Genetics, Heredity, Mendel and Punnett Squares

1. Genetics, Heredity, Mendel and Punnett Squares

2. Heredity: the passing of traits from parent to offspring • Genetics: the study of how traits are passed from parents to offspring How does it work?

3. Terms to Know • Characteristic: A feature that has different forms in a population • Example: Flower color • Trait: The different form of a characteristic that can be passed down to offspring • Example: Purple flower

4. Terms to Know • Gene: section of DNA that determines a trait • Allele: alternate form of a gene (represented by letters) (Mendel called them factors) • EX: plant size • “T” is the tall allele (dominant) • Dominant: Trait that masks another trait • “t” is the short allele (recessive) • Recessive: Trait that is masked by another trait

5. Term to Know • Punnet square - visual aid showing how traits are inherited in a cross (mating) t t T t

6. Terms to Know • Determined from Punnett Squares • Genotype - combination of alleles that an individual has. Example: TT, tt, Tt • The genes producing the phenotype • Phenotype - physical appearance of a trait (what you see)-Examples: tall, short, etc.

7. Homozygous and Heterozygous • Homozygous – having two of the SAME alleles • Heterozygous – having two different alleles • Carrier – an individual who carries the recessive allele but does not show it in their phenotype

8. Gregor Mendel (1822-1884) • Austrian Monk • Considered Father of Modern Genetics • Researched on Pisum sativum • Pea Plant

9. Background • Why peas were a good choice • Self-pollinating: Sperm from one flower fertilizes the egg of the same flower • Cross-pollinating: Sperm from one flower fertilizes the egg of a different flower

10. Pea plant characteristics, each with 2 contrasting traits • Studied one characteristic at a time • plant height: long or short stems • flower position along stem: axial or terminal • pod color: green or yellow • pod appearance: inflated or constricted • seed texture: smooth or wrinkled • seed color: yellow or green • flower color: purple or white

11. Mendel’s question • Mendel noticed that some purple-flowering plants grew from seeds collected from the purple-flowering plants, but some white-flowering plants also grew from the seeds of purple-flowering plants • He noticed that this also occurred with the other characteristics, such as plant height • WHY?

12. Mendel’s Experiment • To study this question, Mendel began to grow plants that were pure for each trait • Plants that are pure for a trait always produce offspring with that trait • Purebred: the offspring of many generations that have the same traits

13. TT TT TT TT tt tt tt tt Mendel’s Parental Cross TT x TT tt x tt t t T T T T t t Mendel generated “true breeding” (HOMOZYGOUS) plants by self-fertilizing (self-pollinating) tall plants and short plants.

14. Results of Parental Cross • Cross= TT x TT • Phenotype= All Tall • Genotypes= All TT • Phenotypic Ratio= 4:4 • 100% • Genotypic Ratio= 4:4 • 100% • Cross= tt x tt • Phenotype= All Short • Genotype= All tt • Phenotypic Ratio=4:4 • 100% • Genotypic Ratio= 4:4 • 100%

15. Mendel cross-pollinated tall plants with short plants (P generation), and noticed that all of the resulting offspring were tall – F1 generation. • He then took the tall offspring (F1 generation) and allowed them to self pollinate. About ¾ of the offspring were tall, and ¼ were short – F2 generation.

16. Tt Tt Tt Tt Mendel’s F1 generation… t t T T When Mendel crossed a “true breeding”(homozygous) tall plant and a “true breeding”(homozygous) short plant, he found that all of the offspring were tall. He called this his First Filial or F1 generation.

17. TT Tt Tt tt Mendel’s F2 generation… T t T t When Mendel allowed the F1 generation to self-fertilize, he found that¾of the resulting plants were tall and ¼ were short (3:1 ratio). He called this his Second Filial or F2 generation.

18. F1 Results • Crossed a true breed tall with a true breeding short plant • Cross: TT x tt (Tall x short) • Phenotype: All Tall • Phenotypic Ratio= 4:4 (100%) • Genotype: All Tt • Genotypic Ratio= 4:4 (100%) • Back

19. F2 Results Cross= Tt x Tt • Genotypic Ratio= TT 1:4 (25%) • Genotypic Ratio= Tt 2:4 (50%) • Genotypic Ratio= tt 1:4 (25%) • Phenotypic Ratio= Tall 3:4 (75%) • Phenotypic Ratio= Short 1:4 (25%)

21. Mendel’s Results and Conclusions • This led Mendel to hypothesize that something within the pea plants controlled the characteristics he observed—he called these controls factors. • A pair of factors controls each trait – we call these alleles

22. Recessive vs. Dominant Traits • Follow 1 trait: • P generation: present • F1 generation: absent • F2 generation: present • Absence in the F1 generation was controlled by a dominant allele • it masked, or dominated, the other factor • The trait that was absent in the F1 generation but was controlled by a recessive allele.

23. Genes and Alleles • Letters are used to represent alleles • Capital letters refer to dominant alleles • Lowercase letters refer to recessive alleles P= dominant flower color, purple p= recessive flower color, white Y= dominant seed color, yellow y= recessive seed color, green

24. Example of dominant and recessive alleles Dominant – R Recessive – r • The pea you see is round but is made of R and r alleles • This means it shows the dominant ROUND characteristic and carries the recessive wrinkled characteristic without showing it • What other combination of alleles would result in a ROUND pea? • What combination would result in a wrinkled pea?

