1 / 67

Genetics

Genetics. Unit 8. Gregor Mendel – The Father of Genetics. Lived from 1822-1884 Austrian monk Studied pea plants Developed the Laws of Inheritance The importance of his work was not recognized until the 20 th century. Site of Gregor Mendel’s Experimental Garden.

kaiyo
Télécharger la présentation

Genetics

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Genetics Unit 8

  2. Gregor Mendel – The Father of Genetics • Lived from 1822-1884 • Austrian monk • Studied pea plants • Developed the Laws of Inheritance • The importance of his work was not recognized until the 20th century

  3. Site of Gregor Mendel’s Experimental Garden

  4. Particulate Inheritance • Mendel knew that something was passed from parent to offspring that affected physical traits  he called them “particles” • He did not know that these particles were actually chromosomes and DNA

  5. Words to Know… • Trait- any characteristic that can be passed from parent to offspring • Heredity- passing of traits from parent to offspring • Genetics- study of heredity • Gene- a sequence of DNA that codes for a protein and thus determines a trait

  6. Punnett Squares • Created by Reginald Punnett (1875-1967) • Used to help solve genetics problems

  7. Punnett Square Rules: • One parent per side of the square • Capital letters always come first: Aa = correct, aA = wrong • Keep the same letters together:AaBB = correct, ABBa = wrong

  8. Types of Crosses • Monohybrid cross - cross involving a single traitExample: seed color • Dihybrid cross - cross involving two traits Example: seed color AND wrinkled/smooth

  9. Words to Know… • Alleles- two forms of a gene(dominant & recessive) • Dominant - stronger of two genes expressed in the hybrid; represented by a capital letter (R) • Recessive – gene that shows up less often in a cross; represented by a lowercase letter (r)

  10. Words to Know… • Genotype - gene combination for a trait(e.g. PP, Pp, pp) • Phenotype - the physical feature resulting from a genotype(e.g. purple, white)

  11. Words to Know… • Homozygousgenotype - gene combination involving 2 dominant or 2 recessive genes (ex. RR or rr);also calledpure-bred • Heterozygousgenotype - gene combination of one dominant & one recessive allele (ex. Rr);also calledhybrid

  12. Mendel’s Experiments • Why use peas? • They can be grown in a small area • They produce many offspring very quickly • They can be self-pollinated to make pure-breds • They can be artificially cross-pollinated to make hybrids

  13. Mendel’s Experiments • Mendel studied the peas over several generations • He observed and recorded 8 traits: • Seed shape--- Round (R) or Wrinkled (r) • Seed Color---- Yellow (Y) or  Green (y) • Pod Shape--- Smooth (S) or wrinkled (s) • Pod Color---  Green (G) or Yellow (g) • Seed Coat Color---Gray (G) or White (g) • Flower position---Axial (A) or Terminal (a) • Plant Height--- Tall (T) or Short (t) • Flower color --- Purple (P) or white (p)

  14. The Results

  15. Words to Know… • Parental P1 Generation= the parental generation in a breeding experiment. • F1 generation= the first-generation offspring in a breeding experiment. (1st filial generation) • From breeding individuals from the P1 generation • F2 generation= the second-generation offspring in a breeding experiment. (2nd filial generation) • From breeding individuals from the F1 generation

  16. Following the Generations Cross 2 Pure PlantsTT x tt Results in all HybridsTt Cross 2 Hybridsget3 Tall & 1 ShortTT, Tt, tt

  17. Monohybrid Crosses

  18. P1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxWrinkled seeds RRxrr Genotype:Rr Phenotype:Round GenotypicRatio:All alike PhenotypicRatio: All alike r r Rr Rr R R Rr Rr

  19. F1 Monohybrid Cross • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: Roundseeds xRound seeds RrxRr Genotype:RR, Rr, rr Phenotype:Round & wrinkled G.Ratio:1:2:1 (25%, 50%, 25%) P.Ratio:3:1 (75%, 25%) R r RR Rr R r Rr rr

  20. …And Now the Test Cross • Mendel then crossed a pure & a hybrid from his F2 generation • This is known as an F2 or test cross • There are two possible testcrosses:Homozygous dominant x HybridHomozygous recessive x Hybrid

