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Basic Genetics

Basic Genetics. *. View video at: https :// www.youtube.com / watch?v =YxKFdQo10rE. Mendel stated that physical traits are inherited as “particles” Mendel did not know that the “particles” were actually Chromosomes & DNA. Particulate Inheritance. *. Genetic Terminology.

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Basic Genetics

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  1. Basic Genetics *

  2. View video at: https://www.youtube.com/watch?v=YxKFdQo10rE

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

  4. Genetic Terminology • Trait - any characteristic that can be passed from parent to offspring (a genetically determined characteristic or condition) • Heredity - passing of traits from parent to offspring • Genetics - study of heredity *

  5. Types of Genetic Crosses • Monohybrid cross - cross involving a single traite.g. flower color • Dihybrid cross - cross involving two traits e.g. flower color & plant height *

  6. Punnett Square Used to help solve genetics problems *

  7. Genetic Terms • Alleles – forms or versions of a gene • The Gene is for pea color and the alleles are green and yellow • Usually two or more alleles for a particular gene • Dominant – the dominant trait is expressed as long as one dominant allele is present (R) • Recessive – trait is only expressed when there are two copies of the recessive allele (r) *

  8. More Terminology • Genotype - gene combination for a trait, the alleles an individual has(RR, Rr, rr) • Phenotype - the physical expression of the genotype(red, white) *

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

  10. Genotypes can be… • Homozygous - Having the same alleles at a particular gene locus on homologous chromosomes (RR or rr) • Heterozygous –Having different alleles at a particular gene locus on homologous chromosomes     (Rr); also calledhybrid *

  11. MonohybridCrosses *

  12. P1 Monohybrid Cross → F1 • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: RoundseedsxWrinkled seeds • RRx rr Genotype:Rr Phenotype:Round GenotypicRatio:All alike PhenotypicRatio: All alike r r Rr Rr R R Rr Rr *

  13. P1 Monohybrid Cross Review • Homozygous dominant x Homozygous recessive • Offspring (F1 generation)are allHeterozygous(hybrids) • Genotypic & Phenotypic ratio is 1, the genotypes are the same, the phenotypes are the same. *

  14. F1 Monohybrid Cross → F2 • Trait: Seed Shape • Alleles: R – Round r – Wrinkled • Cross: Roundseeds xRound seeds • Rrx Rr Genotype:RR, Rr, rr Phenotype:Round & wrinkled G.Ratio:1:2:1 P.Ratio: 3:1 R r RR Rr R r Rr rr *

  15. F1 Monohybrid Cross Review • Heterozygous x heterozygous • Offspring (F2 generation):25% Homozygous dominantRR50% HeterozygousRr25% Homozygous Recessiverr • Genotypic ratio is1:2:1 • Phenotypic Ratio is 3:1 *

  16. Mendel’s Laws *

  17. 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 rr yields all Rr (round seeds) *

  18. Law of Segregation • During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. • Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring. *

  19. Applying the Law of Segregation *

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

  21. Dihybrid Cross • A breeding experiment that tracks the inheritance of two traits. • Each pair of alleles segregates independently during gamete formation • How to calculate number of gametes: 2n (n = # of heterozygote traits) *

  22. Dihybrid Cross • Traits: Seed shape & Seed color • Alleles:R round r wrinkled Y yellow y green RrYy x RrYy RY Ry rY ry RY Ry rY ry All possible gamete combinations *

  23. Dihybrid Cross RY Ry rY ry RY Ry rY ry *

  24. Dihybrid Cross 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 *

  25. Summary of Mendel’s laws 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 *

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