Gene and Chromosomal Mutations Topic 4.1 and 4.2

Gene and Chromosomal Mutations

Topic 4.1 and 4.2

A Eukaryotic Chromosome is made up of DNA

and Protein

http://www.biochem.arizona.edu/classes/bioc462/462a/NOTES/Nucleic_Acids/chromosome2.jpg

Gene:

• A gene is the stretch of DNA that codes for One protein. A gene is a heritable factor that controls a specific characteristic. There are several types of Genes:– Genes that make proteins– Structural genes,– Regulator genes, – genes that code for tRNA and rRNA.

As a Human you have 46 Chromosomes in 23 pairs.

• One of each pair came from one parent and the other came from the other.

• Each pair carries the same sets of genes in the same positions.

• They are homologous.

This is a picture of a flower chromosome!

http://www.bio.miami.edu/~cmallery/150/mendel/allele.jpg

Allele• An allele is one specific form of a gene, differing

from other alleles by one or a few bases only and occupying the same gene locus (position) on a chromosome as other alleles of the gene.

• Because you have 2 of each chromosome you can potentially have 2 alleles (versions) of each gene.

• E.g. Gene = Eye colour

Allele = Brown eyes.

• Remember?

Alanine

G C U

DNA RNA Protein

• And Codons and Anti-Codons

Methionine

A U G

Glycine

G G G

stop

U G A

U A C C G A C C C A C U

http://scienceblogs.com/oscillator/genetic%20code.jpg

Proline

C C U

Methionine

A U G

Glycine

G G G

stop

U G A

U A C G G A C C C A C U

What will happen if I change a Nitrogen base on the DNA?

Alanine

G C U

Methionine

A U G

Glycine

G G G

stop

U G A

U A C C G A C C C A C U

Would become:

…..a slightly different protein, OR a variant of the gene – Also called an Allele.

Eg. Brown Protein made

Eg. Green Protein made

• Sometimes the changes are when one base is replaced with another – A Substitution mutation

• Sometimes one base is added – An Addition mutation

• Sometimes a base is lost – A Deletion mutation.

• This is how new alleles come about.

Predict what you think would happen to thesequence below if the G were removed frommRNA.

Proline

C C U

Methionine

A U G

Glycine

G G G

stop

U G A

U A C G G A C C C A C U

Would become:

What would happen to the sequence if another base were added instead of the G being removed?

Sickle-cell Anemia

http://media-2.web.britannica.com/eb-media/20/76520-004-27CD47E9.jpg

http://services.epnet.com/GetImage.aspx/getImage.aspx?ImageIID=2560

This misshaping of the blood cells is due to GAG being mutated to GTG causing Glutamic acid to be replaced by valine!

This causes a reduction in oxygen-carrying capacity of the blood; pale skin, fatigue and difficulty breathing.

What would happen to the protein produced if an early codon got changed to a “STOP” codon?

If a person has 2 copies of almost all alleles, one of which has this early “stop” codon, (because they possess 2 copies of every chromosome) Will the protein that this allele is coding for still get made?

Does this explain dominant and recessive genes?

Think…….

Genome

• The genome is the whole of the genetic information of an organism.

• Look up the Human Genome Project. What can it tell us? How was it done? Who is J.Craig Ventor?

Karyotyping

• We can look at our chromosomes during Mitosis. If we add stain the proteins in the chromosomes take it up differently. We take a picture of them. We can then pair up homologues according to size and banding.

• This is used to look for chromosomal abnormalities in a fetus, (and to determine the gender of a person – Olympics committee!)

http://www.mhhe.com/socscience/sex/common/ibank/ibank/0111.jpg

• Shows 23 pairs of chromosomes. Twenty two pairs are called autosomes, 1 pair is called the sex chromosomes ; XY in a male.

http://www.kscience.co.uk/as/module2/dna_structure/DNA_files/History%20of%20DNA%20research.htm

A Male

• Shows 23 pairs as in the male, but sex chromosomes are represented by XX.


A Female

• Sometimes there are errors made during Meiosis. This leads to a Chromosome Mutation. It is called Non-Disjunction. (More explanation when we do Mitosis.)

Eg.

Down’s Syndrome

Turners Syndrome

Klienfelter’s syndrome

• Associated with 3 copies of chromosome number 21(trisomy of chromosome 21), rather than the 2 found normally. Down syndrome is characterized by differing degrees of mental retardation, a skin fold over the eye, typically short stature, and short hands with a deep crease in the palm. Down is also known as mongolism (mongoloid).


• Three sex chromosomes are associated with Klinefelter rather than the expected 2 - XXY. These individuals are males with some development of breast tissue normally seen in females. Little body hair is present, and such person are typically tall, with or without evidence of mental retardation.


• Only 1 sex chromosome is present - X0. The expected Y chromosome is missing. Turner syndrome is associated with underdeveloped ovaries, short stature, webbed/.bull neck, and broad chest. Individuals are sterile, and lack expected secondary sexual characteristics. Mental retardation typically not evident.

http://femalecare.net/wp-content/uploads/2009/03/turner-syndrome.jpg

Documents

Gene and Chromosomal Mutations Topic 4.1 and 4.2