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Ch 13 Patterns of Inheritance

Ch 13 Patterns of Inheritance. 1. 13.1 Heredity and Environment. Nature vs Nurture? Trait = Something about an organism you can describe or measure Characteristic = Typical or distinctive Phenotype = The trait(s) you observe Genotype = What’s in the DNA

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Ch 13 Patterns of Inheritance

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  1. Ch 13Patterns of Inheritance 1

  2. 13.1 Heredity and Environment Nature vs Nurture? Trait = Something about an organism you can describe or measure Characteristic = Typical or distinctive Phenotype = The trait(s) you observe Genotype = What’s in the DNA Phenotype = Genotype + Environment Both are important! 2 See P. 344 for more examples

  3. Peas Easy to grow Easy to control crosses Short lifespan Mendel’s Experiment (ca. 1860) True breeding plants Binomial Traits Either/Or Traits Thousands of plants and crosses Careful data analysis 13.2 Mendel, Peas, and Alleles 4 Augustinian Monastery of St. Thomas at Brno Father of Modern Genetics

  4. Mendel’s 7 Pea Traits5 See P. 346

  5. 9 Pea Breeding by Mendel Or “How to control pea sex”

  6. 13.3 Genes and Chromosomes Bacterial Genome One circular chromosome + Plasmids 90% of DNA is coding DNA (translated) 6 Eukaryotic Genome Many chromosomes 1% of DNA is translated Purpose of 99% ?? 5

  7. Making a Karyotype22 1. Cells arrested in metaphase 2. Special procedures and stains added to produce banding patterns 3. Chromosomes identified by - Banding - Length of arms - Centromere position Is this individual male or female? Autosomes = Non-sex chromosomes

  8. 13.4 Probability and Genetics Probability: mathematics used to predict the chance (probability) that an event will happen. Eg. p(heads) = probability of heads on a coin toss = ½ = 0.5 So… If you toss a coin 10 times, you’d expect to see 5 heads. The larger the sample size, the more accurate the prediction. 8 7

  9. Basic Probability Laws Independent Events: one occurring DOESN’T change the probability of the other happening (http://www.stat.wvu.edu/SRS/Modules/ProbLaw/AndProb.html) The “And” Rule: p(A and B) = p(A) x p(B) Eg. What are the chances of tossing a head then a tail? Mutually Exclusive and Independent: one occurring means the other DOESN’T (http://www.stat.wvu.edu/SRS/Modules/ProbLaw/OrProb.html) p(A and B) = 0 The “Or” Rule: p(A or B) = p(A) + p(B) Eg. What are the chances of drawing a heart and a spade in one draw? What are the chances of drawing a heart OR a spade?

  10. 13.5 Inheritance of Alleles9 Monohybrid Cross: True breeding plants in one trait crossed together. P = Parental Generation F1 = First Filial Generation F2 = Second Filial Generation Truebreeding = Homozygous Genotype: pp or PP Hybrid = Heterozygous Genotype: Pp

  11. Anatomy of a Chromosome20 Homologous Pair Different allele = slightly different version of same protein = different phenotype of specific trait

  12. From Allele to Phenotype5 Remember the Central Dogma Gene Product + Environment = Phenotype

  13. Classic Monohybrid Cross Ratios! How do the And and Or rules apply? 9

  14. Phenotypic and Genotypic Ratios9

  15. Alleles Meiosis Fertilization Diploid zygote (contains paired alleles) Diploid cell (contains paired alleles, alternate forms of a gene) Haploid gametes (allele pairs separate) Mendel’s Basic Laws Principle of Segregation:Each gamete receives ONE allele for a given trait. Visual Summary 9.1

  16. Principle of Independent Assortment:Alleles for a trait assort or separate (during meiosis) into different gametes independently. Consider homozygous yellow, round peas crossed with green wrinkled peas. What would you expect if color and shape are independent choices?? So… the number of possible gamete genotypes = product of the number of alleles for each trait You can also apply the And and Or Rules

  17. The Dihybrid Cross and Independent Assortment9 Why’s it called a dihybrid cross? Mendel’s experiments showed the 9:3:3:1 ratio, clearly supporting the hypothesis of independence.

  18. Green-wrinkled seeds (yyrr) Yellow-round seeds (YYRR) P Generation Meiosis Fertilization Gametes F1 Generation All round yellow seeds (RrYy) Principle of Independent Assortment: Follow both the long and the short chromosomes. Principle of Segregation: Follow the long chromosomes (carrying R and r) taking either the left or right branch. Meiosis They are arranged in either of two equally likely ways at metaphase I. Metaphase I (alternative arrangements) The R and r alleles segregate in anaphase I of meiosis. They assort independently, giving four gamete types. Only one long chromosome ends up in each gamete. Metaphase II Gametes Fertilization recombines the r and R alleles at random. Fertilization results in the 9:3:3:1 phenotypic ratio in the F2 generation. Fertilization among the F1 plants F2 Generation Figure 9.23

  19. Using a Test Cross…9 You’re forming and testing a hypothesis!

  20. 13.6 Sex Determination9 MammalsDrosophila melanogasterSome Plants Spinach, date palms GrasshoppersCricketsCockroaches BirdsSome FishSome Insects Most plants and some animals have NO sex chromosomes

