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. Gregor Mendel’s Work • Starting in 1856 Mendel studied peas which he grew in a garden out side the Abbey he lived in. • Showed that the traits he studied behaved in a precise mathematical way and disproved the theory of "blended inheritance.” • Mendel’s work was rediscovered in 1900 by three botanists: • Carl Correns (Germany) • Erich von Tschermak (Austria) • Hugo de Vries (Holland)

3. Why Peas? Mendel used peas to study inheritance because: • True breeding commercial strains were available • Peas are easy to grow • Peas have many easy to observe traits including:

4. Consistency is Good

5. Gene Expression • Each form of the particular gene is an allele. • Alleles can be either • Dominant – always show trait - T • Recessive – only see if dominant trait absent – t • In order to see the trait expressed, 2 alleles must be paired together (one from mom and one from dad) T Tt + t

6. Gene Expression • Genes come in pairs that separate during the formation of gametes (meiosis). • The members of these pairs can be the same (homozygous) or different (heterozygous).

7. Gene Expression • When two alleles are paired we can express them by their phenotype or genotype. • Phenotype – physical characteristics • Ex. Tall, Short, Dark, Round, Wrinkled • Genotype – the allele combination or genes • Ex. AA, Aa, aa, Dd, Rr, rr, tt

8. Using terminology:

9. Results of Mendel’s monohybrid parental cross: “Mendel’s Principle of Dominance” F1 offspring of a monohybrid cross of true-breeding strains resemble only one of the parents. Why? Smooth seeds (allele S) are completely dominant to wrinkled seeds (allele s).

10. Example of Mendel’s Work Smooth x Wrinkled Phenotype P SS ss Genotype Homozygous Dominant Homozygous Recessive All Smooth Clearly Smooth is Inherited… What happened to wrinkled? F1 Ss Smooth is dominant to wrinkled Use S/s rather than W/w for symbolic logic Heterozygous F1 x F1 = F2 possible gametes NEVER use S/W or s/w Punnett Square: S s 3/4 Smooth 1/4 wrinkled F2 S Smooth SS Smooth Ss possible gametes s Smooth Ss wrinkled ss wrinkled is not missing…just masked as “recessive” in diploid state

11. F1 x F1 = F2 F2 possible gametes Punnett Square: S s S Smooth SS Smooth Ss possible gametes s Smooth Ss wrinkled ss Mendel as a Scientist Test Cross: Unknown Smooth x Wrinkled ss possible gametes If Unknown is SS: s s S Smooth Ss Smooth Ss possible gametes Test Progeny All Smooth S Smooth Ss Smooth Ss possible gametes If Unknown is Ss: s s S Smooth Ss Smooth Ss possible gametes Test Progeny Half Smooth Half wrinkled Wrinkled ss s Wrinkled ss

12. Segregation “Mendel’s Principle of Segregation”: • Recessive characters masked in the F1 progeny of two true-breeding strains, reappear in a specific proportion of the F2 progeny. • Two members of a gene pair segregate (separate) from each other during the formation of gametes.

13. Monohybrid Crosses Yielded Consistent Results Therefore, the Principle of Segregation indeed is a general principle of genetics.

14. Probability and Genetics

15. Equation for probability NUMBER OF THINGS YOU ARE LOOKING FOR PROBABILITY = ----------------------------------- TOTAL NUMBER OF THINGS

16. I have quarter in my pocket. What is the probability that I get heads when flipped? Answer: ½ You have a total of 2 sides and 1 of them is heads.

17. I have 3 pennies and 5 nickels in my pocket. If I pull out one coin what is the probability that I get a nickel? Answer: 5/8 You have a total of 8 coins and 5 of them are nickels.

18. Chi-Square Analysis – determine how close your data is to the known probability of occurrence 50 each If I tossed a coin 100 times, how many heads would you expect to get? Tails? What if you didn’t get 50: 50? How would you know if the numbers you got were good enough?

19. Chi-SquareLets look at the chance of flipping heads or tails o – e (d) d2/e Options Observed (o) Expected (e) d2 43-50 = -7 72 = 49 49/50 = .98 Heads 43 50 57-50 = 7 72 = 49 49/50 = .98 Tails 57 50 X2 = 1.96 N (degree of freedom) = # of options – 1 N = 2 - 1 Add this column for X2 N = 1

20. Chi-Square cont. What do I do with these numbers? N = 1 X2 = 1.96 Once the Chi-square and N values are computed, look on the chart. X2 values are in the shaded region N value look here P = about 17% If the probability (P) given in the table is high, it is very likely that this would occur by chance, and we have a good “fit”. If P is low, we conclude that it is not likely that the deviation observed would occur by chance alone.

21. Activity: Probability and Chi-Squares With a partner, get 2 pennies ( or any coin). Toss your coins 100 times. Make sure you record on the chart how many HH, HT and TT you got. Using Chi-Square analysis, how “fit was your data?

23. What is the probability of each landing on heads or tails? Heads 1/2 Tails 1/2 Punnett Squares work in the same manner HH 1/4 HT 1/4 Heads 1/2 HT 1/4 TT 1/4 Tails 1/2 Phenotype: 1/4 Heads/Heads: 1/2 Heads/Tails: 1/4 Tails/Tails

24. Alleles: T = tall t = short What are the possible gametes produced by these parents? Tt T t Phenotype: Tall Tall T ¾ or 75% Tall TT Tt ½ or 25% short Tt Tall Short t Genotype: Tt tt ¼ or 25% TT 2/4 or 50% Tt ¼ or 25% tt

25. Practicing Monohybrid Punnett Squares • Exercise: Punnett Squares • Do numbers 1, 2 and 3 – make sure to include phenotype and genotype ratios • Get each problem checked by me before you move to the next

26. Lab – Corn Genetics