Genome
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closely related species have almost identical genes but may have:
very different chromosome numbers
if closely related species with different chromosome numbers interbreed:
*embryonic mitotic divisions may generate a viable adult, but: *the hybrid will be sterile due to meiotic failure
during interphase, most of the DNA (90%) is
decondensed: euchromatin (true chromatin).
Some DNA (~10%) remains condensed, as in metaphase:
heterochromatin, which is dark-staining.
The nucleolus is the region of the nucleus where the:
transcription of rRNA genes and the assembly of ribosomes occur.
the nucleolus contains:
many copies of rDNA (rRNA genes, generated by gene amplification), and ribosomal proteins. It is dark-staining due to its high transcriptional activity.
Heterochromatin is DNA that remains:
condensed and is transcriptionally inactive during the entire cell division cycle, including interphase.
heterochromatin is an example of an
epigenetic transformation of DNA.
Constitutive heterochromatin:
are the regions of the chromosomes that are invariably heterochromatic in all cells in an organism.
Facultative heterochromatin:
are the regions of the chromosomes that contain genes but can become heterochromatic depending on the cell type.
The position of a gene relative to heterochromatin:
may affect its expression.
the White gene in Drosophila is necessary for the:
normal (wild-type) red eye pigmentation. *the absence of its product results in white eyes
if the White gene is moved close to heterochromatin DNA and the barrier is relocated by a rare chromosomal inversion:
some of the eye cells may not express the gene
A transposition in patients with inherited ataxia causes:
a piece of chromosome 4 to become inappropriately attached to chromosome 12.
A transposition in patients with inherited ataxia affects:
This affects the normal expression of genes near the breakage point
inherited ataxia is characterized
by the progressive deterioration of motor skills.
LINEs and SINEs:
long and short interspersed nuclear elements.
Tandemly repeated DNA:
satellites
Repetitive DNA sequences are:
non-coding sequences that are present in multiple copies
interspersed repeats are:
repeated sequences that are not clustered but are scattered throughout the genome
simple sequence DNA:
(“satellites”) are tandemly (end to end) clustered repeats
Examining repetitive sequences: Reassociation assay : step 1
Cut the DNA with restriction enzymes.
Examining repetitive sequences: Reassociation assay : step 2
Denature the DNA fragments by heating
Examining repetitive sequences: Reassociation assay : step 3
Allow the DNA to cool down slowly and reassociate.