  21. Incomplete Dominance9 13.7 Alleles without Dominance

  22. Codominance10 Antibodies attack the cells with the type of protein that doesn’t belong.

  23. Multiple Alleles Like the human blood groups… more than two possible alleles. Polygenic Inheritance More than one gene involved. P Generation AABBCC (very dark) aabbcc (very light) F1 Generation AaBbCc AaBbCc F2 Generation Sperm Eggs Figure 9.22 Other Patterns of Inheritance9 See P. 364 for Multifactorial traits (includes environmental factors)

  24. Pleiotropy Multiple Traits – Eg. Sickle Cell Single gene Polygenic inheritance Single trait (e.g., skin color) Multiple genes

  25. 11 Coat Colors in Cats 12 14 15 13

  26. When Mendelian ratios aren’t what you see… • In 1908, British biologists discovered an inheritance pattern inconsistent with Mendelian principles (a) Experiment: Purple flower PpLl PpLl Long Pollen Figure 9.24a

  27. (b) Explanation: Linked genes Parental diploid cell PpLl Meiosis Most gametes Fertilization Egg Sperm Most offspring 3 purple long : 1 red round Not accounted for: purple round and red long Figure 9.24b Genes on the same chromosome Can’t be completely independent Parental Genotypes: are the most common – just like parents Recombinant Genotypes: require crossover during meiosis.

  28. Forming Recombinant Gametes Tetrad Crossing over Are you more or less likely to cross-over between genes if the genes are farther apart? Tetrad Parental-type gametes Fertilization Purple round Red long Among the offspring, some with recombinant phenotypes Figure 9.24c

  29. Chromosome Mapping9 Can use crossing-over frequencies to determine where on the genes are on a single chromosome See P. 361 for examples in humans

  30. Male Female Male Female Male Female XRXR XrY XRXr XRY XRXr XrY All females inherit two X chromosomes, one from each parent. Female Female All males inherit one X chromosome, always from the mother. R = red-eye allele r = white-eye allele Male Male (c) Heterozygous female white-eyed male (b) Heterozygous female  red-eyed male (a) Homozygous red-eyed female  white-eyed male Figure 9.29 13.9 X-Linked Traits • ~ 300 X-Linked traits in humans • Hemophilia • Red/Green Color Blindness Is the X-linked trait more common in males or females? Why?

  31. Barr Bodies in Females17 In development, only one random X chromosome remains active in each cell, so females have a mix of genes expressed… Each color patch arose from a specific cell.

  32. Cats are not peas…  23

  33. Meiosis I Nondisjunction Meiosis II Nondisjunction Gametes n - 1 n - 1 n - 1 n n + 1 n + 1 n + 1 n Number of chromosomes (a) Nondisjunction in meiosis I (b) Nondisjunction in meiosis II Figure 8.21 13.10 Nondisjunction9 When chromosomes don’t separate right, weird things happen! See P. 363 for a specific example in fruit flies

  34. Results of Nondisjunction Egg cell n + 1 Sperm cell Zygote 2n + 1 Figure 8.22 n (normal)

  35. Examples of Nondisjunction Down Syndrome: Trisomy 21 Mental retardation, facial feature change, short stature, heart problems Poor beard growth Breast development Web of skin Constriction of aorta Poor breast development Under- developed testes Under-developed ovaries 17 (a) A man with Klinefelter syndrome (XXY) (b) A woman with Turner syndrome (XO) Figure 8.23

  36. Sources Cited 1. www.roslin.ac.uk/research/ animal.html 2. www.myangel.com/taf.shtml 3. http://www.acad.swarthmore.edu/bio5/tong/Gene%20Basics/the_history_of_gene_testin.htm 4. http://www.library.villanova.edu/html2/lib/mendel/mendexhib.htm 5. http://www.emc.maricopa.edu/faculty/farabee/BIOBK/BioBookTOC.html 6. cellbio.utmb.edu/cellbio/ nucleus2.htm 7. www.pbs.org/wgbh/nova/ israel/familyy.html 8. www.valottery.com/ scratchers.htm 9. BioCD. From Biology, Fifth Edition. Campbell, Reece, Mitchell. Addison, Wesley, Longman. 1999. 10. http://gslc.genetics.utah.edu/units/basics/blood/types.cfm 11. http://www.fanciers.com/other-faqs/color-genetics.html#intro 12. http://www.cfainc.org/breeds/profiles/siamese.html 13. www.squirrel.com.au/~tonkinese/ loral2.html 14. http://www.cfainc.org/breeds/profiles/burmese.html 15. members.shaw.ca/ purrsia/p2.html 16. http://www.accessexcellence.org/AB/GG/ 17. faculty.uca.edu/~johnc/ gener1440.htm 18. http://fig.cox.miami.edu/Faculty/Dana/turner.jpg 19. http://fig.cox.miami.edu/Faculty/Dana/klinefelter.jpg 20. http://www.lifesci.utexas.edu/faculty/sjasper/images/0904.gif 21. http://www.blc.arizona.edu/courses/181gh/rick/genetics1/monohybrid.html 22. http://www.ucl.ac.uk/~ucbhjow/medicine/mendel.html 23. Bioshow: for Biology: Concepts and Connections, Second Edition. Campbell, Mitchell, and Reece

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