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Genetics

Genetics. Genetics includes the study of heredity, or how traits are passed from parents to offspring.   The topics of genetics vary and are constantly changing as we learn more about the genome and how we are influenced by our genes. Gregor Mendel.

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Genetics

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  1. Genetics

  2. Genetics includes the study of heredity, or how traits are passed from parents to offspring.   The topics of genetics vary and are constantly changing as we learn more about the genome and how we are influenced by our genes.

  3. Gregor Mendel • Studied the inheritance of traits in pea plants • Developed the laws of inheritance • Mendel's work was not recognized until the turn of the 20th century

  4. Gregor Mendel • In 7 years (1856) Mendel cultivated and tested some 28,000 pea plants • He found that the plants' offspring retained traits of the parents • Called the “Father of Genetics"

  5. Inheritance • Mendel stated that physical traits are inherited as “particles” • Mendel did not know that the “particles” were actually Chromosomes & DNA

  6. Key Terms • Trait - any characteristic that can be passed from parent to offspring • Heredity- passing of traits from parent to offspring • Genetics – the science of heredity

  7. Types of Genetic Crosses • Monohybrid cross - cross between individuals involving one pair of contrasting traits e.g. flower color • Dihybrid cross - cross involving two traits e.g. flower color & plant height

  8. Punnett Square Used to help solve genetics problems

  9. Designer “Genes” • Alleles – alternative form 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. More Key Terms • Genotype -The genes of an individual; combination of genes for one or more specific triats They determine what it will look like… • Phenotype – an organisms appearance (that result from the genotype and environment) 11

  11. Genotype & Phenotype in Flowers Genotype of alleles:R= red flowerr= yellow flower All genes occur in pairs, so 2 alleles affect a characteristic Possible combinations are: GenotypesRRRrrr PhenotypesRED REDYELLOW

  12. Genotypes • Homozygous - gene combination that has identical alleles for a trait (2 dominant or 2 recessive genes) • e.g. RR or rr ; also called pure  • Heterozygous - gene combination that has two different alleles for a trait (one dominant & one recessive allele) •    e.g. Rr; also called hybrid

  13. PRACTICE • Brown eyes are dominant to blue eyes • Bb • BB • bb

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

  15. Monohybrid Crosses

  16. P1 Monohybrid Cross • Trait: Seed Shape • Alleles:R– Roundr– Wrinkled • Cross: Round seeds x Wrinkled seeds • RR x rr Genotype:Rr Phenotype: Round GenotypicRatio:All alike PhenotypicRatio: All alike r r Rr Rr R R Rr Rr

  17. P1 Monohybrid Cross Review • Homozygous dominant x Homozygous recessive • Offspring all Heterozygous (hybrids) • Offspring called F1 generation • Genotypic & Phenotypic ratio is ALL ALIKE

  18. F1 Monohybrid Cross • Trait: Seed Shape • Alleles:R– Roundr– Wrinkled • Cross: Round seeds x Roundseeds • Rr x Rr R r Genotype:RR, Rr, rr Phenotype: Round & wrinkled G.Ratio:1:2:1 P.Ratio: 3:1 RR Rr R r Rr rr

  19. F1 Monohybrid Cross Review • Heterozygous x heterozygous • Offspring:25% Homozygous dominant RR50% Heterozygous Rr25% Homozygous Recessive rr • Offspring called F2 generation • Genotypic ratio is 1:2:1 • Phenotypic Ratio is 3:1

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

  21. F2 Monohybrid Cross (1st) • Trait: Seed Shape • Alleles: R– Roundr – Wrinkled • Cross: Round seeds x Round seeds • RR x Rr 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– Roundr– Wrinkled • Cross: Wrinkled seeds x Roundseeds • rr x Rr R r Genotype:Rr, rr Phenotype: Round & Wrinkled G. Ratio:1:1 P.Ratio:1:1 Rr rr r r Rr rr

