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12-4 Mutations 1 Mutation Gene = change in genetic material mutation = changes in a single gene Chromosomal mutation = changes in whole chromosomes (affects many genes) 2 Gene Mutations Point Mutations = Changes in one or a few nucleotides Include: substitutions, insertions, and deletions 3 Types of Point Mutations Substitutions = one base is changed to another Usually affects a single amino acid Insertions = one base is inserted Deletions = one base is deleted More dramatic changes Cause frameshift mutations • Changes all amino acids after the point of change 4 Frameshift Mutations mutation that shifts the “reading” frame of the genetic message by inserting or deleting a nucleotide May change every amino acid after that point Frameshift mutations can alter a protein so much that it is unable to perform its normal functions. 5 6 Chromosomal Mutations Changes in the number or structure of chromosomes May even change the number of copies of some genes 7 5 Types of Chromosomal Mutations Insertions = addition of part of a chromosome Deletions = loss of all or part of a chromosome Duplications = extra copies of parts of a chromosomes Inversions = reverse direction of parts of a chromosomes Translocations = part of one chromosome breaks off and attaches to another 8 Chromosomal Mutations 9 10 Significance of Mutations Most have little effect Most mutations occur in portions of the DNA that is not currently being used. Dramatic changes = usually harmful Producing defective proteins that don’t do their job Mutations = source of genetic variability! Can be very good! Useful! 11 Polydactyly 12-5 Gene Regulation A typical gene includes start and stop signals, with the nucleotides to be translated in between. Regulatory Sites = determine if gene is on or off. 14 Lac Repressor in E. coli Prokaryotic cells Cells turn genes on and off as needed 15 Eukaryotic Gene Regulation Similar but more complex than prokaryotes Many eukaryotic genes include a sequence called the TATA box that may help position RNA polymerase. 16 Enhancer sequences in DNA: Protein binding area that can enhance transcription by opening up tightly packed chromatin attract RNA polymerase block access to genes More complex because of cell specialization Not all proteins are needed in every cell 17 Chromosomal Mutations & their effects Karyotype A picture of the chromosomes of an individual (or a species), including number, form, and size of the chromosomes. Often used to diagnosis chromosomal abnormalities. Chromosomes Humans have 23 pairs 22 pairs are autosomes 1 pair are sex chromosomes • (women = XX, men = XY) Chromosomes have a centromere that holds the chromatids (two parts of the chromosome) together. The top ½ of the chromosome is called the “p” arm and the bottom ½ is “q” Nondisjunction Disorder Nondisjunction is the failure of chromosome pairs to separate during meiosis (making of gametes – sex cells) it can cause some gametes to gain an extra chromosome and others to lose one Monosomy = A chromosome having no homologue (matching chromosome) Trisomy =The condition of having three copies of a given chromosome in each somatic (body) cell rather than the normal number of two. Normal Male Karyotype Normal Female Karyotype Turners Syndrome 1 in 5,000 births 45 chromosomes X only #23 Monosomy Nondisjunction Turners Syndrome 96-98% do not survive to birth No menstruation No breast development No hips Broad shoulders and neck Cri-Du-Chat Syndrome 1 in 216,000 births 46 chromosomes XY or XX #5 Deletion of upper arm of chromosome Cri-Du-Chat Syndrome Moon-shaped face Heart disease Mentally retarded Malformed larynx Normal lifespan Aniridia-Wilms Tumor Syndrome 1 in 50,000,000 births 46 chromosomes XY or XX #11 Deletion of upper arm Aniridia-Wilms Tumor Syndrome Mentally retarded Growth retarded Blindness Tumors on kidneys Short lifespan Thirteen Q Deletion Syndrome 1 in 500,000 births 46 chromosomes XY or XX #13 Deletion of lower arm Thirteen Q Deletion Syndrome Mentally retarded No thumbs Short lifespan Deformed face Heart disease Prader-Willi Syndrome 1 in 5,000,000 births* (new info = 1 in 25,000) 46 chromosomes XY= 97% XX= 3% #15 Deletion of lower arm paternal chromosome (Angelman’s syndrome = 15 q deletion of maternal chromosome) Prader-Willi Syndrome Small bird-like head Mentally retarded Respiratory problems Obesity Short lifespan very flexible low muscle tone Eighteen Q Deletion Syndrome 1 in 10,000,000 births 46 chromosomes XY or XX #18 Deletion of lower arm Eighteen Q Deletion Syndrome Mentally retarded Heart disease Abnormal hands and feet Large eyes Large ears Normal lifespan Cat-Eye Syndrome 1 in 1,000,000 births 46 chromosomes XY or XX #22 Deletion of bottom arm Cat-Eye Syndrome Fused fingers and toes Mentally retarded Small jaw Heart problems Normal lifespan Four-Ring Syndrome 1 in 10,000,000 births 46 chromosomes XY or XX #4 Inversion Four-Ring Syndrome Cleft palate Club feet Testes don’t descend Short lifespan Down Syndrome 1 in 31,000 births 46 chromosomes XY=97% XX=3% #14/21 Translocation Down Syndrome Trisomy 1 in 1,250 births 47 chromosomes - XY or XX #21 Trisomy Nondisjunction Down Syndrome Short, broad hands Stubby fingers Rough skin Impotency in males Mentally retarded Small round face Protruding tongue Short lifespan Edward’s Trisomy Syndrome 1 in 4,400 births 47 chromosomes XX=80% XY=20% #18 Trisomy Nondisjunction Edward’s Trisomy Syndrome Small head Mentally retarded Internal organ abnormalities 90% die before 5 months of age Jacob’s Syndrome 1 in 1,800 births 47 chromosomes XYY #23 Trisomy Nondisjunction Jacob’s Syndrome ? Normal physically Normal mentally Increase in testosterone Acne Normal lifespan Klinefelter Syndrome 1 in 1,100 births 47 chromosomes XXY only #23 Trisomy Nondisjunction (sometimes seen as Kleinfelter) Klinefelter Syndrome Scarce beard Longer fingers and arms Sterile Delicate skin Low mental ability Normal lifespan Triple X Syndrome 1 in 2,500 births 47 chromosomes XXX only #23 Trisomy Nondisjunction Triple X Syndrome Normally physically Normal mentally Tall Fertile normal lifespan This is a cell after it has been broken open. A photo is taken of this and then manipulated on a computer. Each chromosome is cut out of the