Genetics

2. Genetics • Study of inheritance, the stability and variance of inheritance patterns • Gregor Mendel, “The Father of Genetics” • Worked with the garden pea plant using cross pollination • What would happen if we all had the exact same DNA sequences? What if we had extremely divergent DNA sequences? • What determines which genes we inherit from our mother and father?

3. Genetic Terms • Gene-basic unit of inheritance, arranged in a linear sequences on a chromosomes • Allele-alternative forms of a gene; alleles contain genetic information that is expressed as traits. • Examples of traits are flower color, seed shape, plant height etc. • Each trait can have a different version (allele); flower color can be purple or white, we use one letter for the trait flower color, but change whether it is upper or lower case

4. Genetic Terms • Dominant- 1 copy of allele results in expression of trait, always use a capital letter to show it is dominant, ex. A • Recessive-requires 2 copies of same allele to get expression of trait, always use lower case letter to show it is recessive, ex. a • If purple is dominant to white flowers, how would you write your alleles?

5. Genetic Terms • Homozygous Dominant-2 same copies of dominant allele, get expression of dominant trait, AA • Heterozygous Dominant-1 copy of dominant allele, 1 copy of recessive, still get dominant trait expression, Aa • Homozygous recessive-2 copies of recessive allele, get expression of recessive trait, aa

6. Genetic Terms • Genotype-genes of an organism • Phenotype-physical appearance of the organism True or False: The phenotype of an organism is dictated by the genotype of that organism • True breed lineage vs. hybrid offspring • P, F1, F2 Generation

7. Genetic Terms • Monohybrid cross-a cross that only predicts the genotype and phenotype for one trait, ex. plant flower color • Dihybrid cross-a cross that predicts the genotype and phenotype of 2 traits, ex. plant flower color and height

8. Predicting Gametes If an organism has the genotype BB, how many different gametes can it make? 1: B When predicting gametes, keep in mind that each gamete must have 1 complete set of instructions Cc DDEE GgHh 2: C, c 1: DE 4: GH, Gh, gH, gh KKLlMM TTUUVV AaBBCc 2 1 4

9. Mendel’s Early Genetic Experiments: Monohybrid Cross Crossed a true breed purple flower plant with a true breed white flower plant P generation PP x pp P-purple p-white Pp F1 generation, all purple heterozygous dominant Crossed the F1 generation with each other Pp x Pp F2 generation PP, Pp, Pp, pp Genotypic Ratio 1 PP: 2 Pp :1 pp Phenotypic Ratio 3 purple: 1 white

10. Mendel’s Law of Segregation • Mendel continued his monohybrid crosses (1000s) for 7 different traits • Average ratio for all traits studied was always about 3:1 • The Law of Segregation: • Each individual has 2 of every gene (alleles) for each trait • These genes (alleles) will separate from each other during meiosis into different gametes. • Fertilization gives each new individual 2 alleles for each trait

11. A a b B A B A b a B a b

12. Genetics Problem • In parrots, alleles for blue feathers are dominant to alleles for yellow. Cross a heterozygous dominant blue feathered parrot with a yellow feathered parrot

13. Monohybrid Genetics Problem B b b b Genotypic ratio 1 Bb : 1 bb Phenotypic ratio 1 Blue : 1 yellow

14. Genetics Problem • Rhinoceroses can be born without a horn, the recessive condition. • Cross 2 heterozygous dominant rhinoceroses. Can they produce a baby rhino without a horn?

