Planet Earth and Its Environment A 5000-million year Journey

Biology in Focus, HSC CourseGlenda Childrawi, Margaret Robson and Stephanie Hollis

Blueprint of LifeTopic 5: Gregor Mendel1DOT POINT(s)outline the experiments carried out by Gregor Mendeldescribe the aspects of the experimental techniques used by Mendel that led to his success

Gregor Mendel (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 Brnn, Moravia (today this town is Brno in the Czech Republic).www.biography.com

Gregor Mendel (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

Gregor Mendel (1822-84)His choice in garden peas (Pisum sativum) 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

Gregor Mendel (1822-84)Mendels 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

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

Gregor Mendel (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) and Alfred Wallace was developing his theory of evolution.

Gregor Mendel (1822-84)Both Darwin and Wallace were unaware of Mendels work at the time. Mendel was aware of Lamarcks (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 Darwins book in 1860 (after Mendel had completed his investigations, but before he wrote his own papers).www.corkfpc.com

Gregor Mendel (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 Mendels work at that stage related to garden pea plants onlyhis 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

Mendels ExperimentsMendel 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

Mendels ExperimentsThe traits he studied were:stem length: tall or shortthe colour of the seed contents: yellow or greenthe colour of seed coat: grey or whitethe shape of the seed: round or wrinkled peasthe colour of the unripe pod: yellow or greenflower position: axial or terminalpod shape: inflated or constricted.world.eduHandout Garden Pea Characteristics DiagramMendels ExperimentsMendel 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

How Mendel Studied The TraitsOver 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

How Mendel Studied The TraitsWhen Mendel experimentally tested this hypothesis, he obtained quite different and unexpected resultsall of the initial offspring resembled one parent, but in later generations the other parents 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 Mendels laws.www.softchalk.com -How Mendel Studied The TraitsMendels laws: Mendels law of dominance and segregation Mendels law of independent assortment.www.dipity.com

How Mendel Studied The TraitsFor the purposes of the HSC curriculum, we will study in detail Mendels first law of dominance and segregation, developed as a result of his study of monohybrid crosses. Mendels second law of independent assortment is based on dihybrid crosses 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

Mendels Experimental TechniquesMendel used sound scientific experimental techniquehe carried out well-controlled experiments from which he gathered quantitative data to arrive at valid conclusions.www.radio.cz

Mendels Experimental TechniquesMendel 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 Mendels Experimental TechniquesThese 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

Mendels Experimental TechniquesUsing 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

Mendels Experiment in Detail1. 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

Mendels Experiment in Detail2. Mendel then created hybrids by cross-bred two plants with contrasting pure-bred characteristicstall short. He manually transferred pollen between tall and short plants (controlled by removing anthers of recipients)world.edu

Mendels Experiment in DetailWhen 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

Mendels Experiment in DetailThese 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

Mendels Experiment in Detail3. 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

Mendels Experiment in DetailWhen 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

Mendels Experiment in Detail4. 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

Mendels Experiment in DetailMendel 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

Mendels Experiment in Detail5. 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

Mendels Experiment in DetailHe 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 conclusionshis ratios provided supporting evidence for the establishment of his universal laws.www.biography.com

Activity-Handout Table 2.1 which outlines Mendels experiments