Genetics

1. Genetics

2. Gregor Mendel-Father of Genetics • Born-1822 in Austria • Entered the monastery at age 21. After failing the exam to be a teacher he went to study at the University of Vienna. There he studied with some important scientists of his day.

3. 1857-Mendel began breeding peas in the abbey gardens. • Why was choosing peas so important? • Traits show as “either/or” • Had control over mating (they normally self-fertilize) • He began with true breeding plants

5. P = parent generation • F1 = first generation (first filial) • F2 = second generation (second filial) • Sample cross: • P purple x white flowers • F1 all purple flowers • F2 ¾ purple, ¼ white • Mendel reasoned the white trait was not gone in the F1 but was being masked by the more dominant purple trait

6. Mendel’s law of segregation: • The 2 alleles separate during gamete formation • Each parent has 2 copies of every gene. When forming the sex cells only one copy goes into each cell. If Mom has DD--------eggs all have D If Dad has dd----------sperm all have d

7. A test for the law of segregation: • Purple x white P: PP x pp F1: Pp x Pp F2: 1PP: 2Pp: 1pp *The fact that the white appears again proves that the alleles have to separate from each other.

8. Vocabulary: • Trait-varieties of alleles (purple or white) • Homozygous-alleles are the same, (may be either dominant or recessive-PP, pp, TT, tt) • Heterozygous-alleles are different—Pp, Tt

9. Phenotype-appearance, traits that are visible • Genotype-actual genes present

10. Test cross: • Done to determine if genes are homozygous or heterozygous dominant. • A dominant parent can be either PP or Pp • Cross with a plant of known genes (pp) • If all offspring are purple then parent was PP • If some offspring are white and some are purple then parent was Pp

12. Mendel’s Law of Independent Assortment • From single trait crosses Mendel knew yellow seed were dominant over green seeds and round were dominant over wrinkled. What would happen to theses genes when crossed together? • If Y and R stay together then the ratio in offspring would be 3:1 • Actual ratio is 9:3:3:1. This means that the 2 genes travel independently of each other to gametes

13. Probability and genetics • Probability-the chance an event will occur • An event certain to occur has a probability of 1 • An event certain not to occur has a probability of 0 • Probabilities of all outcomes must add up to 1

14. Rule of multiplication: • Use when each occurrence is a separate event • Example: what is the chance of getting heads on 2 coins tossed simultaneously? • The two coins are separate events. probability of heads on 1st coin = ½ probability of heads on 2nd coin = ½ probability of heads on both is ½ x ½ = ¼

15. What is the chance of getting white flowers? • Chance of egg having p allele is ½ • Chance of sperm having p allele is ½ • ½ x ½ = ¼

16. Rule of addition: • Probability an event can occur in 2 or more ways is the sum of each one separate probability. • Example: what is the probability an F2 plant will be heterozygous from a monohybrid cross? • Two out of 4 are heterozygous ¼ + ¼ = ½ P p PP Pp P Pp pp p

17. Monohybrid and dihybrid crosses • Monohybrid – one trait is crossed at a time Punnett square-device for predicting results of a cross recessive trait is written with a small letter dominant trait is written with a capital letter

18. Examples: Trait = seed shape Genes: round = R, wrinkled = r R R R r R R R R r r r r G= P= G= P= G= P=

19. Dihybrid –two traits crossed together • First determine the possible combinations of genes: • YyRr = YR, Yr, yR, yr • Yyrr = Yr, Yr, yr, yr

20. G = P = Yr Yr yr yr YyRr YR YYRr YYRr YyRr YYrr YYrr Yyrr Yyrr Yr YyRr YyRr yyRr yyRr yR Yyrr yyrr yyrr yr Yyrr

21. Inheritance patterns: 1. Incomplete dominance-the appearance of the F1 is a blend of the parents • Example-snapdragons • P red x white • F1 all pink • F2 ¼ red: ½ pink: ¼ white

23. Example: sickle cell anemia • Mutated gene for hemoglobin • Normal genes: HbA HbA • Sickle cell trait: HbA HbS • Sickle cell disease: HbS HbS A person with sickle cell trait produces both normal and sickle cells, a person with the disease makes only sickle cells. They rupture easily, clog arteries, cells don’t get oxygen delivered.

