Beyond Mendel's Laws of Inheritance: Extending Mendelian Genetics

1. Beyond Mendel’s Lawsof Inheritance Chapter 14

2. Extending Mendelian Genetics • Mendel worked with a simple system • peas are genetically simple • most traits are controlled by a single gene • each gene has only 2 alleles, 1 of which is completely dominant to the other • The relationship between genotype & phenotype is rarely that simple

3. Incomplete Dominance • when one allele is partially dominant over the other • hybrids have “in between” appearance • RR = red flowers • rr = white flowers • Rr = pink flowers • make 50% less color  RR  R′R′ R = red  RR′ R′ = white RR Rr rr

4. 100% pink flowers 25% red 50% pink 25% white 4 O’clock flowers Incomplete Dominance RR R′R′ Parent generation (P) X true-breeding red flowers true-breeding white flowers 1st generation (F1 hybrids) RR′ RR′ RR′ RR′ 100% self-pollinate 2nd generation (F2) 1:2:1

5. CRCR 25% 25% male / sperm CR CW CRCW 50% 50% CR CRCW female / eggs CWCW CW 25% 25% Incomplete Dominance (alt) % genotype % phenotype CRCW x CRCW CRCR CRCW CRCW CWCW 1:2:1 1:2:1

6. Co-dominance • this time, both alleles are expressed, but they are NOT blended together • RR = red coat color • rr = white coat color • Rr = pink coat color?  RR  WW  RW roancoatcolor R = red W = white

7. Co-dominance • 2 alleles affect the phenotype in separate, distinguishable ways • ABOblood groups • 3 alleles • IA, IB, i • both IA & IB are dominant to i allele • IA & IB alleles are co-dominant to each other • determines presences of oligosaccharides/antigens on the surface of red blood cells

8. 1901 | 1930 Blood Type Compatibility • Matching compatible blood groups • critical for blood transfusions • A person produces antibodies against oligosaccharides in foreign blood • wrong blood type • donor’s blood has A or B oligosaccharide that is foreign to recipient • antibodies in recipient’s blood bind to foreign molecules • cause donated blood cells to clump together • can kill the recipient Karl Landsteiner (1868-1943)

9. Blood Types

10. Blood Type Compatibility

11. Pleiotropy • Most genes are pleiotropic • one gene affects more than one phenotypic character • wide-ranging effects due to a single gene: • dwarfism (achondroplasia) • gigantism vs. acromegaly

12. For Nerd Cred… What was his name in The Princess Bride? C’Mon, all good nerds know this! Acromegaly: André the Giant How about the other wrestler in that picture?

13. Pleiotropy • It is not surprising that a gene can affect a number of organism’s characteristics • consider the intricate molecular & cellular interactions responsible for an organism’s development • cystic fibrosis • mucus build up in many organs • sickle cell anemia • sickling of blood cells

14. Epistasis • One gene masks another • coat color in mice = 2 genes • pigment (C) or no pigment (c) • more pigment (black=B) or less (brown=b) • cc = albino, no matter B allele • 9:3:3:1 becomes 9:3:4

15. Epistasis in Labs • 2 genes: E & B • pigment (E) or no pigment (e) • how dark pigment will be: black (B) to brown(b)

16. Johnny & Edgar Winter Epistasis in People albinoAfricans

17. Polygenic Inheritance • Some phenotypes determined by additive effects of 2 or more genes on a single character • phenotypes on a continuum • human traits • skin color • height • weight • eye color • intelligence • behaviors

18. Nature vs. Nurture • Phenotype is controlled by both environment & genes Coat color in arctic fox influenced by heat sensitive alleles Color of Hydrangea flowers is influenced by soil pH Human skin color is influenced by both genetics & environmental conditions

19. Chapter 14Probability & Genetics

20. Genetics & Probability • Mendel’s laws: • segregation • independent assortment reflect same laws of probability that apply to tossing coins or rolling dice

21. P P P p PP Pp Genetics & Probability • Calculating probability of making a specific gamete is just like calculating the probability in flipping a coin • probability of getting a P gamete? • probability making a P gamete? 50% 100%

22. P p Pp Genetics & Probability • Outcome of 1 toss has no impact on the outcome of the next toss • probability of tossing heads each time? • probability making a P gamete each time? 50% 50%

23. Rule of Multiplication • Chance that 2 or more independent events will occur together • probability that 2 coins tossed at the same time will land heads up • probability of Pp x Pp  pp 1/2 x 1/2 = 1/4 1/2 x 1/2 = 1/4

24. Calculating Dihybrid Probability • Rule of multiplication also applies to dihybrid crosses (as long as you don’t have linked genes on the same chromosome) • heterozygous parents — YyRr • probability of producing yyrr? • probability of producing y gamete = 1/2 • probability of producing r gamete = 1/2 • probability of producing yr gamete = 1/2 x 1/2 = 1/4 • probability of producing a yyrr offspring = 1/4 x 1/4 = 1/16

25. P p Pp sperm egg offspring p P Pp 1/2 x 1/2 = 1/4 1/4 1/4 + 1/2 x 1/2 = 1/4 1/2 Rule of Addition • Chance that an event can occur 2 or more different ways • sum of the separate probabilities • think of all the ways you can roll a 7! • probability of Pp x Pp Pp

26. male / sperm P P PP P p P p p P p p Pp pp P female / eggs p Calculating Probability sperm egg offspring Pp x Pp 1/2 x 1/2 = 1/4 1/2 x 1/2 = 1/4 PP Pp 1/2 x 1/2 = 1/4 Pp pp 1/2 1/2 x 1/2 = 1/4

27. Any Questions??

28. QUESTION OF THE DAY Do you like JEOPARDY?