  23. F2 Monohybrid Cross Review • Homozygous x heterozygous(hybrid) • Offspring:50% Homozygous RR or rr50% Heterozygous Rr • Phenotypic Ratiois 1:1 • CalledTest Crossbecause the offspring haveSAMEgenotype as parents

  24. Mendel’s Laws

  25. Results of Monohybrid Crosses • Inheritable factors or genes are responsible for all heritable characteristics • Phenotypeis based on Genotype • Each trait is based on two genes, one from the mother and the other from the father • True-breeding individuals are homozygous ( both alleles)are the same

  26. Law of Dominance 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 Dominance

  28. Law of Segregation • During the formation of gametes(eggs or sperm), the two allelesresponsible for a trait separatefrom each other. • Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.

  29. Applying the Law of Segregation

  30. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Mendel’s“Law of Independent Assortment” • a. Each pair of alleles segregates independentlyduring gamete formation • b. Formula: 2n (n = # of heterozygotes)

  31. Law of Independent Assortment • Alleles for differenttraits are distributed to sex cells (& offspring) independently of one another. • This law can be illustrated usingdihybrid crosses.

  32. Question:How many gametes will be produced for the following allele arrangements? • Remember:2n (n = # of heterozygotes) • 1. RrYy • 2. AaBbCCDd • 3. MmNnOoPPQQRrssTtQq

  33. Answer: 1. RrYy: 2n = 22 = 4 gametes RY Ry rY ry 2. AaBbCCDd: 2n = 23 = 8 gametes ABCD ABCd AbCD AbCd aBCD aBCd abCD abCd 3. MmNnOoPPQQRrssTtQq: 2n = 26 = 64 gametes

  34. Dihybrid Cross • Traits: Seed shape & Seed color • Alleles:R round r wrinkled Y yellow y green RrYy x RrYy RY RyrYry RY RyrYry All possible gamete combinations

  35. RY Ry rY ry RY Ry rY ry Dihybrid Cross

  36. RY Ry rY ry Round/Yellow: 9 Round/green: 3 wrinkled/Yellow: 3 wrinkled/green: 1 RY RRYY RRYy RrYY RrYy Ry RRYy RRyy RrYy Rryy rY RrYY RrYy rrYY rrYy ry RrYy Rryy rrYy rryy 9:3:3:1 phenotypic ratio Dihybrid Cross

  37. Dihybrid Cross Round/Yellow: 9Round/green: 3wrinkled/Yellow: 3wrinkled/green: 1 9:3:3:1

  38. 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

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

  40. LAW PARENT CROSS OFFSPRING DOMINANCE TT x tttall x short 100% Tt tall SEGREGATION Tt x Tttall x tall 75% tall 25% short INDEPENDENT ASSORTMENT RrGg x RrGground & green x round & green 9/16 round seeds & green pods 3/16 round seeds & yellow pods 3/16 wrinkled seeds & green pods 1/16 wrinkled seeds & yellow pods Summary of Mendel’s laws

  41. r r Incomplete Dominance • An individual displays a trait that is intermediate between the two parents. • Example: When a snapdragon with red flowers is crossed with a snapdragon with white flowers, a snapdragon with pink flowers is produced. • Neither allele is dominant over the other allele.

  42. Incomplete Dominance

  43. Codominance • Two alleles are expressed (multiple alleles) in heterozygous individuals. • Example: blood type • 1. type A = IAIA or IAi • 2. type B = IBIB or IBi • 3. type AB = IAIB • 4. type O = ii

  44. IA i IAIB IBi IB 1/2 = IAIB 1/2 = IBi IB IAIB IBi Codominance Problem • Example: homozygous male Type B (IBIB) • x heterozygous female Type A (IAi)

  45. IA IB IAi IBi i 1/2 = IAi 1/2 = IBi i IAi IBi Another Codominance Problem • Example:male Type O (ii) x female type AB (IAIB)

  46. 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)

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

  48. Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y • XXgenotype for females • XYgenotype for males • Many sex-linked traits carried on Xchromosome

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

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