15. Monohybrid Cross H-horn present h-no horn H h H h Genotypic Ratio 1 HH: 2 Hh : 1 hh Phenotypic Ratio 3 with horns : 1 no horn

16. Mendel’s Early Genetic Experiments: Dihybrid Cross • Mendel noticed that all purple flower plants were tall and all white flower plants were short • Could you ever see a purple short plant or a white tall plant? • Crossed a homozygous dominant tall purple flower plant with a homozygous recessive short white flower plant

17. Mendel’s Early Genetic Experiments: Dihybrid Cross P generation AABB x aabb F1 AaBb F2 AaBb x AaBb 4 by 4 punnett square Phenotypic ratio 9 purple, tall: 3 purple, short: 3 white, tall: 1 white, short

18. Mendel’s Early Genetic Experiments: Principle of Independent Assortment • The results from the many dihybrid crosses allowed him to develop the • Principle of Independent Assortment-gene pairs (traits) are independent of each other and are sorted into different gametes • Exception: Linked genes; they always sort together into same gamete

19. A a b B Diploid (2N) A B A b a B a b Haploid (1N)

20. Genetics Problem: Dihybrid Cross In panthers, black fur is dominant to yellow fur. A recessive gene results in the absence of claws. Predict the offspring of a cross between a heterozygous black panther with no claws and a yellow panther that is heterozygous for claws

21. Genetics Problem: Dihybrid Cross B-black fur b-yellow fur C-claws c-no claws bC bc Bc bc Genotypic Ratio 1:1:1:1 Phenotypic Ratio 1:1:1:1

22. Punnett Square and Probabilities • What is the probability from the following cross that any offspring will have unattached earlobes or attached earlobes? • The probability of inheriting a specific allele is like flipping a coin and occurs every time parents have an offspring

23. Mendel’s Early Genetic Experiments: Test Cross • If you have a purple flower, what are the possible genotypes? PP or Pp • How do you decide? Do a Test Cross using a white flower plant PP x pp = all offspring are Pp (purple) Pp x pp = ½ offspring are Pp (purple) ½ offspring are pp (white)

24. Human Genetics • The study of inheritance and prediction of genes in humans • Very difficult, many genes involved • Small sample size, few offspring • Mate by chance, live in diverse environments • Long life span makes it difficult to track genes in different generations

25. Human Genetics: Understanding a Pedigree • Pedigree-a chart of genetic connections between individuals; family tree that tracks genes/diseases • Single genes can be followed by constructing pedigrees • Square=male circle=female • Shaded =affected non-shaded=not affected • A line between a circle + square=mating • Lines from the mating=offspring

26. Human Inheritances Patterns • Autosomal Recessive Inheritance-gene is located on autosome; 2 copies of gene required for expression of disease/trait; 1 copy=carrier, not affected • Albinism, cystic fibrosis, sickle cell anemia, phenylketonuria, methemoglobinemia, Niemann-Pick disease

27. Effects of Autosomal Recessive Disorders

28. F-normal, no cystic fibrosis f-cystic fibrosis Autosomal Recessive Inheritance What are the chances of offspring from 2 heterozygote parents for the cystic fibrosis gene having the disease? Parents are carriers F f F f 25% (1 out of 4) will have cystic fibrosis What are the genotypic/phenotypic ratios?

29. Human Inheritances Patterns • Autosomal dominant inheritance- gene is located on autosome;1 copy of gene results in expression of disease/trait • Ex. Achondroplasia, Huntington’s, OsteogenesisImperfecta, polydactyly, progeria, sperocytosis

30. Autosomal Dominant Inheritance P-polydactyly (extra fingers/toes) p-normal What are the chances of offspring from a cross of 2 heterozygous parents for polydactyly also having the condition? P p P p 75% (3 out of 4) chance of having polydactyly What is the genotypic/phenotypic ratios?

31. Variations to Mendelian Inheritance Patterns: Multiple Alleles • Codominance • 2 alleles are not dominant to each other, and if both are present both are expressed • Ex. Blood Groups- ABO blood typing • A dominant to O, but not to B • B dominant to O, but not to A • O recessive

32. Codominance: Blood Typing • There are 6 genotypes that express 4 different blood phenotypes Phenotype Genotype • Type A AA, AO • Type B BB, BO • Type AB AB • Type O OO

33. Codominance: Blood Typing • What does a blood typing do? Why is blood called A, B, AB, or O? • Based on the different sugars found on red blood cells ex. Type A blood has A sugars on RBCs • What type of sugars does AB or O have? • Why do we need to type blood?

