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Genetics

Genetics. I. Foundations. Principles Developed by Mendel w/o knowledge of genes or chromosomes (“heredity factors”) Developed principles of dominance, segregation and independent assortment by analyzing pea plants. I. Foundations. Gene – Chromosome Theory

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Genetics

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  1. Genetics

  2. I. Foundations • Principles • Developed by Mendel w/o knowledge of genes or chromosomes (“heredity factors”) • Developed principles of dominance, segregation and independent assortment by analyzing pea plants

  3. I. Foundations • Gene – Chromosome Theory • Using Drosophila (fruit flies), scientists linked chromosomes and their migration during meiosis to traits, called genes • Genes are found at specific locations on chromosome • Allele – the gene for a trait • Homologous Chromosomes – pair of chrom that control the same traits (may not have the same genes)

  4. II. Genetic Concepts • Dominance • Dominant Allele • The ONE gene of a pair that expresses it’s trait, (T) • Recessive Allele • The OTHER gene that doesn’t show trait (t) • Homozygous • Both genes of the pair are the same (TT or tt) • Heterozygous (hybrid) • Both genes are different (Tt)

  5. II. Genetic Concepts • Phenotype • Physical appearance of individual • Genotype • Genes of individual

  6. T t T t T t T t T T T t T t t t II. Genetic Concepts T T • Mendel’s Pea Plant F1 (First Generation) Cross TT x tt t t • G: 100% Tt • P: 100% Tall T t • F2 (Second Generation) • Cross Tt x Tt T t • G: 25% TT, 50% Tt, 25% tt • P: 75% Tall, 25% Short

  7. II. Genetic Concepts • Segregation and Recombination • When gametes are formed (meiosis) chromosomes separate RANDOMLY • After fert, alleles (chrom) recombine, generally forming NEW combinations

  8. T t T t ? t ? t II. Genetic Concepts • After large # of crosses • Phenotype = 3:1 (75% tall, 25% short) • Genotype = 1:2:1 (25% TT, 50% Tt, 25% tt) • Genotype of Dominant Individual (T?) • Cross with recessive ind • If offspring show trait, parent was Tt t t T ?

  9. II. Genetic Concepts • Intermediate Inheritance • Traits are NOT clearly dom/rec (mixture of traits) • Codominance • BOTH dominant traits are expressed in hetero individual • Coat color in Roan cattle • RR = Red coat • WW = White coat • RW = Roan (mixture of red and white hairs)

  10. RR RW RW RW RW RW WW RW II. Genetic Concepts R R F1 = RR x WW W W • G: 100% RW • P: 100% Roan R W • F2 = RW x RW R W • G: 25% RR, 50% RW, 25% WW • P: 25% Red, 50% Roan, 25% White

  11. II. Genetic Concepts • Incomplete Dominance • Heterozygous ind is a mixture (half way) between both homozygous parents • RR = Red snapdragon WW = White RW = Pink

  12. II. Genetic Concepts • Independent Assortment • If genes for TWO different traits are on DIFFERENT chromosomes, they are inherited INDEPENDENTLY of each other • Gene Linkage • If genes for TWO different traits are on the same chrom pair, they are linked (inherited together)

  13. II. Genetic Concepts • Crossing Over • During meiosis, pairs of chroms can twist around each other, break, exchange segments and rejoin (swap parts) • Gives a rearrangement of linked genes, increases variability of offspring

  14. II. Genetic Concepts • Multiple Alleles • Human Blood type is determined by 3 alleles (IA, IB or ii) • IA and IB are codominant and “i” is rec to both IA and IB • Blood Type • A = IAIA or IAi • B = IBIB or IBi • AB = IAIB • O = ii

  15. IAIB IAIB IBi IBi IAIB IAi IBi ii II. Genetic Concepts IA i IAi x IBi IB i • G: 25% IAIB • 25% IAi • 25% IBi • 25% ii • P: 25% AB • 25% A • 25% B • 25% O IA i • IAi x IBIB IB IB • G: 50% IAIB, 50% IBi • P: 50% AB, 50% B

  16. II. Genetic Concepts • Sex Determination • Two types of chromosomes in humans • Autosomes = 22 pairs (44 chroms) • Sex Chrom = 1 pair (2 chrom) • Sex Chromosomes • X and Y • XX = female, XY = male • Sex of offspring is determined by the gene in the sperm (either X or Y)

  17. XX XY XX’ X’Y II. Genetic Concepts • Sex Linked Genes • Genes for some traits are on X chromosome • Most SL are recessive and appear more often in males • Hemophilia and Color Blindness X Y X X’

  18. III. Mutations • Random changes in genetic material • MUST be in sex cells to get passed on to offspring • Body cell mutations ONLY effect ind, cannot be passed on • Some are obvious (albino), others not easily noticed • MOST are harmful (depends on mutation and type of environment

  19. III. Mutations • Types • Change in Number • Sometimes in meiosis, a pair of chromosomes do NOT separate (non-disjunction), making gametes with > or < normal #. • If these gametes are fert, zygote can have > or < 2n number • Downs Syndrome – extra 21st chrom • Plants CAN be polyploid (3n or 4n), makes larger or more vigorous, some are sterile (seedless) • Change in Structure • Breaking or recombining parts

  20. III. Mutations • Mutation rate can increase with: • Radiation (X-rays, UV rays) • Chemicals (formaldehyde, asbestos)

  21. IV. Human Heredity • Difficult to study humans because: • Generation time is too long (40 weeks) • Small # of offspring • Unethical to perform exp on humans • Pedigree Charts • Trace a trait through family for generations • Shows presence / absence of trait • Can identify carriers of rec genes

  22. V. Heredity and Environment • Phenotype can be influenced by env (nutrients, sunlight, temperature) • Himalayan Rabbit • Temp affects fur color • Plants need sunlight to make chlorophyll.

  23. VI. Plant and Animal Breeding • Artificial Selection • Desirable Traits (sheep w/ thick, soft wool) are crossed hoping the offspring will have the traits • Inbreeding • Mating closely related organisms to make more w/ desirable traits • Increases chances of harmful rec genes to be inherited and cause disorders

  24. VI. Plant and Animal Breeding • Hybridization • Crossing 2 individuals w/ diff traits in hope offspring will have both traits • Rose w/ large petal X Rose w/ nice smell hopefully = Rose w/ large petal and nice smell

  25. VII. Genetic Disorders • Detected before / after birth • Techniques • Screening – analysis of blood, urine • Amniocentesis – analysis of fluid around baby • Karyotyping – picture of paired chroms

  26. VII. Genetic Disorders • Sickle – Cell Anemia • Rec blood disorder • Mutated gene causing abnormal hemoglobin and RBC • RBCs don’t carry O2 well b/c of different shape

  27. VII. Genetic Disorders • Tay–Sachs • Rec disorder (fatal) • Nerve tissue in brain breaks down b/c of build up of fatty material • Body cannot make enzyme to break down the fat

  28. VII. Genetic Disorders • Phenylketonuria (PKU) • Rec disorder • Body cannot make enzyme to break down aa phenylalanine • Causes mental retardation • Detected by urine analysis or amniocentesis • Can be prevented by diet

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