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Ch 14 Gregor Mendel and Inheritance Study

Ch 14 Gregor Mendel and Inheritance Study. Began research late 1850’s St. Thomas (Augustinian) monastery, Brno, Yugoslavia. 1. “blending” hypothesis genetic material from the two parents blends together (like blue and yellow paint blend to make green).

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Ch 14 Gregor Mendel and Inheritance Study

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  1. Ch 14 Gregor Mendel and Inheritance Study Began research late 1850’s St. Thomas (Augustinian) monastery, Brno, Yugoslavia

  2. 1. “blending” hypothesis • genetic material from the two parents blends together (like blue and yellow paint blend to make green) • What genetic principles account for the passing of traits from parents to offspring? • 2. “particulate” hypothesis • parents pass on discrete heritable units (genes) • Mendel’s pea breeding data • supported the particulate mechanism

  3. Scientific approach Asked question: how are traits inherited? Used convenient model system: garden peas -controlled breeding -a variety of either/or visible traits -quantitative data Derived conclusions based on the data

  4. For example To examine inheritance of flower color Cross-fertilized (hybridized): true breeding purple x true breeding white Measurable character: phenotype

  5. Removed stamens from purple flower Materials & Methods Transferred sperm- bearing pollen from stamens of white flower to egg- bearing carpel of purple flower LE 14-2 Parental generation (P) Stamens Carpel Pollinated carpel matured into pod Planted seeds from pod 100% purple phenotype Examined offspring: all purple flowers First generation offspring (F1)

  6. “True-breeding” plants that produce offspring of the same variety when they self-pollinate

  7. Nomenclature • True-breeding parents • P (generation) • Hybrid offspring (cross between 2 different true-breeding parents) • F1 (generation) • Progeny of F1 self-pollination • F2 (generation)

  8. Results from two crosses P Generation LE 14-3 (true-breeding parents) P1 x P2 Purple flowers White flowers F1 Generation F1 x F1 (hybrids) All plants had purple flowers F2 F2 Generation

  9. Conclusions • Only purple flowers in the F1 hybrids • Purple: dominant trait • White: recessive trait • Same pattern of dominant inheritance - six other pea plant phenotypes, each represented by two traits Mendel’s “heritable factors” (= genes) (though he did not know the existence of DNA)

  10. Mendel’s Model • Inheritance patterns obeyed rules of probability • Assumes each trait has two variants Current knowledge: phenotype is controlled by genes (genotype) paternal and maternal alleles (genes)=two variants positioned at chromosomal locus

  11. LE 14-4 Allele for purple flowers Homologous pair of chromosomes Locus for flower-color gene Allele for white flowers

  12. 3. One of the alleles determines phenotype 2. Offspring inherit two alleles, one from each parent P= purple (dominant allele) p= white (recessive allele) Homozygous if PP or pp (noun; homozygote) PP=_____________________________ pp=___________________________ Heterozygous if Pp (noun: heterozygote)

  13. 4. Law of segregation two alleles for any given phenotype separate during gamete formation. Thus, offspring inherit one allele from each parent. When do alleles first separate from each other? During anaphase I

  14. Convenient quantitative way to predict outcome of crosses Punnett Square Name alleles with single letter Write down genotype of each parent Fill in boxes with all possible combinations of alleles according to parental genotypes On Board

  15. What is the frequency of genotypes of the offspring of the parental cross? 100% heterozygous What is the frequency of phenotypes of the offspring of a parental cross? 100% purple What is the frequency of genotypes of the F1 cross progeny? 50% heterozygous; 25% dominant and recessive homozygous What is the frequency of phenotypes of the F1 cross progeny? 75% purple, 25% white (3:1)

  16. P Generation Purple flowers PP White flowers pp Appearance: LE 14-5_2 Genetic makeup: p P Gametes F1 Generation Appearance: Genetic makeup: Purple flowers Pp Gametes: 1 1 p P 2 2 F1 sperm P p F2 Generation P PP Pp F1 eggs p Pp pp 3 : 1

  17. Genotype Phenotype PP (homozygous Purple 1 LE 14-6 Pp (heterozygous 3 Purple 2 Pp (heterozygous Purple pp (homozygous White 1 1 Ratio 1:2:1 Ratio 3:1

  18. Genotype possibilities (purple flower color)? • How can we determine the genotype of an individual with a dominant phenotype? PP or Pp Test cross Hybridize to individual with homozygous recessive individual (pp) Do Punnett for each. Outcome?

  19. LE 14-7 Dominant phenotype, unknown genotype: PP or Pp? Recessive phenotype, known genotype: pp If Pp, then 1 2 offspring purple and 1 2 offspring white: If PP, then all offspring purple: p p p p P P Pp Pp Pp Pp P P pp pp Pp Pp

  20. Monohybrid vs dihybrid Heterozygous for 1 character Heterozygous for 2 characters Set up a cross between heterozygous purple flowered pea plants Pp x Pp Do a Punnett Square: determine genotypic and phenotypic ratios.

  21. What are patterns of inheritance 2 characters? Given: true breeding P for pea color & shape Dominant characters Yellow Round Recessive characters green wrinkled Set up Parental Cross Set up F1 cross What is phenotypic frequency of the offspring?

  22. P Generation YYRR yyrr Gametes yr YR LE 14-8 YyRr F1 Generation Hypothesis of dependent assortment Hypothesis of independent assortment Sperm YR Yr yR yr 1 1 1 1 4 4 4 4 Sperm Eggs YR yr 1 1 2 2 YR 1 4 Eggs YYRR YYRr YyRR YyRr YR 1 2 F2 Generation (predicted offspring) YYRR YyRr Yr 1 4 YYRr YYrr YyRr Yyrr yr 1 2 YyRr yyrr yR 1 4 YyRR YyRr yyRR yyRr 3 1 4 4 yr 1 4 Phenotypic ratio 3:1 YyRr Yyrr yyRr yyrr 9 3 3 3 16 16 16 16 Phenotypic ratio 9:3:3:1

  23. Observation of a dihybrid cross - Each pair of alleles segregates independently of other pairs of alleles during gamete formation - Mendel proposed the law of independent assortment (Fast forward) Established at metaphase I & II • Note: • Applies only to genes on different, nonhomologous chromosomes • Genes located near each other on same chromosome tend to be inherited together: linkage

  24. Autosomes (22 pr) Sex chromosomes

  25. Inheritance of Sex-Linked Genes Sex chromosomes Carry genes that determine sexual phenotype & other traits Sex-linked genes: Any gene on sex chromosome (usually refers to X-chromosome because of bigger size, more genes)

  26. How to show inheritance of sex-linked traits: follow X and Y chromosomes in a cross LE 15-10 Sperm Sperm Sperm Ova Ova Ova

  27. Sex-linked recessive disorders • Color blindness • Duchenne muscular dystrophy • Hemophilia Present hemophilia problem Mother carrier/ father normal

  28. We’re celebripeas! Questions?

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