Genetics

1. Genetics Lab 11

2. The Family

3. The Principles of Mendel • Experiments in Plant Hybridization” – scientific paper written in 1866 by Gregor Mendel • Went unnoticed until closer to 1900 – • Mendel’s findings: Foundation of Mendelian Genetics • Main idea: dismiss blending theory with Particulate theory

4. Particulate Theory • States: • Inherited characters are determined by particular factors (now called genes) • These factors occur in pairs(genes occur on maternal & paternal homologous chromosomes) • When gametes form, these genes segregate so that only one of the homologous pair is contained in a particular gamete. (remember meosis?)

5. This theory …. • Is known as “ The Law of Segregation” (first law) • His second law: “The Law of Independent Assortment” states: that genes on nonhomologous or different chromosomes will be distributed randomly into gametes.

6. Vocabulary • Gene – a unit of heredity on a chromosome • Alleles – alternate states of genes; contributed to an organism from its parent. Alleles for a particular gene occur in pairs. • Dominant – alleles that mask expression of other alleles; capital letter • Recessive – alleles whose expression is masked; lower case letter

7. Genotype & Phenotype • Genotype: All the alleles of an organism present in a cell (dominant or recessive) • Phenotype: The physical appearance of a trait.

8. Homozygous • When paired alleles are identical: • PP, pp, GG, gg, II, ii

9. Heterozygous • Pairs of different alleles: Pp, Ii, Bb

10. Simple Dominance

11. Generations • Parental generation “P” • First generation: Filial 1: F1 • Next generation: Filial 2: F2 • And so on

12. F1 OffspringPP- homozygous dominant = purplePp – heterozygous - purplepp – homozygous recessive = white • Example: page 191: • Parents: PP and pp • Gametes: P from purple-flowered parent • p from the white-flowered parent • Offspring: genotype: Pp • Phenotype: purple

13. What is the ratio of purple-flowered (PP or Pp) to white flowered (pp) offspring?

14. Answer • Genotypic ratio of F1 generation: • 1 PP : 2 Pp : 1 pp • Phenotypic ratio of F1 generation: • 3 purple : 1 white

15. Procedure 17.2 • Albinos – homozygous recessive (aa) • Suppose a woman having normal colored skin and an albino mother marries an albino man:

16. Normal mom & Albino dad • Genotype of children’s mother: _________________ • Genotype of children’s father: _________________ • Possible gametes of mother: _________________ • Possible gametes of father: _________________ • Genotype ratio of children: _________________ • Phenotype ratio of children: __________________

17. Answer: • 50 % chance of albino kid • 50% chance of normal kid

18. Procedure 17.2 • Color ratio for corn plants • Will not do height  corn did not cooperate • Colors will be purple and yellowy-white ( not red and white) • P- dominant p – recessive • PP – purple • Pp-purple • Pp – yellowy white

19. Corn Parents: PP and Pp • F1 = all Pp • F2 = ? • Pp x Pp • 3 purple : 1 white • 3: 1 phenotypic ratio

20. Activity • Work in your groups: 1 reader, 3 recorders • Read down the corn and give “tic” marks for every purple and “tic” mark in separate column for yellowy-white kernels. • Do for about 200 kernels • See if ratio is as it should be  • Ex: 160/40 = 4 40/40 = 1

21. Incomplete Dominance • In this type of inheritance, the heterozygous genotype results in an “intermediate” characteristic • Ex: Red flower – RR crossed with white flower –rr • Parents: RR (red) x white (rr) • Gametes: R r • Offspring: Rr = pink

22. Lethal Inheritance • Involves the inheriting of a gene that kills the offspring. • Ex: Huntington’s Disease – slow manifestation so offspring generally reproduce before they know they have it. • We will discuss more shortly

23. Other Sources of Genetic Diversity • Multiple alleles • Gene interaction (epistasis) • Continuous variation • Environmental effects • Linkage • Sex linkage

24. Sex-linkage • Color-blindedness (color deficiency) • Inability or decreased ability to see color, or perceive color differences under normal lighting conditions. • The genes that produce photopigments are carried on the X chromosome • If some of these genes are missing or damaged: color blindness will be expressed in males with a higher probability than females because males only have on x chromosome.

25. Remember: Autosomes Sex determining chromosomes (XX, XY) X = about 1500 genes Y = gene poor: 78 genes Colorblindness: recessive mutation on x chromosomes Hemophilia: mutations on x chromosome

26. Hemophilia hemophilia - recessive X chromosome mutations • So both x chromosomes have to have a hemophilia mutation to have hemophilia (phenotype) • XX^h = mom a carrier ; no hemophilia • X^hX^h – mom Does have hemophilia • For man to have this phenotype – only needs on one x chromosome he has : X^hY – has hemophilia • Who more likely to have? Male or female? • Female needs 2 (1/7000 x 1/7000 = 1/49,000,000), men need on one (1 in 7000)

27. Other Human Traits • Page 197

28. Analyzing Pedigrees page 199 - 200 • Researchers cannot control crosses in humans as they do in plants like Mendel did. • Geneticists study crosses that have been performed already • Family histories

29. Pedigrees • A consistent graphical presentation of mating's and offspring over multiple generations for a particular trait • Geneticists deduce the mode of inheritance of a trait • See table 17.4 on page 199

30. Page 200 • Symbols • Procedure 17.5

31. 17.3 – page 196: Determine Blood Type for ABO system • We will not work with synthetic blood • Terminology: • Blood Types: A, B, AB, O • Blood Group Genes: I^A I^B i • Rh  (-) and (+) (D gene) • Dd OR Dd = Rh positive (dominant) • dd = Rh negative (-) (recessive)

32. Agglutination • Clumping. NOT clotting • Occurs when blood mixed with an antiserum • Indicates the presence of a the respective antigen on rbc’s

33. continued • Blood Group • A  anti b in plasma (naturally occurring antibodies) • B  anti b in plasma • AB  no anti a or anti b • O  has both anti a and anti b

34. Rh (-) (+) A B AB O