Mendelian Genetics

1. Mendelian Genetics

2. Organisms inherit genetic information in a variety of ways that result in continuity of structure and function between parents and offspring • Coded instructions called Genes are passed on from parent to offspring • Remember: Genes are specific sequences of DNA that code for a protein.

3. Basic Genetic Terminology 1. Genetics – study of heredity 2. Heredity – passing of traits from parent to offspring 3. Offspring – young 4. Characteristic – a category , identifies group 5. Trait – any type of characteristic that can be passed from parent to offspring. ++++++

4. Basic Genetic Terminology 6. Paternal – father (or from father’s side) 7. Maternal– mother (or from mother’s side) 8. “N”= number of chromosomes 9 Haploid– N (half the amount of DNA or chromosomes) Sex cells 10. Diploid – 2N (the full amount of DNA or chromosomes) Ex: skin and blood cells (autosomal cells)

5. Locus for gene B Locus for gene A Chromosomes from sperm from egg (paternal) (maternal) • 11. Locus-the specific place of a gene • 12. Allele- different forms of a gene for the same trait. Homologous pair of chromosomes

6. Gregor Mendel The “Father of Genetics” • Austrian monk in mid 1800s • Studied the inheritance of traitsin pea plants • Developed the laws of inheritance • Mendel’s work was not recognized until the turn of the 20th century • Fertilized pea plants with different traits

7. Gregor Mendel Why peas? • 1. Control mating (self- vs. cross-pollination) • 2. Many varieties available • 3. Short generation time

8. Cross-pollinated pea plants: Took pollen from one plant brushed it onto another plant Observed the new offspring Fertilized peas with different traits Characteristic (categories) vs Traits (possibilities) Mendel’s Experiments

9. Experiment: Procedure

10. Observations Characteristics (observable physical feature)-Pea color Traits - yellow or green True breeding organism -purebred, produce offspring identical to themselves P = parental generation Parent 1: Pure yellow seed Parent 2: Pure green seed How did this happen?

11. Hybrid offspring – mixed with different traits F= filial means offspring F1 (First filial) generation= All offspring's are yellow pea color How did this happen? F2 (second filial) generation, F1 offspring = 3 are yellow, 1 is green What is the ratio? 3:1 How did this happen?

12. Results of Mendel’s Experiments F2 generation were all a 3:1 ratio

13. Mendel • Determined that traits are inherited in specific, predictable ratios • Worked with large numbers of offspring and contrasting traits • Determined that offspring receive inheritable “factors” from the parents that produce characteristics • What he called “factors” we now call “genes”

14. Mendel’s Conclusions • Genes are passed down from generation to generation • Inherit two copies of each gene- 1 from each parent • Different forms of genes are called alleles • Ex: Gene = plant height Allele = Tall Allele = Short Comes from dad (sperm) Comes from mom (egg)

15. With no knowledge of genes, chromosomes or DNA, Mendel developed three genetic principles that still exist today. These are Mendel’s Laws: • Law of Dominance • Law of Segregation • Law of Independent Assortment

16. Mendel’s Principles • Law of Dominance - When different factors exist for the same trait, only one factor appears Example: Purple Flowers X White Flowers = All Purple Flowers

17. Mendel’s Conclusions • Principle of dominance: • Some alleles are dominant; some alleles are recessive • Dominant ALWAYS covers recessive EX: Tall stem plant is dominant over short stem plant. That’s why the new plant was tall! Dominant assign letters: Capital T Recessive assign letter: lower case t

18. Homozygous 2 copies of the same allele AA, aa, TT, ZZ, zz Heterozygous One copy of each allele Aa, Tt, Zz Homozygous versus Heterozygous

19. For example: Purple flowers vs white flowers • Dominant (P allele), Recessive (p allele) • Parental generation is pure bred: Homozygous • Homozygous dominant (PP) Purple flower • homozygous recessive (pp) white flower • Offspring is hybrid: Heterozygous2 different alleles (Pp) Purple flower

20. Genotype versus Phenotype A. GENotype (Type o’ Genes) • An individual’s GENetic make-up • An individual’s alleles • Example: PP, Pp, OR pp • A heterozygote will be a carrier for a recessive allele. Carriers may be unaware that they carry a recessive allele until they have children. B. PHenotype • An individuals PHysical traits • The physical appearance resulting from an individual’s genetic make-up • Example: Purple flowers OR White flowers

21. Genotype versus Phenotype

22. Mendel’s Principles 2. Law of Segregation • Only one set of factors is passed on to the offspring (now explained by meiosis) Only one set of the original genes will get passed to the next generation

23. Law of Segregation Gene: Eye Color Blue eye allele Blue eye allele • Mendel concluded: • the short allele was separated from the tall one. • Segregation = when alleles separate during formation of gamete (sex cell) and randomly unite at fertilization (reproduce). • One allele comes from the egg, one allele comes from the sperm Blue eye allele Blue eye allele

24. What meiosis process relates to Mendels law of segregation? Separation of homologous chromosomes

25. Mendel’s Principles Mendel stated that reproductive cells have only one factor for each inherited trait. • This is proven by meiosis • Haploid cells are produced by meiosis

26. Segregate and Inheritance

27. Mendel’s Principles 3. Law of Independent Assortment • The factors that are passed on from parents to offspring are random or inherited independentlyof one another • allele pairs separate independently during the formation of gametes

