Mendel’s Genetics

1. Mendel’s Genetics Monohybrid Cross

2. Gregor Mendel • As discussed last class, he was an Austrian monk • He worked at St. Thomas Monastery • He studied both mathematics and botany

3. Why did he actually Succeed? • He chose the appropriate organism to study • He designed and performed his experiments correctly • Analysis of the data was done properly

4. The Patient • The common pea plant also known as Pisum sativium • It was chosen for 4 reasons • It was commercially available • Easy to grow and mature • The sex organs are entirely enclosed in the flower • Different varieties had different traits

6. Purebred • What is a purebred organism? • It is an organism that has descended from ancestors of a distinct type or breed • Why was this important to Mendel and his pea plants? • This is because he used purebred plants to conduct all of his experiments

7. How did he make sure? • How did Mendel make sure that his organisms (pea plant) were pure bred? • He bred them as everyone else bred plants, and he looked at one trait at a time • He selected from the progeny, only the plants that had the trait that he was looking for • He then bred them together (F1 x F1) and then he continued this for several generations until no more of the other trait showed up

8. What happened Next? • He repeated this for all the other traits until he had pure bred plants with each trait.

9. The first of the Crosses • So what did he end up doing next? • He started to cross breed • He designated the parents as the “p” generations and crossed a true-breeding tall pea plant, with a true-breeding short pea plant • The offspring were of course the F1 generation and he also denoted them as Hybrids

10. That F1 Generation • What do you think he saw? • What was the phenotype of the plants? • All of the plants were tall • What is this type of crossing is called?

11. Cross? • Well what is the Greek word for a single unit? • Well, think back to the first unit, what did we call a single sugar • MONOSACCARIDE • So now what is the Greek word for a single unit? • MONO (Greek word for single or alone)

12. Creatively • Creatively the name given to this type of cross is Monohybrid • It is a single cross between two purebred plants giving us a hybrid species

13. What did his experiment look like?

14. That’s the Phenotype • We have now seen the phenotype • All of the F1 generations plants were tall • What do you think that the genotype must be of the offspring? • First we have to learn some more terms

15. Terms • Homozygous Dominant (TT) – Two alleles for a trait that are the same as a result of pure breeding • Heterozygous (Tt) – Having two alleles for a trait that are different • Homozygous Recessive (tt) - Two alleles for a trait that are the same as a result of pure breeding

16. The First Cross PF1 Tall Short

17. Lets back track • Yesterday we looked at the different combinations of alleles that an individual can have • We also talked about dominance and recessiveness • What did we say the dominant allele was? • What about the recessive allele

18. What were the parents? • The parents that was tall had a double dominant allele • The parent that was short had a double recessive allele • Both of these parents were homozygous

19. When he Crossed • When the parents were crossed, the F1 generation was completely heterozygous • They all expressed the dominant trait, but why? • This was because the dominant allele trumps the recessive allele

20. So the First cross is done, what about the second?

21. Second Cross Genotype

22. Mendelian Ratio • As Mendel completed the experiment, he found that 75% of the offspring of the F1 cross were the dominant (tall) and 25% were the recessive (short) • The Ratio of 3:1 is known as the Mendelian ratio

23. Based on observations, Why did this happen? • Each parent in his F1 Generation starts with two hereditary “factors.” One factor is dominant and the other recessive • The factors separate out in the and only one of the two factors contribute to the phenotype of the offspring

24. Why did this happen? • The offspring inherit one factor from mom and one from dad. If the dominant factor is present, it will be expressed, even if the recessive one is present • The recessive factors will be express only if the recessive factors are present

25. The first Law of heredity • His results gave rise to his first law The law of Segregation

26. The law of segregation • His law of segregation states that inherited traits are determined by pairs of “factors” • These factors segregate in the gametes (after meiosis) • Mendel did not know that his factors were actually genes, we know this today

27. What do we call this?

28. Punnett Square’s

29. What do they do for us? • Well, they are used by geneticists so that they can calculate the expected ratio (probability) and to suggest possible combinations of alleles in the offspring • They also tell us something about the phenotype (the appearance of a trait in an organism)

30. So we saw TT x tt • And for that cross we ended up having a ratio of? • All were Heterozygous (100% - 0%) • What about when we cross the F1 x F1 generations?

31. F1 X F1 • What’s the ratio when we are talking about phenotype? • 3:1 as well, three of the offspring will present the dominant gene while the fourth will present the recessive gene • What about the genotype ratio? • 1:2:1 (one homozygous dominant, two heterozygous, and one homozygous recessive)

32. Example

33. Class Work • Read Pages 123 – 129 • Complete Questions P135, 1-6, 8-16