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Genetics

Genetics. A. The work of Gregor Mendel. 1. Monohybrid crosses. 2. Dominant and recessive alleles. 3. Law of Segregation. B. Mendel and meiosis. Who was this Mendel and what the heck is he doing in a monastery?. born in 1822. trained himself to be a naturalist early in life.

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Genetics

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  1. Genetics A. The work of Gregor Mendel 1. Monohybrid crosses 2. Dominant and recessive alleles 3. Law of Segregation B. Mendel and meiosis

  2. Who was this Mendel and what the heck is he doing in a monastery? • born in 1822 • trained himself to be a naturalist early in life • worked as a substitute science teacher • failed the qualifying exams to be a regular high school teacher! • joined a monastery in Brunn, Austria • sent to Vienna U. to study science and math

  3. MendelWeb Mendel’s first published work: "Versuche über Pflanzen-Hybriden“ or Experiments in Plant Hybridization was a landmark in clarity and insight! Trained as a mathematician and a biologist, he figured out the laws of inheritance… mathematically!!

  4. The work of Gregor Mendel • worked with pea plants… …he called them his children! Why pea plants??? There was a long-standing tradition of breeding pea plants at the monastery where Mendel lived and worked

  5. So…they were readily available and they come in lots of varieties! …there were plants with different flower colors, seed color, flower position etc..

  6. ‘Brother Greg... We grow tired of peas again!!!’

  7. And best of all… Pea plants flowers can reproduce by themselves This allowed Mendel to see if strains were true breeding and to produce hybrids

  8. How Mendel made hybrids… He’d then tie little bags around the flowers to prevent contact with stray pollen.

  9. Mendel’s hybridization experiments… Monohybrid crosses: Parental Generation True-breeding purple flower True-breeding white flower x All purple flowers (the hybrids) F1 generation Allowed F1 offspring to self-fertilize 705 purple F2 generation 224 white

  10. The results of Mendel’s monohybrid crosses led him to propose… • All organisms contain two “units of heredity” for each trait (alleles). • Dominant and recessive alleles… …and organisms can have any combination of the two alleles (2 dominants, 2 recessives or a mixture 1 dominant and 1 recessive). • The Law of Segregation – during gamete formation, alleles separate randomly into separate gametes.

  11. A bit of genetic jargon… phenotype vs. genotype What the organism looks like What alleles the organism has - its genetic makeup

  12. More jargon… homozygous vs. heterozygous P 2 of the same alleles: PP or pp 2 different alleles: Pp p

  13. A Punnett square

  14. A Punnett square… Gametes from one parent p P PP Pp P Gametes from other parent purple purple pp Pp p purple white Ratio: 3:1 or ¾ purple, ¼ white

  15. Let’s relate Mendel’s findings to what we now know about gamete formation True-breeding white flower True-breeding purple flower x all purple P P p p P p P p p p p P P P

  16. purple hybrid x purple hybrid F1 generation P p P p P P p p p p P P p p P P F2 PP (purple) Pp (purple) Pp - purple pp - white

  17. Join to your partner and together, work on the following… Determine the phenotypic and genotypic ratios for each of the following monohybrid crosses. Phenotypic ratio Genotypic ratio Aa x Aa 3:1 (dom:rec) 1:2:1 (hd:h:hr) AA x Aa 1:0 (dom:rec) or all dominant 1:1:0 (hd:h:hr) aa x Aa 1:1 (dom:rec) 0:1:1 (hd:h:hr) AA x aa 1:0 (dom:rec) or all dominant 0:1:0 (hd:h:hr) hd = homozygous dominant; h = heterozygous; hr = homozygous recessive

  18. SO, NOW IT’S YOUR TURN TO WORK ALONE Click on the site below http://www.mendel-museum.com/eng/1online/experiment.htm

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