Blueprint of Life Topic 5: Gregor Mendel

1. Blueprint of LifeTopic 5: Gregor Mendel Biology in Focus, HSC Course Glenda Childrawi, Margaret Robson and Stephanie Hollis

2. DOT POINT(s) • outline the experiments carried out by GregorMendel • describe the aspects of the experimental techniques used by Mendel that led to his success

3. GregorMendel (1822-84) Gregor Mendel was an Augustinian monk of Austrian origin. He also worked as a teacher and an investigator while living in the monastery in Brünn, Moravia (today this town is Brno in the Czech Republic). www.biography.com

4. GregorMendel (1822-84) He experimented by growing a variety of garden pea plants and recording the resulting ratios of characteristics that appeared in the offspring. In 1856 he began his now-famous research and through his studies he showed that inherited characteristics are passed as discrete ‘units’ from parents to their offspring. thisgrowinglife.blogspot.com

5. GregorMendel (1822-84) His choice in garden peas (Pisumsativum) was critical to his success as he could easily grow them in large numbers, they produced new generations quickly and had easily distinguishable characteristics. He could also control the population and thus fertilisation of each flower. comenius.susqu.edu

6. GregorMendel (1822-84) Mendel’s breakthrough was that he recognised a pattern in the inheritance of characteristics by offspring from their parents and so he proposed a model of inheritance. Using mathematical calculations, he was able to predict the ratios of various types of offspring from any two specific parents. blog.scs.sk.ca

7. GregorMendel (1822-84) This work led him to formulate principles of inheritance which held up to testing and later became known as Mendel’s laws. These laws are applied universally today to describe patterns of heredity and variation in living organisms, a field of biology known as genetics. Mendel’s work marked the start of this branch of biology and so Mendel is referred to as the ‘father of genetics’. www.myspace.com

8. GregorMendel (1822-84) Mendel was working on inheritance in garden peas at the same time that Charles Darwin was writing up his theory of evolution (from results that he had collected over many years) andAlfred Wallace was developing his theory of evolution.

9. GregorMendel (1822-84) Both Darwin and Wallace were unaware of Mendel’s work at the time. Mendel was aware of Lamarck’s (he was the first scientist to be widely acknowledged for a theory regarding evolution) proposal and there is evidence that Mendel had read a copy of Darwin’s book in 1860 (after Mendel had completed his investigations, but before he wrote his own papers). www.corkfpc.com

10. GregorMendel (1822-84) However, Mendel did not seem to make any links between his work and that of Darwin. This is not too surprising if one considers that Mendel’s work at that stage related to garden pea plants only—his work on the inheritance of characteristics in general was only later applied to other organisms, resulting in the development of universal laws of inheritance. thisgrowinglife.blogspot.com

11. Mendel’s Experiments Mendel experimented with garden pea plants, investigating their breeding patterns to determine the inheritance of characteristics (traits). Pea plants were ideally suited because they can be easily grown and cross-bred, have a short life cycle (they are annual plants) and both male and female parts are present in their flowers. www.flowersinisrael.com

12. Mendel’s Experiments The traits he studied were: • stem length: tall or short • the colour of the seed contents: yellow or green • the colour of seed coat: grey or white • the shape of the seed: round or wrinkled peas • the colour of the unripe pod: yellow or green • flower position: axial or terminal • pod shape: inflated or constricted. Handout Garden Pea Characteristics Diagram world.edu

13. Mendel’s Experiments Mendel studied the inheritance of each trait individually (e.g. trait = stem length), investigating the inheritance of one pair of contrasting features at a time (e.g. tall or short stem length). www.takdangaralin.com

14. How Mendel Studied The Traits Over a period of 2 years, Mendel established pure-breeding lines of pea plants which he then crossbred to study the inheritance of their characteristics (traits). At the time, it was believed that if parents with contrasting characteristics for a particular feature were crossed, the offspring would display a ‘blending’ of the characteristics. For example if a tall plant and a short plant were crossed, the expected offspring would be of medium height. www.exploringnature.org

15. How Mendel Studied The Traits When Mendel experimentally tested this hypothesis, he obtained quite different and unexpected results—all of the initial offspring resembled one parent, but in later generations the other parent’s trait would arise, appearing to have ‘skipped a generation’. From his direct counts of resulting plants, Mendel developed mathematical ratios that provided evidence for what are today known as Mendel’s laws. www.softchalk.com -

16. How Mendel Studied The Traits Mendel’s laws: ■ Mendel’s law of dominance and segregation ■ Mendel’s law of independent assortment. www.dipity.com

