokaryote with two circular chromosomes

Vibrio cholerae = 2 circular

What is the bacterial chromosome

Circular molecule of DNA associated with proteins and RNA

Where is the prokaryotic chromosome located

Nucleoid

How are prokaryotic chromosomes folded

Into loops that are 50,000 – 100,000 bp

What are plasmids

Small, circular molecules of DNA

What is the size range of plasmids

Few thousand bp to million bp

What information do plasmids carry

Required for replication, cellular traits

What are fertility (F) factors

Plasmids for conjugation and transfer of genes

What are resistance (R) factors

Plasmids that carry genes for resistance to one or more antimicrobial drugs, heavy metals, or toxins

What are bacteriocin factors

Plasmids that carry genes for proteinaceous toxins (bacteriocin)

What are virulence plasmids

Plasmids that make microorganisms pathogenic and cause disease when they enter the human body

What is a telomere

The ends of the chromosomes

What is a centromere

The primary constriction of the chromosomes; divides the chromosome into a short arm (p) and a long arm (q)

What is a chromatid

A single molecule of DNA

How are chromosomes classified

By size and position of centromere

What is a metacentric chromosome

A chromosome with the centromere in the middle

What is a submetacentric chromosome

A chromosome where the centromere divides it into 1/3 and 2/3

What is an acrocentric chromosome

A chromosome with the centromere near the end

What is the rule for placing the chromosome arms

P arm is always placed upwards, Q arm is always placed downwards

Who are cytogeneticists

Scientists who recognize and identify gross chromosomal abnormalities by examining chromosomes through a microscope

What three things do cytogeneticists use to tell chromosomes apart

Chromosome size, the position of the centromere, characteristic banding patterns of alternating light and dark bands (caused by staining with dyes)

What is a normal male karyotype

46, XY

What is a normal female karyotype

46, XX

What dye is often used in the “classic” karyotype

Giemsa (G-banding)

What dye is less frequently used in karyotyping

Quinacrine

What does Giemsa bind to

Phosphate groups of DNA

What does Quinacrine bind to

Adenine-thymine rich regions

What helps identify chromosomes

Each chromosome has a characteristic banding pattern; both chromosomes in a pair have the same banding pattern

How are karyotypes arranged

With the short arm on top and the long arm on the bottom

What is the short arm of the chromosome called

P arm

What is the long arm of the chromosome called

Q arm

How are stained regions and sub-regions numbered

From proximal to distal on the chromosome arms

What is spectral karyotyping

A molecular cytogenetic technique used to simultaneously visualize all pairs of chromosomes in different colors

How are fluorescently labeled probes made

By labeling chromosome-specific DNA with different fluorophores

Why is combinatorial labeling used

Because there are a limited number of spectrally-distinct fluorophores, it generates many different colors

What instrument captures spectral differences

An interferometer attached to a fluorescence microscope

What assigns pseudo colors to each chromosome

Image processing software

What is the disadvantage of using more colors

The more colors used, the more expensive it will be

What is digital karyotyping

A technique used to quantify DNA copy number on a genomic scale

How is digital karyotyping done

By isolating and enumerating short sequences of DNA from specific loci across the genome

What is another name for digital karyotyping

Virtual karyotyping