Chromosomes (3.2) Flashcards

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1
Q

Prokaryote genetic material

A

A single chromosome consisting of a circular DNA molecule (genophore). May possess additional genetic material in plasmids. DNA is naked - not associated with proteins.

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2
Q

Eukaryote genetic material

A

Homologous chromosomes. One of maternal origin and one of paternal origin. DNA is packaged with histone proteins.

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3
Q

Describe the packaging of DNA in eukaryotic cells.

A

DNA is wound around eight histone proteins to form a nucleosome. Nucleosomes are linked by an additional histone protein to form a string of chromatosomes. These then coil to form a solenoid structure which is condensed to form a 30 nm fibre. These fibres then form loops, which are compressed and folded around a protein scaffold to form chromatin. Chromatin will then supercoil during cell division to form chromosomes that are visible (when stained) under a microscope.

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4
Q

Define diploid.

A

Nuclei possessing pairs of homologous chromosomes (2n). Two alleles for each trait. Sexually reproducing organisms are diploid.

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5
Q

Define haploid.

A

Nuclei possessing only one set of chromosomes (n). Single allele for each trait.

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6
Q

What are the sex chromosomes in humans?

A

Females (XX)Males (XY)

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7
Q

What is a karyogram?

A

A diagram or photograph of the chromosomes in a cell, arranged in homologous pairs and in a numbered sequence. A visual profile.

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8
Q

What is a karyotype?

A

An individual’s complete set of chromosomes.

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9
Q

Process of a karyotype.

A
  • A sample of cells is harvested. Usually from a foetus or white blood cells of adults.- The cells are chemically induced to undergo mitosis and stop at metaphase.- The chromosomes are stained and spread out on a slide, then photographed.- The photograph is cut up and the chromosomes are arranged in homologous pairs according to size, shape, banding patterns and the position of the centromere.
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10
Q

What is karyotyping used for?

A

Pre-natal diagnosis of chromosomal abnormalities eg. downs syndrome. It’s also used to determine the gender of the baby (via identification of the sex chromosomes).

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11
Q

What is Downs Syndrome?

A

A condition due to a mutation where the individual has an additional copy of chromosome 21, i.e. three rather than two.

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12
Q

Cairns’ technique

A

Used to measure the length of DNA molecules by autoradiography. John Cairns incubated bacterial cells in a solution containing radioactive thymidine. The solution was incorporated into the chromosomal DNA of the cell. The chromosomes were isolated from the cell and fixed to a photographic surface where they were immersed in silver bromide. When the photographic film developed the chromosomal DNA was able to be visualised with an electron microscope.

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