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Mendel Genetics Chapter 14

Mendel Genetics Chapter 14. Genetics. The study of heredity. Heredity. Transmission of traits One generation to another Inherited features are the building blocks of evolution. Historically. Blending of parental contributions Example: Tall parent + short parent Medium child.

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Mendel Genetics Chapter 14

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  1. Mendel GeneticsChapter 14

  2. Genetics • The study of heredity

  3. Heredity • Transmission of traits • One generation to another • Inherited features are the building blocks of evolution

  4. Historically • Blending of parental contributions • Example: • Tall parent + short parent • Medium child

  5. Problem • No outside genes • All parents traits blended • Over time all members of the species will look the same.

  6. Variation • Differences in offspring

  7. Vocabulary • Character: • Inheritable feature • Ex: color • Trait: • Alternate forms of the character • Purple or white

  8. Vocabulary • True-breeding: • Produced same variety as the parent • P generation • Parental generation

  9. Vocabulary • First filial generation (F1) • Offspring from the first cross • Second filial generation (F2) • Offspring from the second cross

  10. Vocabulary • Alleles: • Alternate versions of the gene • Dominant: • Trait that is expressed • Recessive: • Trait that is not expressed or hidden

  11. Vocabulary • Homozygous: • Pair of the same alleles • Heterozygous: • Pair of different alleles • Genotype: • Genetic make-up • Phenotype: • Appearance of organism

  12. Vocabulary • Hybridization: • Crossing of parents that are not alike • Hybrids: • Offspring with two alleles for trait • Testcross: • Cross with a homozygous recessive individual • Determines genotype of an individual.

  13. Vocabulary • Self-fertilization: • Fertilization can take place in plant if undisturbed. • Cross-fertilization: • Remove the male parts • Introduce pollen from another strain • Different traits

  14. Vocabulary • Punnett square: • Diagram • Displays allele possibilities of fertilizations

  15. Vocabulary • Monohybrid: • Individuals are heterozygous for one trait • Aa • Tt • Dihybrid: • Individuals are heterozygous for two traits • AaTt

  16. Gregor Mendel • Austrian monk • Studied math & science • University of Vienna • Studied pea plants at the monastery

  17. Why the pea?? • 1. Has been studied • Able to produce hybrid peas • 2. Variety with 7 simple & easy to see traits • Purple vs white flower • 3. Small, easy to grow • Short generation time

  18. 4. Male & female sex organs located on same plant

  19. Mendel • Chose comparable traits • 1. Flower color (white vs purple) • 2. Seed color (yellow vs green) • 3. Shape of seed (smooth vs wrinkled) • 4. Pod color (green vs yellow) • 5. Pod shape (inflated vs constricted) • 6. Flower location (axial vs terminal) • 7. Plant size (tall vs. short)

  20. Mendel’s experiments • Allowed the peas to self-fertilize • Used true-breeding or pure-breeding plants

  21. Mendel’s experiment • Crossed plants with alternate forms of characteristics • Example: • Tall plants with short plants

  22. Mendel’s experiment • Parental generation • Pure white flowered plants X pure purple flowered plants • F1 always revealed purple flowered plants • Crossed the hybrid offspring • F2 filial generation • Some were purple • Some were white

  23. Mendel’s experiment • F1 trait was hidden • F2 trait reappeared • Ratio in the F2 generation • 3:1 dominant:recessive • 3:1 purple:white • All traits revealed this ratio

  24. Mendel’s experiments • F2 generation self-fertilized • White flowers always produce white flowers • Purple flowers • 1/3 produced only purple flowers • 2/3 produced dominant & recessive flowers in a 3:1 ratio

  25. Mendel’s experiment • Concluded that the F2 generation was really 1:2:1 • ¼ pure-breeding dominant individuals • ½ non-pure breeding • ¼ pure-breeding recessive individuals

  26. Mendel’s model • 1. Plants did not produce intermediate offspring. • 2. Alternate trait was there only not expressed

  27. Mendel’s model • 3. Alternate traits segregated in the offspring • 4. Mendelian ratio: • 3:1 in the F2 generation • ¾ dominant • ¼ recessive

  28. Mendel’s model • Alleles remain discrete • Do not influence the other • Do not blend • Are passed on in the gametes

  29. Mendel’s first law of heredity • Law of Segregation: • Alternate alleles of a character • Segregate (separate) from each other & remain distinct. • Seen in meiosis when the homologous chromosomes separate • Form gametes

  30. Mendel’s experiment • Crossed dihybrids • F1 generation demonstrated dominant phenotype for both traits • F2 generation showed a 9:3:3:1 phenotype (16 gamete combinations) • Each trait showed a 3:1 ratio similar to a monohybrid cross

  31. Mendel’s second law of heredity • Law of Independent Assortment: • Genes located on different chromosomes • Assort independently • Assuming the genes are on separate chromosomes

  32. Mendel • Phenotypes may be influenced by many factors • Many different genes • Environment

  33. Incomplete dominance • Not all chromosomes are dominant or recessive • Heterozygous genotype can cause an intermediate between the parents

  34. Codominance • Effect of both alleles can be seen • MN blood groups • Molecules on surface of RBC • MM, NN or MN • MN see affects of both

  35. Codominance • Tay-Sachs disease (homozygous recessive) • Brain cells unable to break down lipids • Lacking enzyme build up lipids • Retardation & early death • Heterozygous • 50% the normal enzyme levels • Survive

  36. Tay Sachs • 1 in 300,000 births in the US • 1 in 3500 births in Ashkenazi Jews • 1 in 28 are carriers in this population

  37. Multiple alleles • ABO blood type • Gene codes an enzyme • Adds a sugar to lipids • Located on the surface of the RBC • Sugars act as recognition markers for the immune system

  38. ABO • 3 gene alleles • 4 different blood types • I is the enzyme • IA (allele) adds galactose • IB (allele) adds galactosamine • i (allele) has no sugar

  39. ABO • Type A IAIA Homozygous • Type A IAi Heterozygous • Type B IBIB Homozygous • Type B IBi Heterozygous • Type AB IAIB Heterozygous • Type O ii Homozygous

  40. Rh blood group • Cell surface marker on the RBC • 85% have the marker • Rh + • Rh - does not have the marker • If a Rh- person gets blood that is Rh + • Develops antibodies against Rh+ blood.

  41. ABO • Problem • Rh- mother gives birth to a child that is Rh + (Rh+ dad) • She has built up antibodies • They could cross into the babies blood. • Erythroblastosis fetalis: • Babies blood clumps due to antibodies against it’s Rh factor • RhoGam

  42. Pleiotropic • Allele has more than one effect on the phenotype • One gene has many effects • Peas: gene for flower color • Codes for seed cover color • Yellow mice • Gene for yellow fur • Same for lethal developmental defect • So homozygous dominant would die

  43. Pleiotropic • Inherited diseases that one gene produces many symptoms • Sickle cell anemia • Anemia • Joint pain/swelling • Heart failure • Splenomegaly • Renal failure

  44. Sickle cell • Single aa change in beta-globin of hemoglobin • Causes hemoglobin to be sticky • Sickle cell shape • Higher incidence to people of African decent 1/500 • Heterozygous for the disease • Have greater resistance to malaria

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