Mutations

What Are Mutations? Changes in the nucleotide sequence of DNA May occur in somatic cells (aren’t passed to offspring) May occur in gametes (eggs & sperm) and be passed to offspring

Are Mutations Helpful or Harmful? Mutations happen regularly Chemicals & UV radiation cause mutations Many mutations are repaired by enzymes

Are Mutations Helpful or Harmful? Some type of skin cancers and leukemia result from somatic mutations Some mutations may improve an organism’s survival (beneficial)

Types of Mutations

Chromosome Mutations May Involve: Changing the structure of a chromosome The loss or gain of part of a chromosome

Chromosome Mutations Five types exist: Deletion Inversion breakage of chromosomes Deletion Inversion Translocation Duplication Incorrect number of chromosomes Nondisjunction chromosomes don’t separate properly during meiosis

Alterations of Chromosome Structure A deletion occurs when a chromosome fragment lacking a centromere is lost during cell division. This chromosome will be missing certain genes. A duplication occurs when a fragment becomes attached as an extra segment to a sister chromatid. Images from: Biology; Campbell and Reese; Pearson Education, Inc., publishing as Benjamin Cummings Slide from: Slide show by Dr. Chuck Downing

Alterations of Chromosome Structure Chromosomal translocations between nonhomologous chromosome are also associated with human disorders. Chromosomal translocations have been implicated in certain cancers, including chronic myelogenous leukemia (CML). CML occurs when a fragment of chromosome 22 switches places with a small fragment from the tip of chromosome 9. Normal chromosome 9 Reciprocal translocation Translocated chromosome 9 Philadelphia chromosome Normal chromosome 22 Translocated chromosome 22 http://www.antigenics.com/diseases/images/philly_chrom.gif

Alterations of Chromosome Structure An inversion occurs when a chromosomal fragment reattaches to the original chromosome but in the reverse orientation. In translocation, a chromosomal fragment joins a nonhomologous chromosome. See a Video See a Video Slide from: Slide show by Dr. Chuck Downing Images from: Biology; Campbell and Reese; Pearson Education, Inc., publishing as Benjamin Cummings

Duplications and translocations are typically harmful Cri du chat Is a disorder caused by a deletion in chromosome #5 Mental retardation Small head Unusual facial features “cat cry” http://www.morfosa.org/medweb/patologi/bilder/cri-du-chat.gif

PRADER-WILLI Syndrome Victor Age 1 / Victor Age 2 Born floppy and pale At first refuse to nurse, but later eat until they become obese Tiny hands and feet Underdeveloped sex organs Mildly retarded Spectacular temper tantrums especially if refused food Exceptional proficiency with Jig-saw puzzles Missing piece of chromosome #15

ANGELMAN’S SYNDROME Taut, not floppy Thin Hyperactive Insomniac Small head Move jerkily like puppets Happy disposition Severely mentally retarded Rarer than Prader-Willi Missing SAME piece of Chromosome #15 Colin Farrell’s son has Angelman’s syndrome http://www.usmagazine.com/colin_farrell_and_son

Nondisjunction – Failure of homologous chromosomes OR chromatids to separate at anaphase Nondisjunction Normal Meiosis

Nondisjunction Results in ANEUPLOIDY = one or more chromosomes have extra or missing copies AFTER FERTILIZATION: Cell with only 1 copy of a chromosome instead of 2 = MONOSOMY Cell with 3 copies of a chromosome instead of 2 = TRISOMY

Polyploidy -common among plants Enduring understanding 3.C: The processing of genetic information is imperfect and is a source of genetic variation. Essential knowledge 3.C.1: Changes in genotype can result in changes in phenotype. c. Errors in mitosis or meiosis can result in changes in phenotype. Evidence of student learning is a demonstrated understanding of each of the following: 1. Changes in chromosome number often result in new phenotypes, including sterility caused by triploidy and increased vigor of other polyploids. [See also 3.A.2] Polyploidy -common among plants Ex: Strawberries = octaploid wheat = hexaploid Much less common in animals LETHAL in humans Polyploids are more nearly normal in phenotype than aneuploids. http://tasty-dishes.com/data_images/encyclopedia/strawberry/strawberry-03.jpg Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

POLYPLOIDY Organisms with more than two complete sets of chromosomes Can occur when a normal gamete fertilizes another gamete in which there has been nondisjunction of all its chromosomes. Results in triploid (3n) zygote OR if 2n zygote fails to divide after replicating its chromosomes Results in a tetraploid (4n) embryo Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

Down syndrome (Trisomy 21) Most common chromosomal abnormality (1 in 800 births) Similar facial features Slanted eyes / Protruding tongue Mild to severe mental retardation 50% have heart defects that need surgery to repair Both older (35+ years) and younger (under 16 years) mothers are more at risk. http://www.healthofchildren.com/images/gech_0001_0002_0_img0096.jpg

Sex chromosomes abnormalities Human development more tolerant of wrong numbers in sex chromosome But produces a variety of distinct syndromes in humans XXY = Klinefelter’s syndrome male XXX = Trisomy X female XYY = Jacob’s syndrome male XO = Turner syndrome female

Turner syndrome (X0) 1 in 5000 births http://medgen.genetics.utah.edu/photographs/diseases/high/611.gif Turner syndrome (X0) 1 in 5000 births Females have only one X chromosome Small size Broad chest Slightly decreased intelligence 35% have heart abnormalities Hearing loss common Reproductive organs don’t develop at puberty

Klinefelter syndrome 1 in 2000 births live births http://www.akdeniz.edu.tr/tip/histoloji/embrders_dosyalar/slide0228_image1186.jpg Klinefelter syndrome 1 in 2000 births live births Males have extra X chromosomes (Can be XXy, XXXy, or XXXXy) Taller than average Normal intelligence have male sex organs, but are sterile. may be feminine characteristics, Often not discovered until puberty when don’t mature like peers Presence of BARR BODIES

Image from Biology; Campbell and Reece; Pearson Prentice Hall publishing as Benjamin Cummings © 2006

Karyotype can show: Sex of baby Missing or extra chromosomes Major deletions or translocations Can’t see individual gene changes http://content.answers.com/main/content/wp/en/thumb/f/f3/220px-Down_syndrome_translocation.png

Gene Mutations Change in the nucleotide sequence of a gene May only involve a single nucleotide May be due to copying errors, chemicals, viruses, etc.

Types of Gene Mutations Include: Point Mutations Substitutions Insertions Deletions Frameshift

Point Mutation Change of a single nucleotide Includes the deletion, insertion, or substitution of ONE nucleotide in a gene

Point Mutation Sickle Cell disease is the result of one nucleotide substitution Occurs in the hemoglobin gene

Frameshift Mutation Inserting or deleting one or more nucleotides Changes the “reading frame” like changing a sentence Proteins built incorrectly

Frameshift Mutation Original: The fat cat ate the wee rat. Frame Shift (“t” deleted): The fat caa tet hew eer at.

Amino Acid Sequence Changed