Mendel and the Gene Idea

1. Mendel and the Gene Idea Chapter 14

2. Gregor Mendel studied pea plants to determine how traits were passed. • Pea plants available in varieties with distinct heritable features (characters) with different variants (traits). • Pea plants normally self-fertilize - Mendel used them to cross-fertilize to study traits.

4. Mendel cross-pollinated (hybridize) 2 contrasting, true-breeding pea varieties. • True-breeding parents - P generation; hybrid offspring - F1 generation. • Mendel would allow F1 hybrids self-pollinate to produce F2 generation.

5. http://www.greendiary.com/images/royal_white_bengal_tiger_cub.jpghttp://www.greendiary.com/images/royal_white_bengal_tiger_cub.jpg

6. Thought genes blended - if purple flower was crossed with white flower result would be light purple flowers. • All flowers were purple.

8. Flowers self-fertilized, Mendel found white flower reappeared in next generation. • Ratio of purple flowers to white flowers in F2 generation was 3:1.

11. Mendel developed hypothesis to explain process - 4 different ideas. • 1Alternative versions of genes (different alleles) account for variations in inherited characters. • 2For each character, organism inherits 2 alleles, one from each parent. • Alleles can be same or different.

13. 3If 2 alleles differ - dominant allele fully expressed in organism’s appearance. • Recessive allele - no noticeable effect on organism’s appearance. • 42 alleles for each character segregate (separate) during gamete production.

14. http://152.16.198.53/GeneticsModules/Design/images/Slide30101.jpghttp://152.16.198.53/GeneticsModules/Design/images/Slide30101.jpg

15. 2 thoughts behind 2 different traits – either transmitted as package, or inherited separate of one another. • Not linked because of inheritance patterns. • Independent assortment of each pair of alleles during gamete formation - Mendel’s law of independent assortment.

16. http://fig.cox.miami.edu/~cmallery/150/mitosis/sf9x5b.jpg

17. Mendel had 3 different laws. • 1Law of dominance and recessiveness - 1 gene dominant over more recessive gene. • 2Law of segregation - alleles separate during meiosis. • 3Law of independent assortment - alleles organize in gametes regardless of other alleles.

18. http://oak.cats.ohiou.edu/~ballardh/pbio475/Heredity/Dominance-relationships.JPGhttp://oak.cats.ohiou.edu/~ballardh/pbio475/Heredity/Dominance-relationships.JPG

19. 2 identical alleles for character - homozygous. • 2 different alleles for character -heterozygous. • Description of organism’s traits - phenotype. • Description of genetic makeup - genotype.

20. http://discover.edventures.com/images/termlib/h/homozygous/support.gifhttp://discover.edventures.com/images/termlib/h/homozygous/support.gif

21. Punnett square predicts results of genetic cross between individuals of known genotype. • Testcross, breeding homozygous recessive with dominant phenotype, but unknown genotype - determines identity of unknown allele.

23. Mendel’s experiments focused on monohybrid crosses - 1 trait at a time. • Dihybrid crosses involving probabilities of 2 different traits.

24. http://fig.cox.miami.edu/~cmallery/150/mendel/sf10x9.jpg

25. Mendel’s ideas based on probability. • Toss coin 4 times - coin has ½ chance of coming up heads every time. • Each toss independent of 1 done before. • Probability coming up heads all 4 times: ½ * ½ * ½ * ½ = 1/8 - rule of multiplication.

26. 12.2

27. Law of addition - determines chances of an event happening in different ways. • 2 ways F1 gametes can combine to form heterozygote. • Dominant allele could come from sperm, recessive from ovum (probability = 1/4) or other way (probability = 1/4). • Probability of heterozygote is 1/4 + 1/4 = 1/2.

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29. * • Incomplete dominance also occurs in offspring - heterozygotes have completely different phenotype than homozygotes - happens in snapdragons. • Homozygous recessive flowers - white; homozygous dominant flowers - red; heterozygotes - pink.

30. http://www.gwu.edu/~darwin/BiSc150/One/rose.GIF

32. Codominance - 2 alleles affect phenotype in separate, distinguishable ways - blood type. • If you inherit A allele and B allele - blood type will be AB; AA or AO - blood type will be A. • A dominant to O, B dominant to O, A codominant to B.

33. Blood type important - type A has anti-B antibodies. • Exposed to B blood - clump together causing transfusion reaction. • Blood type O - both antibodies - can donate to any other blood type. • AB has neither antibodies - can receive from any blood type.

35. Dominant genes – not necessarily more popular in given population. • Most genes do not control 1 trait -pleiotropic, affecting more than 1 phenotypic character. • Epistasis - gene at 1 locus alters phenotypic expression of gene at second locus.

36. http://www.biology.arizona.edu/mendelian_genetics/problem_sets/dihybrid_cross/graphics/13punnet.gifhttp://www.biology.arizona.edu/mendelian_genetics/problem_sets/dihybrid_cross/graphics/13punnet.gif

37. In mice 1 gene determines whether or not there will be coat color. • Gene turned off - mouse will be white; turned on, another locus will determine what color is (brown or black).

38. http://discover.edventures.com/images/termlib/l/locus/support.gifhttp://discover.edventures.com/images/termlib/l/locus/support.gif

39. Quantitative characters vary in population along continuum. • Polygenic inheritance - more than 1 gene controls single trait. • Skin color - controlled by at least 3 different genes - responsible for variety of skin colors.

41. Phenotype depends on environment. • Nutrition influences height, exercise alters build, sun-tanning darkens skin, experience improves performance on intelligence tests.

42. Genetic experiments cannot ethically be performed on humans - geneticists use pedigrees to look at traits found in families. • Family tree created showing absence or presence of specific trait to determine how passed.

44. Ethnicity plays role in genetic disease patterns. • Sickle-cell anemia found predominately in African-Americans - causes red blood cells to be sickle shaped instead of normal disk shape causing cells to get stuck in vessels.

46. Cystic fibrosis affects mostly Caucasians. • Cystic fibrosis - multi-system disease causes mucous to build up in various organs, especially lungs.

47. http://www.humanillnesses.com/original/images/hdc_0001_0001_0_img0072.jpghttp://www.humanillnesses.com/original/images/hdc_0001_0001_0_img0072.jpg

48. Tay-Sachs affects people of Jewish descent. • Tay-Sachs affects brains of small children, ultimately causing death of child prior 5 years old.

49. http://img.search.com/b/b3/300px-Autorecessive_tay_sachs.gif

50. Some genetic diseases, i.e. dwarfism -dominant diseases - child has 50% chance of inheriting disease because 1 parent disease. • Huntington’s disease - dominant disease that affects nervous system. • Most dominant diseases not lethal (Huntington’s disease is).