Transcript Chromosomes, genes, alleles, and mutation

Chromosomes,
genes, alleles, and
mutation
Topic 4.1
Assessment Statements
4.1.1 State that eukaryote
chromosomes are made of DNA
and proteins.
4.1.2 Define gene, allele and
genome.
4.1.3 Define gene mutation.
4.1.4 Explain the consequence of a
base substitution mutation in
relation to the processes of
transcription and translation, using
the example of sickle-cell anemia.
Organization of
chromosomes
• Chromosomes are
bundles of long strands
of DNA associate with
proteins
• Occur in pairs (except in
sex cells or gametes) in
sexually reproductive
eukaryotes
• Humans have 23 pairs
• Prokaryotes only have
one chromosome and
DNA is not associated
with proteins
Gene
• A heritable factor
that controls a
specific
characteristic or
genetic trait
• Passed on from
parent to
offspring
• Humans possess
an estimated
30,000 genes
Alleles
• A specific form of a
gene, such as eye
color or hair color
• Differ from other
alleles by only one
or a few bases
• Alleles of the same
gene occupy a
corresponding place
(locus) on each
chromosome of a
pair
Genome
• The complete set
of an organism’s
base sequences
• Used to find out
which gene does
what
ANG
Gene mutation
• A random, rare change in genetic
material
Base substitution mutation
• Changing of one base
could result in a different
amino acid placed in a
growing polypeptide
chain
• May have little or no
effect on the organism
• May have a major
influence
• Ex. Extra pair of wings,
change in eye color,
number of legs, etc.
Sickle cell anemia
• Base substitution found
in the gene which
creates hemoglobin for
red blood cells
• GAG becomes GTG
• During translation
instead of adding
glutamic acid, valine is
added instead
• Since valine has a
different shape and
properties, the shape of
the polypeptide chain is
changed
• Mutation gives a
different shape to the
hemoglobin molecule
• Difference leads to rbcs
having a curved shape
Symptoms of sickle cell
anemia
•
•
•
•
Weakness
Fatigue
Shortness of breath
Causes
– Oxygen cannot be carried as
efficiently
– Rbcs tend to crystalize causing them
to be less flexible
– Rbcs get stuck in capillaries
Critical thinking
What has ensured that the
frequency of the gene that causes
sickle cell anemia in a population
is balanced with the normal gene’s
frequency?