Mendelian Genetics

1. Mendelian Genetics While assigned to teach, he was also assigned to tend the gardens and grow vegetables for the monks to eat. Augustinian Monk at Brno Monastery in Austria (now Czech Republic) Not a great teacher but well trained in math, statistics, probability, physics, and interested in plants and heredity. Gregor Mendel “Father of Genetics” Mountains with short, cool growing season meant pea (Pisum sativum) was an ideal crop plant.

2. http://academic.evergreen.edu/v/vivianoc/homunculus.gif Contributions in 1860s (US Civil War Era) • Discovered Genes as Particles of Inheritance • Discovered Patterns of Inheritance • Discovered Genes Come from Both Parents • Egg + Sperm = Zygote • Nature vs Nurture • Sperm means Seed (Homunculus) • Discovered One Form of Gene (Allele) Dominant to Another • Discovered Recessive Allele Expressed in Absence of Dominant Allele

3. Mendel worked with peas (Pisum sativum) • Good choice for environment of monastery • Network provided unusual varieties for testing • Obligate self-pollination reproductive system • Permits side-by-side genetic barriers • Cross-pollinations require intentional process • Crosses meticulously documented • Crosses numerically/statistically analyzed • Scientists of 1860s could not understand math • Work lost in journals for 50 years! • Rediscovered in 1900s independently by 3 scientists • Recognized as landmark work!

6. One Example of Mendel’s Work Tall x Dwarf Phenotype P TT tt Genotype Homozygous Dominant Homozygous Recessive All Tall Clearly Tall is Inherited… What happened to Dwarf? F1 Tt Tall is dominant to Dwarf Heterozygous F1 x F1 = F2 possible gametes Punnett Square: D d 3/4 Tall 1/4 Dwarf F2 D Tall TT Tall Tt possible gametes d Tall TT Dwarf tt Dwarf is not missing…just masked as “recessive” in a diploid state… there IS a female contribution.

7. F1 x F1 = F2 F2 possible gametes Punnett Square: T t T Tall TT Tall Tt possible gametes t Tall Tt Dwarf tt Mendel as a Scientist Test Cross: Unknown Tall x Dwarf tt possible gametes If Unknown is TT: t t T Tall Tt Tall Tt possible gametes Test Progeny All Tall T Tall Tt Tall Tt 1/3 of F2 Tall are TT 2/3 of F2 Tall are Tt possible gametes If Unknown is Tt: t t T Tall Tt Tall Tt possible gametes Test Progeny Half Tall Half Dwarf t Dwarf tt Dwarf tt

8. Another Example of Mendel’s Work Green x Yellow Phenotype P yy YY Genotype Homozygous Recessive Homozygous Dominant All Yellow Clearly Yellow is Inherited… What happened to Green? F1 Yy Yellow is dominant to Green Heterozygous F1 x F1 = F2 possible gametes NEVER use G/Y or g/y Punnett Square: Y y 3/4 Yellow 1/4 Green F2 Y Yellow YY Yellow Yy possible gametes y Yellow Yy Green yy Green is not missing…just masked as “recessive” in diploid state

9. F1 x F1 = F2 F2 possible gametes Punnett Square: Y y Y Yellow TT Yellow Yy possible gametes y Yellow yy Green yy Mendel as a Scientist Test Cross: Unknown Yellow x Green yy possible gametes If Unknown is YY: y y Y Yellow Yy Yellow Yy possible gametes Test Progeny All Yellow Y Yellow Yy Yellow Yy 1/3 of F2 Yellow are YY 2/3 of F2 Yellow are Yy possible gametes If Unknown is Gg: y y Y Yellow Yy Yellow Yy possible gametes Test Progeny Half Yellow Half Green y Green yy Green yy

10. Mendel as a Scientist Test Cross: Unknown Yellow x Green yy possible gametes If Unknown is YY: y y Y Yellow Yy Yellow Yy possible gametes Y Yellow Yy Yellow Yy possible gametes If Unknown is Yy: y y Y Yellow Yy Yellow Yy possible gametes y Green yy Green yy Actual Results Decision 3 Yellow 2 Green Yy Yy 2 Yellow 3 Green 1 Yellow 4 Green Yy Small families do not follow expected ratios perfectly! 0 Yellow 5 Green Yy Rare, but it can happen! Yy 4 Yellow 1 Green It only takes 1 green to be sure the unknown is Gg! YY 5 Yellow 0 Green <5% chance unknown is Yy 1/2 • 1/2 • 1/2 • 1/2 • 1/2 = 1/32 You could be wrong (rarely)!

