GENETICS
Exam I Review
Chapters 4
Define the word
homologous?
Refers to a pair of
chromosomes that are
substantially alike in size and
gene content, carrying the
same genes in the same
relative positions.
Define the word
Chromosome?
A linear end to end
arrangement of genes
and other DNA.
Define the word
chromomere?
A small beadlike structure
visible on a chromosome
during prophase of
meiosis and mitosis.
Define the word
Chromocenter?
The point at which the
polytene chromosomes
appears to be attached
together.
Define the word
Chromatin?
The substance of
chromosome; now know
to include DNA,
chromosomal proteins,
and chromosomal RNA.
Which of the following
have a mitochondrial
genome: a fish, a moss, a
palm three, baker’s yeast,
a bacterium?
All except bacterium
Which of the following
have a chloroplast
genome: a diatom, a
snake, a mushroom, E.
coli, mistletoe?
Diatom and Mistletoe
List the forces that hold
the DNA double helix
together as a stable unit.
Covalent and Hydrogen
Bonds
Where do covalent bonds
occur in the DNA doulble
helix?
Covalent bond bind the
sugars, phosphates, and
bases together.
Where do the Hydrogen
bonds occur in the DNA
double helix?
Hydrogen bonds occur
between the two strands
and hold a base with one
strand to the second
complimentary strand.
If thymine makes up 15
percent of the bases in a
certain DNA sample,
what percentage of bases
must be cytosine?
DNA is double stranded so
A+T+C+G = 100%
If A=15% then T=15%
so A-T=30%-100%=70%
70%/2(C-G)=35% each (C and G)
Somebody tells you the G
content of the DNA in a
certain species is 55%.
Why should you be
suspicious about this
statement?
Because 55% G does not
allow enough % for its
complimentary C, let
alone A-T.
If someone tells you that
a certain DNA sequence
is GTTAACGCT, what
information would you
need in order to assess its
orientation within the
DNA double helix?
Whether this information
is written 3’ to 5’ or 5’
to3’.
An organism has 5
chromosomes in its body
cells. Can you tell from
this if its likely to be
haploid or diploid?
Yes. Diploid organism usually
have two copies of each
chromosome. An odd
number of chromosomes
normally indicates a haploid
organism.
An organism has 6
chromosomes in its cells.
Can you tell from this if it
is haploid or diploid?
No. While an odd number usually
indicates a haploid organism, an
even number does not always
indicate a diploid organism. This
organism could be haploid with 6
different chromosomes or diploid
with 3 pairs of chromosomes.
How many hydrogen
bonds hold G+C and A+T
strands together in a 1-kb
(kilo-base) DNA molecule
if G+C content is 60%?
There are 1000 bases in a 1-kb DNA
molecule. 3 Hydrogen bonds hold
each G+C together and 2 Hydrogen
bonds hold together each A+T
together.
60% G+C is 600x3= 1800
40% A+T is 400x2= 800
1800+400= 2600 Hydrogen Bonds
If species A has more
DNA per nucleus than
species B does A
necessarily have more
genes than B? Why?
No. Different organisms have
varied size genes because of
the number of introns
(noncoding regions) and
amount of repetitive DNA.
If G+C content of a DNA
sample is 48%, what will
the proportions of the
four different
nucleotides?
100% - 48% (24%G+24%C)
= 52% (26%A+26%T)
Each cell of the human
body (excluding gonads)
contain 46 chromosomes.
What are the poidy level
and haploid number?
Human somatic cells are
diploid (2n) and the
haploid number is 23
(n=23).
How many DNA
molecules are there in
the nucleus of the human
cell?
46 DNA molecules
(chromosomes)
A certain segment of DNA
has the following
nucleotide sequence in one
strand:
5’ ATTGGCTCT 3’
What must be the sequence
in the other strand?
5’ ATTGGCTCT 3’
3’ TAACCGAGA 5’
The most common
elements in living
organisms are carbon,
hydrogen, oxygen,
phosphorus, and sulfur.
Which of these is not found
in DNA?
Sulfur
Why is the simplest
definition of a gene
incomplete?
A gene is a chromosomal region
capable of making a functional
transcript.
It does not take into account
inrons, exons, and regulatory
regions. It only describes a
gene as a chromosomal
region capable of making a
functional transcript.
The genome of bacterium Hemophilus
influenzae is 1830 kb in size, and
sequencing has shown it has 1703
genes.
What proportion is
expected to be introns?
0% Bacteria do not have
introns.
The gene for human protein albumin is
25kb long from, but the messenger
RNA for this protein is only 2.1kb long.
What do you think accounts
for this huge difference?
Introns. In this case, the
25kb primary transcript
has all but 2.1kb removed
to generate the proper
mRNA for translation.
The genome of bacterium Hemophilus
influenzae is 1830 kb in size, and
sequencing has shown it has 1703
genes.
What proportion is
expected to be introns?
0% Bacteria do not have
introns.
If the DNA from cells of Neurospora, a
haploid fungus (n=7) is separated using
pulsed field gel electrophoresis (PFGE),
how many bands will be
produced?
7 bands should be
produced using PFGE.
If the DNA from cells of pea, a diploid
plant (2n=14) is separated using
pulsed field gel electrophoresis (PFGE),
how many bands will be
produced?
7 bands should be
produced using PFGE.
Why are only 7 bands
produced in the diploid
plant (2n=14)?
Homologous
chromosomes will comigrate as a single band.
Devise a formula that
relates size of mRNA to
gene size, number of
introns, average size of
introns, and size of the
regulatory region.
gene size – (number of introns x average size of introns) - size of regulatory region
= mRNA size
DRAW the following pieces
of DNA in the style of Figure
2-5b:
5’ ATGCT 3’
3’ TACGA 5’
3’ ATGCT 5’
5’ TACGA 3’