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Blueprint Series

Complete Solution
Chapter 8

8
GENES, GENOMICS,
AND CHROMOSOMES

REVIEW THE CONCEPTS
1
...
This definition
includes introns and the regulatory regions (e
...
, promoters and enhancers of the
gene)
...
Single or solitary genes are present once in the haploid genome
...
Gene families are sets of duplicated genes that encode proteins with similar but nonidentical
amino acid sequences
...
Pseudogenes are copies of genes that are nonfunctional even though they seem to have the
same exon-intron structure as a functional gene
...
Tandemly repeated genes are present in a head-to-tail array of exact or
almost exact copies of genes
...

3
...
Microsatellites
contain repeats that contain 1–13 base pairs
...
The number of copies of the tandemly repeated DNA
sequences varies widely between individuals
...
This technique can distinguish and identify individuals on the basis
of differences in the number of repeats in their micro- and minisatellite simplesequence DNA
...
A bacterial insertion sequence, or IS element, is a member of the class of mobile
DNA elements
...
Between the inverted repeats is a region that encodes the
enzyme transposase
...
First,
transposase excises the IS element in the donor DNA; second, it makes staggered
cuts in a short sequence in the target DNA; and, third, it ligates the 3’ termini of
the IS element to the 5’ ends of the cut donor DNA
...

5
...
One class of retrotransposons, the LTR retrotransposons, contain long terminal repeats (LTRs) at
their ends and a central protein coding region that encodes the enzymes reverse
transcriptase and integrase
...
This RNA intermediate is then converted into DNA by
the action of reverse transcriptase primed with a cellular tRNA in the cytoplasm
...
Retrotransposons that lack LTRs transpose
by a different mechanism
...
The LINE element is first transcribed by host RNA polymerase and
exported to the cytoplasm, resulting in the translation of ORF1 and ORF2
...
The resulting T-rich strand of chromosomal DNA then hybridizes to the poly (A) tail at the 3’-end of the LINE RNA
and primes reverse transcription of the RNA by ORF2 protein
...

6
...
In addition, unequal crossing over between homologous mobile elements at different chromosomal locations leads to exon duplications, gene duplications, and chromosomal rearrangements that can generate new combinations
of exons
...
The inclusion of flanking DNA during transposition also results in the movement of genomic DNA to another region of the

CHAPTER 8: Genes, Genomics, and Chromosomes

genome
...

7
...
e
...
Orthologous genes are genes that arose because of speciation (i
...
, genes found in different species that have very similar nucleotide
sequences and functions)
...
Thus, a small increase in gene number could result
in a very large increase in protein number
...
Also, complexity among multicellular organisms arises largely from
organizing a larger number of cells into more complex groups of interacting
cells
...

8
...
The protein core consists of an octamer, containing two copies of
histones H2A, H2B, H3, and H4
...
The
histone H1 binds to the linker region, which varies in length from 10 to 90
base pairs and is located between nucleosomes
...

9
...

As transcription factors and RNA polymerase must be able to access the DNA,
transcription will only occur when the DNA is loosely compacted
...
When a
gene is not actively transcribed, the chromatin would likely be methylated or
deacetylated
...
FISH, or fluorescent in situ hybridization, is one of many related techniques used
to detect DNA (or RNA) sequences in cells or tissues
...
Upon addition to the chromosomes, the
probe will bind to the DNA and be visible under a fluorescent microscope
...

The signal is detected using fluorescence microscopy
...
For example, patients with chronic
myelogenous leukemia possess leukemic cells with the Philadelphia chromosome, a shortened chromosome 22 containing genetic material translocated from
chromosome 9
...
By labeling leukemic cells with chromosome 9–specific
and chromosome 22–specific probes, each labeled with a different fluorescent
marker, one is able to identify and compare the size of the normal chromosomes
to those having undergone a translocation
...
Metaphase chromosomes can be identified by size, shape, banding
patterns, or hybridization to fluorescent probes (chromosome painting)
...
In this method, DNA probes labeled with
specific fluorescent tags are hybridized to metaphase chromosomes
...
Each chromosome then fluoresces with a
different combination of fluorescent tags
...
This way each chromosome can be
identified by its false-color image and size
...
Polytene chromosomes are present in larval salivary glands of the fruit
fly Drosophila melanogaster, and are also present in cells in other dipteran
insects andin plants
...
Polytene chromo- somes consist of multiple
gene copies, which when transcribed provide the cells with an
abundance of mRNA encoding proteins required for larval growth and
development
...
Replication origins are the points at which DNA synthesis is initiated
...
The
telomeres arespecialized structures located at the ends of linear
chromosomes
...
(b) The chro-mosome could be replicated,
but it may not be segregated evenly to the two daughter cells
...

14
...
Eventually, the RNA region is degraded
and DNA polymerase fills in the missing nucleotides
...
At the very ends of the chromosome, there is no
upstream Okazaki fragment, and thus it is not possibleto replace the
RNA nucleotides with DNA
...

While telomeres do not halt this problem, they ensure that the lost DNA
is non-coding DNA
...




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