24. 2. Pleiotropy-the expression of one gene can effect many organs or systems (pleio is Greek for more) • Sickle cell • Marfan syndrome-tall body, long arms, nearsighted, weak aorta wall (President Lincoln?) • Cystic fibrosis

25. 3. Co-dominance-both phenotypes are expressed at the same time Example one –the four human blood types are a result of 3 genes IAIBi • A and B are both dominant genes • A = IAIA or IAi • B = IBIB or IBi • O = ii • AB = IAIB Example two-roan cows -- red and white are equal

26. 4. Multiple alleles-three or more alleles of a gene in a population • Example-blood type (3 genes determine 4 blood types) • Example-rabbit fur color • Agouti-gray and yellow (A) • Chinchilla-black and white (a-ch) • Himalayan-white with black extremities (a-h) • Albino-white (a)

27. 5. Polygenic inheritance-many genes contribute to the trait, creates an additive effect • Example: human skin color AABBCCDD is darkest, aabbccdd is lightest. • Other examples are height, weight, eye color

29. 6. Epistasis-one gene alters or interferes with the expression of another. • Example-fur color in many mammals. In mice black hair is dominant to brown. black – B brown – b A second gene determines how much color is deposited in the hair. C—mouse will be black or brown c—mouse will be white *even if the mouse has BB for black hair, if the other genes are cc for no color, the mouse will not show the black fur trait.

30. Environmental effects • -some alleles are temperature sensitive. Examples: arctic foxes, Himalayan rabbits, Siamese cats

31. Some alleles are pH sensitive Example: hydrangeas

32. Locating genes on chromosomes: • The first evidence that showed certain genes were located on a specific chromosome came from Thomas Morgan. • He chose fruit flies to work with • Using eye color as the trait • Females had red eyes (wild) • Males had white (mutant)

33. In his crosses he found that the white eye color was linked to the sex of the fly. • He determined that this meant the gene was on the sex chromosome.

34. Sex linked traits • Remember that humans have 23 pairs of chromosomes. Of those, 22 pairs are autosomes and 1 pair are sex chromosomes. • Male sex chromosomes = XY • Female sex chromosomes = XX • Gender of the offspring is determined by the male and is a 50/50 chance

35. female (XX) male (XY) X X eggs sperm x X Y x Y X X X XX XX XY XY

36. Sex Determination in other animals • Not all animals determine gender like humans. • Grasshoppers have only 1 sex chromosome • Females are XX, males are X • Birds and some fish the female determines the sex of offspring • Females are ZW, males are ZZ • Bees and ants don’t have sex chromosomes • Females come from fertilized eggs (they are 2n) • Males come from unfertilized eggs (they are n)

37. Dosage compensation • Probably occurs to make females and males equivalent in X’s, one X chromosome in a female becomes inactive

38. Inactive X condenses into a compact unit and is pushed to the side. It is called a Barr body. Which X becomes Barr body is random. Females end up as a mosaic—some cells have active X from mom and others have active X from dad. • Examples • Calico cat • Female sweat glands

39. Examples of sex linked traits • X linked recessive-show up in males more often • Hemophilia-blood clotting disorder, ran through royal families in Europe • Dushenne Muscular Dystrophy-muscles atrophy, are replaced by fat tissue during ages of 2 and 10. Typically die in early 20’s

40. Red green color blindness-can’t distinguish between those two colors

42. X linked dominant-rare, few examples • Faulty enamel trait-the hard enamel on teeth fails to develop correctly

43. Y linked dominant-few traits are on the Y other than male traits. It is questionable if these traits exist

44. Chromosome abnormalities • Chromosome abnormalities may be caused by a change in number or a change in the structure of the chromosome.

45. Changes in chromosome number: • Nondisjunction-homologous chromosomes do not separate correctly during meiosis. One gamete receives an extra copy, other receives none. This creates: • Polyploidy-entire sets of chromosomes may be added • Aneuploidy-whole chromosomes are lost or gained

47. Nondisjunction in sex chromosomes • 45 XO – Turner’s syndrome • 1 in 5000 female births • Short stature, barrel chest, thick neck with webbing, normal intelligence but may have learning disabilities, often has heart problems, no Barr bodies, sterile

48. 47 XXX – triple X • Sex- female • Usually fertile, fairly normal • One X will remain functional and the other two become Barr bodies • 47 XXY – Klinefelter’s • Sex- male • Unusually tall, extra X becomes Barr body, usually sterile, may show breast development

49. 45 OY - never develops • 47 XYY – Supermale (Jacob’s syndrome) • Unusually tall, severe acne, not well coordinated, emotionally unstable.

50. Nondisjunction in autosomes • Humans who have lost a copy of an autosome do not survive. • Most who inherit an extra copy also do not survive except for 5 of the smaller chromosomes: 13, 15, 18, 21, 22