Download Chromosomes, Alleles, Genes, Mutations

4.1 Genetics: Chromosomes,
Alleles, Genes, Mutations
Genetics (the study of inheritance): The
scientific discipline involved with
studying how genes/traits are passed
from parent to offspring.
IB ASSESSMENT STANDARDS
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 consequences of a base
substitution mutation in relation to the
processes of transcription and translation,
using the example of sickle cell anemia.
Genes and Alleles

Gene: a heritable factor
that controls a specific
characteristic



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Located in specific
places on chromosomes
Humans have roughly
20,000-25,000 genes.
Alleles: alternative
forms of gene
Example:


Gene: eye color
Alleles: blue vs. brown
Genes
Chromosomes


Prokaryotes ‘Naked DNA’
Eukaryotic chromosomes


Made of DNA and proteins
Two Types:

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
Two parts

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Autosomes (non sex
chromosomes)
Sex Chromosomes
Sister Chromatids
Centromere
Homologous
Chromosomes:
chromosomes that have the
same genes as each other,
arranged in the same sequence,
but not necessarily the same
alleles of those genes
Chromosome & Gene Numbers of
Different Organisms
Karyotyping


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A karyotype is a
display (micrograph)
of the number and
type of chromosomes
a nucleus contains.
Cells are examined in
metaphase of mitosis.
The stained
chromosomes are
arranged according to
size and structure.
How are Karyotypes Useful?

One of the main
reasons for
karyotyping is to find
out whether a fetus
has Down
Syndrome or other
chromosomal
abnormalities.

Karyotyping can be
done by extracting
and examining fetal
cells
(amniocentesis) or
through chorionic
villus sampling
(examining cells
from the placenta).
Detecting Fetal Abnormalities
Amniocentesis
Chorionic Villus Sampling
Mutations

Mutations are changes in the sequence of bases
in a gene.
 Changes in the sequence of bases cause
changes to the amino acid sequences which
change structure and function of the resulting
protein.
 DNA Mutations vs. Chromosomal/Gene
Mutations
DNA Mutations

Point Mutations

Caused by base pair
substitutions



The replacement of one
nucleotide and its partner with
another pair
Changes the amino acid the
codon codes for and the protein
Types:



No effect: the amino acid
sequence is not effected;
protein not changed
Missense: the codon codes for
a different amino acid; protein
changed
Nonsense: the codon codes
for STOP; protein changed
DNA Mutations

Frameshift Mutations



Caused by inserting or
deleting a nucleotide pair
Changes the amino acid
sequence from the point of
the mutation to the end of
the polypeptide chain
Types:


Nonsense: new base
added creating a STOP;
protein changed
Missense: removal of a
base creating new codons;
protein changed
Gene Mutations (Chromosomal)

Deletion


Duplication

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Reverses a segment within a
chromosome
Translocation


Repeats a segment
Inversion


Removes a chromosomal
segment
Moves a segment from one
chromosome to another
nonhomologous one
Alteration of Chromosome
number

Nondisjunction (we will discuss
this more during Meiosis)
Sickle-Cell Anemia (KNOW THIS)

Normal hemoglobin has 4
subunits, 2 a chains and 2 b
chains. A single base pair
substitution can change the
shape of the b chains, causing a
sickle shape in red blood cells.

Correct Base Pair Sequence:
 CTT (DNA)
 GAA (mRNA)
 Glu (amino acid)
 End result: normal hemoglobin,
normal shaped cells
Mutation Base Pair Sequence:
 CAT (DNA)
 GUA (mRNA)
 Val (amino acid)
 End result: abnormal hemoglobin
and sickle shaped cells

Sickle Cell Anemia
(An Introduction)
Hemoglobin



Hemoglobin is found
in red blood cells.
The function of this
protein is to carry
oxygen throughout
the bloodstream.
All cells require
oxygen for cellular
respiration.


Normal Hemoglobin
Abnormal Hemoglobin
Sickle-Cell Anemia
Signs & Symptoms:

Anemia
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Shortness of breath,
dizziness, headaches,
coldness in hands/feet, pale
skin, jaundice.
Pain Throughout the Body
Blocked Blood Flow
Infections
Pulmonary Hypertension
Stroke
Multiple Organ Failure
Mutation Practice (Sickle Cell Anemia)

Sickle Cell/Protein Synthesis Handout
The Most Unusual Mutations
‘Genome’


Genome: the whole of the genetic information
of an organism
The Human Genome Project
Completed in 2003

The mapping of human chromosomes/genes.
The Human Genome Project