  21. F2 Monohybrid Cross (1st) • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxRound seeds RRxRr Genotype:RR, Rr Phenotype:Round GenotypicRatio:1:1 PhenotypicRatio: All alike R r RR Rr R R RR Rr

  22. F2 Monohybrid Cross (2nd) • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: WrinkledseedsxRound seeds rrxRr R r Genotype:Rr, rr Phenotype:Round & Wrinkled G. Ratio:1:1 P.Ratio: 1:1 Rr rr r r Rr rr

  23. bC b__?_ bc Test Cross • A mating between an individual of unknown genotype and a homozygous recessive individual. • Example:bbC_?_ x bbcc • BB = brown eyes • Bb = brown eyes • bb = blue eyes • CC = curly hair • Cc = curly hair • cc = straight hair

  24. bC b___ C bC b___ c bc bbCc bbCc or bc bbCc bbcc Test Cross • Possible results:

  25. Mendel’s Laws

  26. Law of Dominance • Dominant traits mask recessive traits • In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. • All the offspring will be heterozygous and express only the dominant trait. • RR x rryields all Rr (round seeds)

  27. Law of Segregation • Only one allele is passed on from each parent • During the formation ofgametes (eggs or sperm), thetwoalleles responsible for a trait separate from each other. • Alleles for a trait are then "recombined" atfertilization, producing the genotype for the traits of the offspring.

  28. Law of Independent Assortment • Alleles for different traits are inherited independently from one another • Example: You can get your hair color from Mom and your eye color from Dad

  29. How many types of gametes can be produced? • Formula = 2n • n = # of heterozygous alleles • 1. RrYy n=2  4 different gamete types • 2. AaBbCCDd n=3  8 different gamete types • 3. MmNnOoPPQQRrssTtQq n=6  64 different gamete types

  30. Incomplete Dominance and Codominance

  31. Incomplete Dominance • F1 hybrid offspring will have a “blended” appearance between the two phenotypes • Example: Snapdragons (flower) • Red (RR) x white (rr) = Pink (Rr)

  32. Codominance • Two different alleles are completely expressed at once in heterozygous individuals • Example: Calico cat expresses orange AND black genes • Example 2: Human blood type Four types: • 1. type A = IAIA or IAi • 2. type B = IBIB or IBi • 3. type AB = IAIB • 4. type O = ii

  33. Codominance • Question:If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? • boy-type O (ii) X girl-type AB (IAIB)

  34. IA i IAIB IB i ii Codominance • Answer: Parents: genotypes = IAi and IBi phenotypes = A and B

  35. What does this symbol mean? • RR’ • It is just another way of marking a trait • For example: Instead of R = red and r = white, you have R = red and R’ = white • It is usually used with non-Mendelian genetics  What is this?

  36. Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits carried on X chromosome • Therefore, males are the most affected  no “back-up copy”

  37. fruit fly eye color XX chromosome - female Xy chromosome - male Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes

  38. Xr Xr XR Y Sex-linked Trait Problem • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female

  39. Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y Sex-linked Trait Solution: 50% red eyedfemale 50% white eyed male

  40. What is a carrier? • A carrier is an individual who has a recessive trait that they can pass on to their off-spring, but don’t express • They “carry” it to the next generation • For sex-linked traits, women are usually carriers

  41. Human Genetics

  42. How do we study human genetics? • There are some major problems scientists must overcome to study human genetics • It is not ethical to do a test cross on a human being • Humans have long life spans, long gestational period, and a small number of offspring  hard to trace a trait over several generations

  43. How do we study human genetics? • Population sampling = study how often a trait is found in a small, randomly selected group • Problem: It is really hard to get a truly random sample • Pedigree = a graphic record of a trait over several generations within a family; use family/historical records, photographs, medical records, etc. • Only trace ONE trait per pedigree

  44. What do the shapes in a pedigree mean?

  45. Connecting lines indicate relationships in a family • P1 • F1 • F2

  46. Pedigree Example • The parents in the P1 generation MUST have been carriers • Neither of them show the trait, but they had a child who did • Therefore, they CARRIED the trait to the next generation

  47. Genetic Disorder vs Chromosomal Disorder • A genetic disorder is caused by a defect in a single gene • A chromosomal disorder is caused by an entire extra or deleted chromosome

More Related