Mendel Essay, Research Paper

Mendel brought considerable insight to his studies. One of the most important decisions he made was to work in a system that was genetically simple as possible. His use of pure-breeding strains of pea plants is indicative of his quest for this simplicity.”*

Mendel used pea plants in his experiments because they were cheap, available, easy to grow, and most importantly, genetically simple. He made these choices out of common sense, to make observation and research easier to accomplish, which is needed when a scientist is beginning research from ground zero. Mendel was a smart guy!

One genetic advantage that pea plants have over other organisms is that they have a short generation time, which means that the children can grow to have kids of their own quickly. This was important to Mendel because he could conduct many more experiments with many more generations by using pea plants.

Another great genetic advantage that Mendel’s pea plants possessed was that they were hermaphroditic organisms. A hermaphrodite, from the Greek derivation, means that an organism possesses both male and female sets of sex organs. Thus, the pea plants could self-fertilize, which is very unusual of organisms. This does not means that the plants were asexual, only that they could reproduce without the help of outside assistance. This is advantageous to Mendel because he wouldn’t have to worry about mating the pea plants, because they could do that themselves very easily. Also, in determining the percentage of inheritance from the mother and the father, Mendel needed only to switch the sexes of the pea plants by keeping or removing the plant’s stamen, or male reproductive organ.

By using pure-breeding strains of pea plants in his experiments, Mendel created a very simple, and thus easy way of studying the genetics and heredity of organisms. Pure-breeding pea plants are plants which possess either all dominant or all recessive traits. This is beneficial in the F1 generation because the results can be easily attained by using a Punnet Device and Mendel’s five-step process. Hybrid trait crosses would be more difficult just because they are hybrid; part dominant and part recessive. The more hybrid a parent, the more complex the next generation. After a few generations, the results are very confusing, which is why Mendel chose to use only pure-breeding strains of pea plants in his experiments and research.

A genetically complex organism would make Mendel’s discoveries of new genetic ideas very difficult.

Instead, by using a simple lifeform, much new information could be collected and used. Mendel was very smart to chose pea plants, with a simple genetic system, over other, more complex systems.

2.(SEE FIGURE G.1)

Mendel created an easy and fun five-step process to use in his pea plant experiments and to discover and research the ratios of offspring produced by any two parents. G.B.E. students also find this process to solve any genetics problems diabolic old instructors might throw their way.

The first step of this process is to physically draw the two parents involved in the experiments. This drawing is also known as a phenotypic analysis, and is important to the scientist to easily recognize the individuals involved in the experiment, and the traits they possess. The drawing of the parents should be drawn to make the traits obvious, and their phenotypic traits should be written clearly. The parents should also be given sexes, male or female. Mendel’s pea plants were hermaphroditic, possessing both male and female traits, so changing them around would cause no change in the experiment’s results. Also, by exchanging the sexes of the pea plants, Mendel later discovered what percentage of inheritance the mother and father give to the offspring.

The second step of the execution process is to ascertain, or make certain, the genotypes of the parents. These genotypes are represented by capital and lowercase letters, and are used to restate the traits possessed by the parents. They are also used to determine the dominance or recessiveness of the traits. A dominant trait is represented by a capital letter, the first letter of the dominant phenotype. A recessive trait is represented by a lower-case letter, also the first letter of the dominant phenotype. Pure-bred or true-bred specimens’ genotypic analysis consists of either two capital letters (dominant) of two lower-case letters (recessive). Only a hybrid, or F1 parent’s genotypic analysis consists of both a capital and lower-case letter (dominant).

The third step of this simple five-step process is to identify and draw the gametes that can be made by each parent of the experiment. The number of possible gametes that can be made by the cross of two parents depends on the parents’ genotypic analysis. If the parent is pure-bred, only one type of gamete can be produced, but two gametes can be produced if the parent is hybrid. One letter only of the genotype is written inside either a sperm or an egg, depending on the sex of the plants. There can either be one or two possible gametes for each parent. By drawing and identifying these gametes, the scientist can easily determine the sex of the parents and those parents’ possible gamete outcomes.