28. Law of Independent Assortment Example: Peapodshape different from Peapod color

29. Mendel’s Principles 3. Law of Independent Assortment • Why true? Meiosis dynamics • Homologous chromosomes forms pairs without consulting each other and various arrangements are equally likely to align

30. Dominant vs Recessive • Dominant – the “stronger” of the 2 alleles • Given a capital letter • Example: T = tall • Trait always seen if present • Example: TT = tall plants AND Tt = tall plants • Recessive – gene shows up less often, not seen if the dominant allele is present • Given a lower case letter (use the same letter as the dominant gene) • Example: t = short • Trait only seen if individual is homozygous recessive • Example: tt = short plants BUT Tt = tall plants

31. Mate 2 Homozygous dominant plants • Two dominant alleles = dominant trait will show Ex: Tall plant x Tall plant  Tall plant TT alleles TT alleles TT allele

32. Monohybrid Cross- 1 trait Ex.Plant Stem Height Allele for Tall Plants Allele for Short plants TEST CROSS: TT TT T TT Segregate alleles- female on one side of Punnett square and male on the other side TT TT T TT Offsprings: Genotype is genetic make up: TT (100%) Phenotype is physical traits: Tall (100%)

33. Mate Dominant vs. Recessive • One dominant mates with one recessive = dominant trait will show Ex: Tall plant x short plant  Tall plant (hybrid) tt alleles Tt alleles TT alleles

34. Punnett Square- Device for predicting offspring from a cross. Make a grid, fill in grid, fill in offspring. Test cross: TT x tt Tt offspring Tt offspring Tt offspring Tt offspring Offsprings Results Genotype: Tt (100%) Phenotype: Tall (100%)

35. Mate 2 Homozygous Recessives • Two recessive alleles = recessive trait will show Ex: short plant x short plant  short plant tt alleles tt alleles tt alleles

36. Punnett Square-Test cross: tt x tt ttoffspring ttoffspring ttoffspring ttoffspring Offsprings Results Genotype: tt (100%) Phenotype: short (100%)

37. Punnett Square • Steps: • Determine which trait is dominant and which trait is recessive • Assign a capital letter for the dominant trait (usually the letter chosen is the first letter of the dominant trait) • Assign a lower case letter for the recessive trait (use the same letter • Determine the genotypes and gametes of each parent • Draw a Punnett Square (square divided into 4) • Write one parent’s gametes across the top and the other parent’s gametes across the side • Fill in the Punnett Square

38. Recessive phenotype with known genotype Dominant phenotype with unknown genotype RRorRr X rr If unknown genotype is Rr, then 50% of offspring should be red and 50% white If unknown genotype is RR, then all of the offspring should be red r r r r R R r R All Rr 50% Rr, 50% rr Testcross • How do you determine the genotype of an organisms with a known phenotype?

39. The offspring of a test cross can reveal the genotype of a parent • Depending on the number of traits involved(one, two, three) these crosses are: • Monohybrid cross • One trait studied, e.g. plant color • Dihybrid cross • Two traits studied, e.g. plant colorand plant height • Trihybrid cross • Three traits studied, e.g. coatcolor, length, and flower position.

40. Monohybrid Cross (Seed color) F2 generation- mate hybrids Genotype- genetic makeup Order: 1 YY, 2 Yy, 1yy or genotypic ratio 1:2:1 (HD:Het:HR) Phenotype- physical traits Order: 3 Yellow, 1 Green or phenotypic ratio 3:1 (Dominant: Recessive)

41. What about crossing 2 yellow heterozygous peas? Parent Phenotypes: Yellow and Yellow Parent Genotypes: Yy and Yy Yy What if we wanted these in a Ratio? Y y YY Yy Y YY Yy yy Genotypes: 25% YY, 50% Yy, 25% yy Yy y Yy yy Yellow (pure) Yellow (hybrid) Green (pure) 75% Yellow, 25% Green Phenotypes:

42. The End

43. Let’s say you are going to cross a homozygous dominant yellow skin lizard with a homozygous recessive green lizard yy Sperm Egg YY yy y y Y Yy Yy YY Y Yy Yy Yy Yy Yy Yy

44. Punnett Squares 1905, Reginald Punnett, an English biologist, devised the shorthand way of finding the expected proportions of possible genotypes in the offspring of a cross Used to predict the possible genotypes of offspring In reality, you don’t get the exact ratio of results shown in the square

45. Punnett Square-Monohybrid Cross

46. Punnett Square

47. Trait: Seed Shape Alleles:R– Roundr– Wrinkled Cross:Round seeds x Round seeds RRx Rr Monohybrid Cross Genotype:RR, Rr Phenotype: Round GenotypicRatio:1:1:0 PhenotypicRatio: All alike R r RR Rr R R RR Rr 48

48. Trait: Seed Shape Alleles:R– Roundr– Wrinkled Cross:Wrinkled seeds x Round seeds rrxRr Monohybrid Cross R r Genotype:Rr, rr Phenotype: Round & Wrinkled G. Ratio:0:1:1 P.Ratio: 1:1 Rr rr r r Rr rr 49

49. Genes are found where?

50. Chromosomes REMEMBER: genes control traits