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Basic principles of genetics

Genetics from the beginning!. Basic principles of genetics. University of Utah Review of Genes etc!. Genetics. Inheritance of traits coded for by genes. The study of Heredity. All the genes in a given population. What is a gene pool?. Evidence for Heredity. Similar phenotype

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Basic principles of genetics

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  1. Genetics from the beginning! Basic principles of genetics University of Utah Review of Genes etc!

  2. Genetics Inheritance of traits coded for by genes The study of Heredity

  3. All the genes in a given population What is a gene pool?

  4. Evidence for Heredity Similar phenotype caused by similarities in genotype

  5. Gregor Mendel Austrian Monk!

  6. Mendel’s Pea Plants Showed Traits that were Markedly Contrasting Could tell tall from short easily

  7. Traits studied by Mendel Markedly contrasting

  8. Male part with pollen Female part with egg

  9. Cross Pollination/Cross Fertilization Pollen from anther transferred to stigma of female part

  10. Gregor Mendel • Cross pollinated pea plants • Studied traits whose expression were markedly contrasting • eg Height: tall vs. short…..no in between • Pure Tall X Pure Short…….cross 1 • All offspring Tall

  11. He then crossed offspring from cross 1 • Offspring: 75% Tall : 25% Short • He reasoned that…… • Gene for tall is dominant • Gene for short is recessive

  12. Summary of Mendel’s Cross • TT x tt --------Tt • Tt x Tt -------- 3 Tall : 1 Short • Parents referred to as P1 • First generation referred to as F1(F=Filial) • Second generation referred to as F2

  13. Monohybrid Cross: Involving 1 trait Punnett Square T T Tt t Tt t Tt Tt Genotypes All Tt Heterozygous Phenotypes All Tall

  14. Monohybrid Cross t T TT T Tt t Tt tt Genotypes 1 TT : 2 Tt : 1 tt Phenotypes 3Tall: 1Short

  15. Genotypes of parents F1 F2 Punnett Square

  16. Crossing Tall and Short Plants Which characteristic appears to be recessive?

  17. Genetics Terminology • Physical appearance = phenotype • Genetic make up causing pheno = genotype • Genotype described using minimum of 2 letters • All traits controlled by at least 2 genes • These referred to as alleles of a pair • For height: alleles are T and t

  18. If genotype is TT, plant is tall (homozygous dominant) • If genotype is Tt, plant is also tall but also a carrier for short (heterozygous) Hybrid & Heterozygous often confused No need to say Heterozygous dominant…why??

  19. More terminology…Yikes!!. • If genotype is tt, plant is short (homozygous recessive or just recessive) • Phenotypic ratio in cross 1 = all tall • Phenotypic ratio in cross 2 = 3 tall : 1 short • Genotypic ratio in cross 2 = 1 TT: 2 Tt: 1 tt • G.R. & P.R. found easily using punnett square

  20. Identify the recessive allele & phenotype Using the following punnett square

  21. Monohybrid Cross t t Tt Tt T t tt tt Genotypes 1 Tt : 1 tt Phenotypes 1 Tall: 1 Short

  22. Conclusions from Mendel’s work • Inherited characteristics controlled by factors (genes) found in gametes • All traits controlled by 2 alleles (minimum). • Some alleles mask effect of others. • These are called dominant alleles

  23. Law of Segregation: Pairs of genes segregate when homologous chromosomes move to opposite poles during meiosis • Law of Independent Assortment: Different pairs of alleles segregate independently of each other

  24. Mendel’s law of segregation

  25. Independent Assortment

  26. Test Cross • Used to determine genotype of individual expressing dominant characteristic • eg. If pea plant is tall • Genotype could be TT or Tt • Only one way to find out! • Cross with homozygous recessive

  27. Test Cross t t No short offspring Tt Tt T T Tt Tt Phenotypes All Tall Genotypes All Tt

  28. Test Cross t t Short offspring Tt Tt T t tt tt Phenotypes 2 Tall : 2 short Genotypes 2 Tt : 2 tt

  29. Summary of Test Cross Results • If some recessive individuals show up….. • Genotype of unknown must be heterozygous • If no recessives show up…. • Genotype is probablyhomozygous dominant

  30. Testcross with monohybrids

  31. Test Crossing Sheep • Sheep ranchers like producing white wool • Easier to dye and less brittle than black • White is dominant, black recessive • If farmer suspects white sheep in herd are heterozygous…what can she/he do????

  32. Farmer may find out for certain by crossing suspected carriers with homozygous recessive (ww) • If some black sheep show up as offspring… • Sheep was a carrier for black wool! (heterozygous) • These sheep make better meat!!!!

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