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? RNA DNA Protein And Codons and Anti-Codons

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

What will happen if I change a Nitrogen base on the DNA? Eg. Brown Protein made Would become: Eg. Green Protein made …..a slightly different protein, OR a variant of the gene – Also called an Allele.

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 the sequence below if the G were removed from mRNA. Would become: What would happen to the sequence if another base were added instead of the G being removed?

Sickle-cell Anemia 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. http://services.epnet.com/GetImage.aspx/getImage.aspx?ImageIID=2560 http://media-2.web.britannica.com/eb-media/20/76520-004-27CD47E9.jpg

Think……. 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?

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

A Male 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 Female Shows 23 pairs as in the male, but sex chromosomes are represented by XX. http://www.kscience.co.uk/as/module2/dna_structure/DNA_files/History%20of%20DNA%20research.htm

Sometimes there are errors made during Meiosis 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). http://www.kscience.co.uk/as/module2/dna_structure/DNA_files/History%20of%20DNA%20research.htm

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

Only 1 sex chromosome is present - X0 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