25. Mendel’s Law of Segregation • A pair of alleles is segregated, or separated, during the formation of gametes (think anaphase II). • Thus, each reproductive cell (gamete) only receives one allele for every trait—either the dominant or recessive allele. • When 2 gametes combine during fertilization, the offspring have 2 alleles controlling a specific trait.

26. Mendel’s Law of Independent Assortment • Alleles for different characteristics are distributed to gametes independently due to the lining up of homologous pairs (think metaphase I). • Thus, the alleles for different characteristics are not connected and are not related to each other. • We show some dominant traits and some recessive traits. • PTC paper demo • Class survey demo

27. Molecular Genetics • Mendel’s findings have had huge implications for modern genetics. • Molecular genetics is the study of the structure and function of chromosomes and genes. • The main ideas of: • Genes • Alleles • Dominance and recessiveness • Making proteins from the genes to exhibit the phenotype • It all gave rise to the huge advancements in genetics today (think HGP and your research)

28. Punnett Squares • Used to show all genotypic combinations of the offspring • Used to find the probability of having offspring with a specific trait (very useful if you want to be a genetic counselor) • Can and should be used on every problem you do to show your work and act as evidence for your answer

29. Patterns of Inheritance Genetics Continued

30. Patterns of Inheritance • Dominant/Recessive • Incomplete Dominance • Codominance • Multiple Alleles • Sex-linked

31. WW = purple Ww = purple ww = white Dominant/Recessive • One allele is dominant over the other (capable of masking the recessive allele)

32. WW Ww Ww ww Problem: Dominant/Recessive • In pea plants, purple flowers (W) are dominant over white flowers (w) show the cross between two heterozygous plants. W w GENOTYPES • WW= 1:4(25%) • Ww = 2:4 (50%) • ww = 1:4 (25%) W w PHENOTYPES - Purple= 3:4 (75%) -White= 1:4 (25%)

33. Symbols used in pedigree charts: Carrier male Carrier female

34. Determine whether the trait is dominant or recessive. • Here are some rules to follow. • For those traits exhibiting dominant gene action: • affected individuals have at least one affected parent • the phenotype generally appears every generation • two unaffected parents only have unaffected offspring • Affected offspring are both male and female

35. The following is the pedigree of a trait controlled by dominant gene action.

36. And for those traits exhibiting recessive gene action: • unaffected parents can have affected offspring • Two affected parents will only have affected offspring • affected progeny are both male and female

37. The following is the pedigree of a trait controlled by recessive gene action.

38. DIHYBRID CROSS = TWO TRAITS

39. P T P t p T p t PpTt x PpTt eggs sperm P T P t p T p t

40. P T P t p T p t P T P t PPTt PPtt PpTt Pptt PpTt ppTt p T PpTT ppTT p t PpTt Pptt ppTt pptt PPTT PPTt PpTt PpTT

41. Purple Tall = 9 = 56% Purple short = 3= 19% white Tall = 3 = 19% white short = 1 = 6% Dihybrid practice

42. RR = red R’R’ = white RR’ = pink Incomplete Dominance • A third (new) phenotype appears in the heterozygous condition. • Could be thought of as a blending of the 2 traits • Flower Color in 4 O’clocks

43. RR = red R’R’ = white Incomplete Dominance • Show a cross between a red flower and a white flower. R’ R’ R R

44. RR’ = pink Results: Incomplete DominanceCross Red Flower with a White Flower Genotype: • RR’= 4:4 (100%) Phenotype: • Pink= 4:4 (100%)

45. R R’ R’ R’ RR’ RR’ R’R’ R’R’ Problem: Incomplete Dominance • Show the cross between a pink and a white flower. GENOTYPES: • RR’= 2:4 (50%) • R’R’= 2:4 (50%) PHENOTYPES: • Pink= 2:4 (50%) • White= 2:4 (50%)

46. SS’ = some of each-Carrier S’S’ = sickle cells- SICK SS = normal cells Codominance • The heterozygous condition, both alleles are expressed equally • Sickle Cell Anemia in Humans sick Can also be written as two different letters – S (normal) and C(sickled) so SS would be healthy, SC would be a carrier and CC would be sick

47. SS’ S’S’ S’S’ SS’ Problem: Codominance • Show the cross between an individual with sickle-cell anemia and another who is a carrier but not sick. S S’ GENOTYPES: • SS’= 2:4 (50%) • S’S’= 2:4 (50%) • - S’ S’ PHENOTYPES: • Carrier= 2:4 (50%) • Sick= 2:4 (50%)

48. So How Are They Different? • How is Incomplete Dominance different from Dominant/Recessive? • How is Codominance different from Dominant/Recessive? • How are Incomplete Dominance and Codominance different from one another? Practice WS and Formative Assessment

49. KARYOTYPE • chart of the chromosomes an individual has. • SEX CHROMOSOMES: X and Y – determine the sex of an organism. • XX = female • XY = male • AUTOSOMES: 22 pairs of chromosomes that do not determine sex.

50. Sex-Linked Traits • SEX-LINKED TRAIT: found on the X or Y chromosome • X-linked : found on the X • Y-linked : found on the Y • AUTOSOMAL TRAIT: exists on any chromosome that does not determine the sex of the organism.