Mutations and Karyotyping

Mutations Ch. 10. pg. 219-220 Changes in nucleotide sequence of DNA May occur in somatic cells (body cells) not passed to offspring May occur in gametes (eggs & sperm) passed to offspring

Causes Mutations happen regularly Any agent that causes a change in DNA is called a mutagen. Mutagens include radiation, chemicals, and even high temperatures. Ex. of radiation: X rays, cosmic rays, ultraviolet light, and nuclear radiation. Chemicals: Benzene Many mutations are repaired by enzymes.

Are Mutations Helpful or Harmful? Some harmful - Skin cancers and some leukemias result from somatic mutations Most mutations have no affect, some have detrimental affects and a few mutations may improve an organism’s survival (beneficial)

Types of Mutations 2-Types 1. Gene mutations - change in one DNA sequence of a gene. 2.Chromosomal mutations – change in structure or loss or gain of part of a chromosome.

Gene mutation- 2 types 1. Point Mutation A change in a single base pair in DNA. Changes the amino acid in the protein Does not always cause a problem. THE DOG BIT THE CAT THE DOG BIT THE CAR

2. Frameshift Mutation A single base is added or deleted from the DNA causing all the other bases to be out of position. More harmful than a regular point mutation. THE DOG BIT THE CAT THE DOB ITT HEC AT

Chromosome Mutations Five types exist: Deletion Inversion Translocation Nondisjunction Duplication

Deletion Part of a chromosome is lost/deleted. A B C D E F G H A B C E F G H

Duplication/Insertion A part of the chromosome repeats A B C D E F G H A B C B C D E F G H

Inversion Part of a chromosome breaks off; reattaches backward A B C D E F G H H A D C B E F G

Translocation Part of a chromosome breaks off; attaches to a different chromosome that is not homologous A B C D E F G H W X A B C D E F G H W X Y Z Y Z W X Y Z Y Z Translocation Translocation

Nondisjunction Failure of pair of chromosomes to separate during meiosis Example Down Syndrome

Chromosome Mutation Animation

Karyotyping Ch. 6 pg. 122-123

Some mutations that cause chromosomal abnormalities can be detected by analyzing a karyotype. Karyotype – photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size, number, and shape. Identifies gender and genetic disorders

2 types of abnormalities in chromosomes Amniocentesis – medical procedure used in prenatal diagnosis of chromosomal abnormalities and fetal infections small amount of amniotic fluid, which has fetal tissues, is extracted from the amniotic sac surrounding a developing fetus 2 types of abnormalities in chromosomes Autosomal abnormalities – abnormalities of chromosomes not directly involved in determining gender Sex Chromosomal abnormalities – abnormalities that affect the gender of an individual XX – female XY - male

How Scientists Read Chromosomes? To "read" a set of human chromosomes, scientists first use three key features to identify their similarities and differences: Size. This is the easiest way to tell two different chromosomes apart. Banding pattern. The size and location of Giemsa bands on chromosomes make each chromosome pair unique. Centromere position. Centromeres are regions in chromosomes that appear as a constriction. They have a special role in the separation of chromosomes into daughter cells during mitosis cell division (mitosis and meiosis). Image taken from: http://learn.genetics.utah.edu/content/begin/traits/scientists/ Using these key features, scientists match up the 23 pairs – one set from the mother and one set from the father.

Typical Karyotype

Typical Karyotype

Trisomy 21- Down’s Syndrome - Karyotype 47 Total Chromosomes Three Chromosomes at the 21st Pair Image taken from: http://worms.zoology.wisc.edu/zooweb/Phelps/karyotype.html

Monosomy X - Turner Syndrome - Karyotype 45 Total Chromosomes One “X” Chromosome Image taken from: http://worms.zoology.wisc.edu/zooweb/Phelps/karyotype.html

XYY Karyotype 47 Total Chromosomes One “X” and Two “Y” Chromosomes Image taken from: http://worms.zoology.wisc.edu/zooweb/Phelps/karyotype.html

Examples Cri du chat – deletion of #5 Wilson’s Disease – can’t get rid of excess copper Down's syndrome – extra copy of #21 Patau Syndrome – extra copy of #13 Klinefelter's syndrome (XXY) Turner syndrome (X instead of XX or XY) XYY syndrome. XYY Triple-X syndrome (XXX) XXXX Syndrome

Colored Blindness Hemophilia – bleeding disorder Huntington’s Disease – faulty protein (mental/nervous disorder) Jackson-Weiss Syndrome – fusion of face/foot bones Sickle Cell Disease – red blood cells sickle shaped Tay-Sachs Disease – brain/nerve disorder Polydactyly – extra digit