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Mendelian Genetics

Mendelian Genetics. Gregor Mendel. 19th Century Austrian Scientist and friar Worked with pea plants in the monastery garden.

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Mendelian Genetics

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  1. Mendelian Genetics

  2. Gregor Mendel • 19th Century Austrian Scientist and friar • Worked with pea plants in the monastery garden. • Mendel's first law of segregation states that genes do not blend but behave as independent units that pass on to the next generation. After sexual reproduction, offspring end up with one allele from each parent.

  3. Monohybrid crosses

  4. Keywords • F1 generation: First generation of offspring produced from pure-breeding dominant and recessive parents • F2 generation: Second generation produced by crossing the F1 generation. • Pure breeding: Homozygous recessive or dominant individuals • Test cross: An individual is bred with a homozygous recessive to discover its genotype.

  5. Punnett Squares • Draw the F1 generation for Mendels cross of Tall pure breeding plants TT with pure breeding short plants tt.

  6. Punnett Squares • Draw the F2 generation for Mendels Cross of heterozygous plants with each other Tt x Tt

  7. Peas continued • Mendel also studied the surface of peas and discovered they were wrinkled or round. This is another trait controlled by one gene. • The allele creating wrinkled peas does not allow a protein to be made which converts sugar to starch. Thus the extra sugar in the peas increases its osmotic potential and more water moves into the pea. When the pea is dried the extra water is lost and wrinkles....

  8. Other Monohybrid patterns • So far you have only learned about simple dominant recessive patterns but not all alleles work in this way... • 1. Incomplete dominance • Alleles are neither dominant or recessive. A heterozygous phenotype is a blend of the two alleles. Eg: Red RR x White rr flowers makes Pink Rr flowers...a blend of the two colours... • Examples are red and white and pink snap dragons, chestnut and cream horses...make palamino horses.

  9. Tay Sachs Disease • Incomplete dominance example... • Disease prevents body making enzyme which prevents fluid build up in brain. • Death by age 2-3 • Gene is recessive. • Homozygous recessive = death • heterozygous = half normal levels of enzyme produced and normal development occurs

  10. Punnett Squares • Draw a Punnett square for a heterozygous cross with incomplete dominance for Tay Sachs Ss x Ss

  11. 2. Codominance • Both alleles are dominant and are expressed equally • In Punnett squares the gene is represented by a letter and the alleles by super scripts. • Examples are animals and flowers which are mottled or mixed in colour.

  12. 3. Lethal Alleles • Allele combinations which code for a phenotype which causes the death of the individual. • Example: Manx cats have no tails due to a mutant allele M causing abnormal development of tail ones. • All Manx cats are heterozygous Mm. • Mutant gene is dominant. • cats with MM die early in development

  13. Punnett Squares • Draw the F1 generation for breeding 2 heterozygous Manx cats Mm x Mm

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