11. After 1900 several scientists tried to replicate Mendel’s crosses using other species including snapdragon. Genetics After Mendel Red Yellow P x PRPR PYPY When these alleles go walking, they both do some talking (codominance)! OK, so we cannot use R/r nor Y/y so we pick a third letter…P for the petal color gene. Notice: we do NOT mix R/Y or r/y! All Orange F1 PRPY F1 x F1 = F2 possible gametes Punnett Square: PR PY F2 PR Red PRPR Orange PRPY This F2 will NOT have a 3:1 ratio of phenotypes. Instead it shows a 1:2:1 ratio! The exception here proves the rule. possible gametes PY Orange PRPY Yellow PYPY

12. In addition to this, there are multiple alleles possible: PR = red PY = yellow p = no pigment The combination of alleles in a diploid determine the flower color: PRPR = red PRPY = orange PYPY = yellow PRp = pink PYp = cream pp = white Human hair color follows a similar pattern: Alleles: HBn = brown HBd = blonde hR = red hbk = black The combinations of these alleles determine the base hair color: HBnHBn = dark brown HBnHBd = sandy brown HBnhR = auburn HBnhbk = dark brown HBdHBd = blonde HBdhR = strawberry blonde HBdhbk = blonde hRhR = red hRhbk = red hbkhbk = black Recessive can be common! Dominant does NOT mean frequent!

13. Another Example of Recessive Being Common: Pisum sativum Garden Peas: green seed, wrinkled seed, dwarf stature, white flower yy rr tt aa In other words: a quadruple double-recessive is the most common garden pea on Earth! Quantitative Inheritance: multiple genes control trait Highest Crop Yield: AABBCCDDEE Intermediate Crop Yield: AabbCCDdEe Lowest Crop Yield: aabbccddee Darkest Skin Color: AABBCCDDEE Intermediate Skin Color: AaBbCcDdEe Lightest Skin Color: aabbccddee AaBbCcDdEe x AaBbCcDdEe can produce a huge range of colors! Yet TV talk show guests argue this point for Maury, etc.

14. Phenotype = Genotype + Environment Crop Yield = Genotype + Minerals + Water + Light - Pests etc. Optimizing these factors determines agricultural productivity…last part of our course! Human Skin Color = Genotype + Sun (UV) Exposure - Aging Factors The sun exposure effect is most obvious in people of intermediate skin base color but everyone can have “tan lines.”

15. Who Gets To Mate With Whom? …Two Extremes Inbreeding Depression: related parents give same recessives to children Hemophilia: Queen Victoria’s Mutation and Diseased Grandchildren Tay-Sachs: Jewish Populations Bipolar: Irish Populations Dog Diseases: German Shepherd hip dysplasia Incest Taboo…but Hybrid Vigor: recessives of one family are “covered” by dominant of other family Wild Corn A x Wild Corn B “Half-breed” is better High Yield Hybrid Corn! Are Human Cultures of “Great Melting Pots” Superior? “Mutt” is best dog!

16. Yet Another Example of Mendel’s Work Wrinkled x Round Phenotype P rr RR Genotype Homozygous Recessive Homozygous Dominant All Round Round is dominant to Wrinkled F1 Rr Heterozygous F1 x F1 = F2 NEVER use W/R or w/r possible gametes Punnett Square: R r F2 R Round RR Round Rr 3/4 Round 1/4 Wrinkled possible gametes r Round Rr Wrinkled rr

17. F1 x F1 = F2 F2 possible gametes Punnett Square: R r R Round Rr Round Rr possible gametes r Round Rr Wrinkled rr Mendel as a Scientist Test Cross: Unknown Round x Wrinkled rr possible gametes If Unknown is RR: w w R Round Rr Round Rr possible gametes Test Progeny All Round R Round Rr Round Rr possible gametes If Unknown is Rr: r r R Round Rr Round Rr possible gametes Test Progeny Half Round Half Wrinkled r Wrinkled rr Wrinkled rr

18. Mendel as a Scientist Actual Results Decision Test Cross: 3 Round 2 Wrinkled Rr Unknown Round x Wrinkled rr Rr 2 Round 3 Wrinkled possible gametes 1 Round 4 Wrinkled Rr If Unknown is WW: r r Small families do not follow expected ratios perfectly! R Round Rr Round Rr 0 Round 5 Wrinkled Rr possible gametes Rare, but it can happen! R Round Rr Round Rr Rr 4 Round 1 Wrinkled It only takes 1 wrinkled to be sure the unknown is Rr! possible gametes If Unknown is Ww: RR 5 Round 0 Wrinkled r r <5% chance unknown is Rr R Round Rr Round Rr possible gametes 1/2 • 1/2 • 1/2 • 1/2 • 1/2 = 1/32 r Wrinkled r Wrinkled rr You could be wrong (rarely)!