17. How Mendel Studied The Traits For the purposes of the HSC curriculum, we will study in detail Mendel’s first law of dominance and segregation, developed as a result of his study of monohybrid crosses. Mendel’s second law of independent assortment is based on dihybridcrosses and will only be dealt with in detail in the optional module, ‘Genetics: the code broken?’. We may or may not chose to study this. www.rentmidwest.com

18. Mendel’s Experimental Techniques Mendel used sound scientific experimental technique—he carried out well-controlled experiments from which he gathered quantitative data to arrive at valid conclusions. www.radio.cz

19. Mendel’s Experimental Techniques Mendel controlled the breeding lines of his experiments in the following way: • To ensure pure-breeding lines: over a period of 2 years, Mendel established pure-breeding lines. He ensured that the pea plants would self-pollinate by using plants with flowers that had both male and female parts enclosed within one flower. 12knights.pbworks.com

20. Mendel’s Experimental Techniques These were kept isolated in a greenhouse, to prevent accidental cross-pollination. Mendel bred tall parent plants that gave rise to only tall offspring and short parent plants that gave rise to short offspring, both over several generations. mendel.devildream.com

21. Mendel’s Experimental Techniques Using hundreds of pea plants, Mendel manually transferred pollen, e.g. from the anthers of tall plants to the stigmas of short plants (which had no stamens, to prevent accidental selfpollination). world.edu

22. Mendel’s Experiment in Detail 1. He established 2 pure breeding lines: 1 tall and 1 short. He did this by using male and female parts within the same flower. The offspring of pure-breeding lines all resemble their parents, ensuring that they in turn are pure-breeding for a particular trait (characteristic). The resulting tall or short offspring that are ‘pure-bred lines’ become the P or parent generation in subsequent crosses. www.emc.maricopa.edu

23. Mendel’s Experiment in Detail 2. Mendel then created hybrids by cross-bred two plants with contrasting pure-bred characteristics—tall × short. He manually transferred pollen between tall and short plants (controlled by removing anthers of recipients) world.edu

24. Mendel’s Experiment in Detail When parents that are pure-breeding for contrasting characteristics (such as tallness and shortness) are crossed, the offspring all resemble one parent (in this case, the tall parent). world.edu

25. Mendel’s Experiment in Detail These offspring (the F1 or first filial generation) are termed hybrids (mixed breeds), but they resemble only one parent. Mendel called the characteristic of the parent that they resemble dominant and the other characteristic, which is masked, recessive. In this cross, ‘tall’ is dominant over ‘short’ (recessive). world.edu

26. Mendel’s Experiment in Detail 3. Mendel carried out a monohybrid cross by cross-breeding two F1 individuals that are hybrid for one particular trait. In other words, two hybrid plants from the first filial generation of the previous experiment. Some were allowed to undergo selfpollination, whereas others were crosspollinated, because all were hybrids; a large sample size was used. world.edu

27. Mendel’s Experiment in Detail When two hybrid plants are crossed, one characteristic (dominant) appears three times as frequently in the offspring as the other (recessive) characteristic. That is, the average ratio observed in offspring is 3:1. It appears that one factor that was passed down from the original parent generation became ‘masked’ or hidden in the F1 generation and then reappeared in the F2 generation. world.edu

28. Mendel’s Experiment in Detail 4. Mendel derived principles based on mathematical calculations. He showed that these ratios arise if an individual possesses two ‘factors’ for any characteristic, where one is dominant over the other, and these two factors segregate or separate when they are passed from parent to offspring. world.edu

29. Mendel’s Experiment in Detail Mendel proposed that during reproduction, the two factors segregate and each passes into a separate gamete. When two gametes combine during fertilisation, each contributes one factor to the newly formed offspring. Mendel used statistics to calculate the probability of different combinations of factors pairing in offspring and he obtained a 3:1 ratio. world.edu

30. Mendel’s Experiment in Detail 5. Mendel made direct counts of the resulting offspring, giving quantitative data, which he collated and analysed to identify patterns and trends. Mendel applied logical thinking and a mathematical model to the data he had gathered, leading to his valid conclusions. www.flickr.com

31. Mendel’s Experiment in Detail He used a mathematical model to explain the phenomenon of inheritance and to make predictions for future crosses (which he later tested successfully). He justified all of his inferences and conclusions—his ratios provided supporting evidence for the establishment of his universal laws. www.biography.com

32. Activity -Handout Table 2.1 which outlines Mendel’s experiments