Mendelian genetics ( Mendel's pea plants experiments)

GENETICS

• Gregor Mendel
• 3 MENDEL LAWS & BASIC VOCABULARY
• Genetics vocabulary

VIDEO :  How Mendel´s pea plants experiment helps us understand genetics 3:06min https://www.youtube.com/watch?v=Mehz7tCxjSE   CONCEPTS RELATED TO GENETICS Heredity  // Genetics  //  Alleles Dominant allele or trait // Recessive allele or trait //  Phenotype  // Genotype    // Traits // Hybrid // Law of dominance //  Law of segregation /  Homozygous organism // Heterozygous organism // Monohybrids  // Dihybrid cross  // Dihybrids   VIDEO :  Genes and  Alleles ( Amoeba sisters ) 8:06min https://www.youtube.com/watch?v=pv3Kj0UjiLE

Gregor Mendel - Scientist | Mini Bio | BIO (Embed)

GREGOR MENDEL

Caption: : VIDEO Gregor Mendel the Scientist 2:35min

In 1843, at the age of 21 Gregor Mendel entered a monastery in Brunn, Austria. His task of tending the garden gave him time to think and observe the growth of many plants. In 1851, he entered the University of Vienna to study science and mathematics.  His mathematic course s included training in statistics what later proved valuable in his research on heredity. When Mendel returned to the monastery he taught in a high school and also kept a garden plot. Although he studied many plants, he is mostly remembered for his experiments with Pisum sativum a species of garden peas.  

Mendel observed seven characteristics (heritable feature) of pea plants. Each characteristic occurred in two contrasting traits – genetically determined variant of a characteristic -. The pea characteristics and traits that Mendel experimented with were: 1. Plant height 2. Flower possition 3. Pod color 4. Pod appereance 5. Seed texture 6. Seed color 7. Flower color

Mendel's pea plants experiment

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Caption: : Mendel experiemented with two constrasting traits for each of seven characteritics of pea plants as shown in the above chart.

Mendel initially studied each characteristic and its contrasting traits individually. He began by growing plants that were true- breeding for each trait by producing pure, true- breeding plants by self- pollinating the plants for several generations, until he was sure of producing true- breeding plants for a trait ( pure plants that will always produce offspring with that trait when self- pollinating)   After this initial experiment, Mendel started cross- pollinating pairs of plants that were true- breeding for contrasting traits of a single characteristic. P generation ( parent plants )   For example, he pollinated a pure purple flowers pea plant with the pollen of another pure white flowers pea plant, to count and record the number of offspring produced by this crossing.  First  generation (Generation F1). Then, he let the first generation (F1) of plants to self-pollinate and did the same: Counting and recording their offspring – second generation (Generation F2) as shown in the image.   Mendel performed hundreds of crosses and documented the results of each by counting and observing the resulting traits in the offspring of both generations F1 and F2

Mendel's pea plants experiments

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Caption: : F1 generation 100% offspring were purple flowered , while in the F2 generation just 75% were purple flowered and the fourth individual was white flowered ( 25% )

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Mendel's pea plants experiments

Mendel cross-pollinates a pure tall pea plant and a pure short pea plant.     All offspring of the first generation F1 are born tall. 100% of the offspring show one of the parents’ traits.Mendel causes  the first generation to self- pollinate.     Out of every four offspring of the second generation F2, 3 offspring are found to be tall (¾ 75% Tall) while only one plant is found to be short (¼ 25% short).

Caption: : Mendel found the same pattern for each of the sevent traits he experimented with

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Mendel's pea plants experiments

Mendel noticed how in  a cross of parents that are pure for contrasting traits, only one form of the trait appeared in the next generation (F1).     While Mendel was crossing (reproducing) his pea plants (over and over again), he noticed something interesting: When he crossed pure tall plants with pure short plants, all the new pea plants (referred to as the F1 generation) were tall.   Similarly, crossing pure yellow seeded pea plants and pure green seeded pea plants produced an F1 generation of all yellow seeded pea plants.    The same was true for the other traits he experimented with

Caption: : Mendel found the same pattern for each of the sevent traits he experimented with

Gregor Mendel (Embed)

Mendel´s observations and careful records made him hypothesize that something within the pea plants controlled the characteristics observed. He called these controls factors and hypothesized that each trait was inherited by means of a separate factor.  Because the characteristics studied had two alternative forms, he reasoned that a pair of factors must control each trait. From these observations, he concluded:   Law of dominance:  The trait appearing on the first generation F1 was controlled by a dominant factor as it masked or dominated the factor for the other trait in the pair.  The trait that does not appear on the first generation but does on the second (F2 generation) is controlled by a recessive factor. Law of segregation: The paired factors separate (segregate) during the formation of reproductive cells. That is, each reproductive cell receives one factor of each pair, thus when two gametes fuse and combine, the offspring have two factors for each characteristic. Law of independent assortment:  Mendel also crossed plants that differed in two different characteristics, such as flower color and seed color for example. The data from these crosses showed that traits produced by dominant factors do not necessarily appear together and different traits are inherited independently.

Mendel's conclusions

Caption: : Teacher's PET : Gregor Mendel 4:01min

So far we have considered one trait at a time: height (tall or short), seed shape (round or wrinkled), pod color (green or yellow) at a time. Mendel noticed during all his work that the height of the plant and the shape of the seeds and the color of the pods had no impact on one another.  In other words, being tall didn't automatically mean the plants had to have green pods, nor did green pods have to be filled only with wrinkled seeds. Different traits seem to be inherited INDEPENDENTLY. In this law the emphasis on the word "different" is considerably important.   Nine times out of ten, in a question involving two different traits, your answer will be "independent assortment".  Independent assortment helps account for the many genetic variations observed in plants animals, and other organisms – even when they have the same parents. Punnet squares that illustrates this law involve what's known as a "dihybrid cross", meaning that the parents are hybrid for two different traits.   In Mendel's third law of inheritance : Independent assortment it is important to consider :    Different traits seem to be inherited INDEPENDENTLY. Alleles for different traits are distributed to sex cells (& offspring) independently of one another. Punnet squares that illustrates this law involve what's known as a "dihybrid cross", meaning that the parents are hybrid for two different traits.  

Mendel's 3rd law : Independent assortment

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Caption: : Mendel's laws synthesis