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Human Genetics Human Genetics I. Mutations= changes in DNA a. Germ Cell Mutations– occurs during meiosis; takes place in sex cells b. Somatic Mutations take place in the body cells c. Mutations increase the amount of variation among offspring. II. Gene Mutation=Changes in Nucleotides of DNA a. Point Mutations (2 types) 1.Base –pair substitutes: may have no effect, change amino acid; or change to stop codon 2.Frameshift Mutations • Base-pair insertion or deletion • Result is a nonfunctional protein • Alters the reading frame of mRNA triplets III. Chromosome Mutations A. B. C. D. Deletion: removal of a chromosomal segment Duplication: repeats a chromosomal segment Inversion: segment reversal in a chromosome Translocation: movement of a chromosomal segment to another non-homologous chromosome IV. Causes of Mutations A. Chance B. Mutagen = environmental factor damages DNA Ex. UV light (sun; skin cancer), cigarette tar, asbestos, virus, radiation V. Karyotypes A. Shows chromosomes paired by size, shape, and appearance in metaphase. B. Cells are treated, photographed, sorted and arranged by homologous pairs. C. Chorionic villi sampling, and amniocentesis can be used to diagnose chromosomal abnormalities. VI. Changing Chromosome Number A. Nondisjunction = failure of chromosomes to separate during Prophase I of meiosis;addition or loss of a chromosome B. Monosomy occurs when only one of a pair is present (45) C. Trisomy occurs when three of a particular type of chromosome is present (47) D. Nondisjunction Abnormalities 1. 2. 3. Many trisomies and nearly all monosomies are fatal. XYY males (Jacob syndrome)- tall, acne, not overly aggressive XO females (Turner syndrome)- short, webbed neck, no puberty. Turner syndrome affects approximately 1 out of every 2,500 female live births worldwide. It embraces a broad spectrum of features, from major heart defects to minor cosmetic issues. Some individuals with Turner syndrome may have only a few features, while others may have many. Almost all people with Turner syndrome have short stature and loss of ovarian function, but the severity of these problems varies considerably amongst individuals. E. Trisomy = Extra chromosomes (47) 1. Klinefelter Syndrome = XXY; male, some retardation, low fertility (rare cases (48,XXXY) or (49,XXXXY) 2. Triple X Female (XXX) – no physical abnormalities 3. Fragile X Syndrome – X chromosome broken; males; hyperactive or autistic, delayed speech 4. Down Syndrome = extra 21st chromosome; mental retardation, fold of skin above eyes, weak muscles VII. Sex Determination A. A. Thomas Hunt Morgan 1. Experiments with Drosophila (fruit fly) 2. Sex Chromosomes Determine Gender B. B. Autosomes are non-sex chromosomes C. (22 pairs) D. C. Sex chromosomes differ between males and females. 1. Human female is XX 2. Human male is XY. (#23) D. Sex chromosomes carry genes for traits unrelated to sex. E. Single, recessive allele on X expressed F. Males express sex-linked alleles more G. Example of Sex Link Traits Color Blindness Hemophilia – blood doesn’t clot x H x h = normal x Hy = normal H H x x = normal x h y = hemopheilia XhXh = hemophilia VIII. Human Genetics Traits A. Single Allele Traits 1. Sickle Cell Anemia a. Sickle shaped red cells b. Clump; block arteries, lack 02, pain, weakness, death c. AA= normal cell AA’= both kinds; protected from malaria A’A’= sickle cells 2. Huntington’s Disease a. b. c. Cause by one dominant allele Brain cells degenerate; no muscle control; death Occurs at 30 -40; passed to child 50% of time H h h h Hh hh Hh hh 3. Tays-Sacs, Cystic Fibrosis, Phenylketonuria,Dwarfism Tays Sachs Disease is an inherited incurable disease of the central nervous system. Its symptoms first appear when a baby is about 6 months old. The baby stops smiling and developing through the normal developmental stages. Blindness and paralysis follow within the next four years resulting in the child's death by the age of five years. Most babies die within the first two years. B. Polygenic Traits = 2 or more genes control trait 1.Skin color - 4-7 genes with additive effect of amount of melanin 2. Eye Color – blue (light melanin), brown (lot of melanin) 3. Height C. Multiple Allele Traits = Trait with 3 or more alleles; only get 2 1. ABO Blood group system; types – A, B, AB, O 2. AA =type A AO = type A OO = type O BB= type B BO = type B AB= type AB *A,B codominant *Both dominant to O D. Sex Influenced Traits = not a sex chromosomes; influenced by sex hormones 1. B=Baldness; dominant in males and recessive in females 2. BB=bald females and males 3. BB” – female will not lose her hair 4. BB” – male will lose hair IX. Studying Humans A. Population Sampling = select a number to represent whole population B. Twin Studies – environment vs. genetics C. Pedigree Studies – family chart of traits D. DNA fingerprinting = study the patterns of bands obtained from electrophoresis 1. Gel electrophoresis – process to separate DNA fragments by size of charge IN: P 34 Contrast 2 types of point mutations. OUT: P34 Mutations occur at 2 levels. What are they? IN: P 36 A new species has been discovered. The organism has 18 chromosomes. How many chromosomes would the new species have if a monosomy occurred? …a trisomy? OUT: P36 Hemophilia is a sex linked disease. Cross a normal male with a female that is a carrier of the disease. What percent of the males will have hemophilia? IN: P 38 What do you know about sickle cell anemia? OUT: Explain polygenic traits in your own words. How would an albino occur?