34. Codominance: Blood Typing Problems • Cross a person with type O blood with one that has type AB blood • Give phenotypic and genotypic ratios

35. Codominance: Blood Typing Problems O O A B Genotypic Ratio 1 AO : 1 BO Phenotypic Ratio 1 Type A : 1 Type B

36. Codominance: Blood Typing Problems Type B blood male and a Type O blood female never produce a Type O blood child. Is this possible? Why or why not?

37. Codominance: Blood Typing Problems Type B blood can be BB or BO* O O B B Genotypic Ratio All are BO Phenotypic Ratio All are Type B *this genotype would produce a Type O offspring

38. Blood Type Problem If father’s genotype is BO, it would be possible to get an O blood type child B O O O Genotypic ratio: 1 BO: 1 OO Phenotypic ratio: 1 type B: 1 type O blood

39. Variations to Mendelian Inheritance Patterns • Incomplete Dominance-one allele isn’t complete dominant to the other; heterozygotes are intermediate in phenotype • Snap dragon flower color: R-red, r-white • RR x rr = Rr all offspring are pink • What happens when 2 pink flower plants are crossed? Give phenotypic and genotypic ratios Rr Rr

40. Incomplete Dominance R-red r-white Rr-pink R r R r

41. Pleiotropy • Expression of alleles (for 1 trait) has positive or negative effects on other traits Ex. Sickle cell mutation • Affects the protein hemoglobin which carries O2 • Insufficient O2 will cause RBCs to sickle and eventually burst anemia • Secondary effectsheart/lung damage, kidney/heart failure, skull deformation, mental impairment

42. Pleiotropy: Marfan Syndrome • Single gene mutation affects 2 or more distinct and unrelated traits • mutation of fibrillin gene

43. Incomplete Penetrance • Polydactyly  extra fingers/toes • Autosomal dominant disorder which exhibits incomplete penetrance • A dominant allele sometimes does not determine the phenotype • Some who inherit polydactyly allele are phenotypically normal

44. Pleiotropy: Sickle Cell Anemia • Homozygous for condition die in early 40s, no cure, extremely debilitating • Severe anemia, poor circulation, physical weakness, impaired mental function, spleen damage • Why is this mutation maintained? • Protection/resistance against malaria S-no sickle cell s-sickle cell (recessive) • SS-no sickle cell, no resistance • Ss-no sickle cell, resistance • ss-sickle cell, resistance Heterozygote advantage

45. Sickle Cell Anemia Genetics Problem Cross 2 heterozygous dominant parents together. How many children would have sickle cell? How many children would not? How many children are resistant to malaria? How many are not?

46. Sickle Cell Anemia Genetics Problem Parents are Ss-do not have sickle cell S s S s 3 children do not have sickle cell, 1 does 3 children protected, 1 is not

47. Epistasis • When one gene pair masks/prevents another gene pair’s expression Ex. Labrador fur color • B-black fur b-brown fur • E-melanin deposited e-no melanin • The recessive genotype of “ee” will cause no melanin deposition, thus the resulting fur coat will be yellow, even when “B or b” alleles are present

48. Continuous Variation in Traits • Multiple genes are responsible for the phenotype of an organism  polygenic inheritance • Skin and eye color, height • A great deal of variation exists resembling a bell shaped curve • Look at human height; a few genes regulate height, but there exists a normal amount of variation • What factors contribute to height?

50. Environmental Effects on Phenotype: Multifactorial Traits • Fur color on Siamese cats or Himalayan rabbits-heat sensitive enzyme that produces melanin • Flower color on Hydrangea Plant-influenced by acidity of soil • Height of Yarrow plant cuttings-varies depending on elevation planted