The fourth step of this process is my favorite, and I now know how to execute it correctly. This step involves drawing a Punnet Device to determine and show clearly all possible combinations of all possible gametes. The Punnet Device is not always a square because it shows no redundancies for easier comprehension of the scientist and public. The possible gametes, written in genotypic form, are placed on the outside of the device. These gametes are then combined to discover the combinations of gametes and are written inside the device. With two parents, there are usually one, two, or four boxes involved in this step.

The fifth and final step of Mendel’s process involves conducting phenotypic and genotypic analysis of the offspring. These results are always written in ratio form to show the possibilities of the offspring. The first result is written in phenotypic, or word form. The second result is written in genotypic, of letter form, and both results show the ratio or percentage analyses of the offspring of this experiment.

There you have it! Although hard to explain, Mendel’s five-step process allowed a fun and easy way to discover the ratio of offspring produced by two parents. Students can also use this easy process to their advantage. Yeah!

3.(SEE FIGURE G.2)

I successfully used Mendel’s five-step process to determine the expected result of a cross between a pure-breeding, smooth-seed plant and a pure-breeding, wrinkled-seed specimen.

First, I drew the two parent plants, and labeled one pure-bred smooth-seed and one pure-bred wrinkled-seed. I clearly drew one plant with very smooth seeds and one plant with very exaggerated wrinkled seeds. I also labeled the smooth-seed plant female and the wrinkled-seed male, but I could have switched the two sexes due to the pea plant’s hermaphroditicy. I then could easily recognize the two parents involved in this cross. I needed to glance back at this drawing later in my process.

Secondly, I ascertained, or made certain the genotypes of the two parents involved. The pure-breeding, smooth-seed plant was represented by SS because smooth seeds are dominant over wrinkled seeds. An “s” was used because the first letter of the dominant phenotype, smooth, is indeed “s.” The pure-breeding, wrinkled-seed plant was represented by ss because wrinkled seeds are recessive to smooth seeds. Again, and “s” was used because it is the first letter of the dominant phenotype. I was then certain of the genotypes I could work with in my process.

The third step of Mendel’s process involved identifying and drawing the gametes made by each parent. Since the smooth-seed plant was female, I drew an egg with the letter S in the center. I used only one letter because only one possible gamete can occur at a time. There was also only one possible gamete, so I needed only to draw one egg. I then proceeded to draw a male gamete, or sperm cell with the letter s in the center. Again, only one possible outcome was used at a time, and from this parent only one outcome could possibly occur.

I was then ready to execute Mendel’s Punnet Device, in this case a one-squared square, to show all possible combinations of all possible gametes. On the side of the device I wrote an S to represent the female, smooth-seed gamete possibility, and on the top I wrote an s to represent the male, wrinkled-seed gamete possibility. I then combined the two possibilities to determine the possible outcome of the cross, in this case, Ss. I didn’t need to write the same answer in four squares of the device, because redundancies are inconvenient and silly. Instead, the inside of the device showed the one possible outcome of the cross of these two parents.

In my fifth and final step, I wrote phenotypic and genotypic analyses of the offspring, using ratios in my analyses to determine the percentage of different outcomes possible. I concluded that the outcomes of the cross were all smooth-seed plants, which is indeed a phenotypic ratio. The genotypic ratio of the offspring was all Ss, meaning all smooth children were produced.

Now I have determined the result of a cross between a pure-breeding , smooth-seed plant and a pure-breeding, wrinkled-seed specimen. All outcomes of this cross are smooth-seed plants, or Ss plants.

4.I successfully used Mendel’s five-step process to determine the expected result of a cross between a male plant from the F1 generation produced in the cross from #3, and a female, pure-breeding, wrinkled-seed specimen.

First, I drew the two parent plants, and labeled one a smooth-seed plant from the F1 generation and one a pure-bred wrinkled-seed. I clearly drew the first plant with very smooth seeds and the second with very exaggerated wrinkled seeds. I also labeled the smooth-seed plant male and the wrinkled-seed female because I was told of those sexes in the instructions. Note that pea plants are hermaphroditic, so the sex is really unimportant to the outcome and experiment. By drawing the two plants, I could then easily recognize the two parents involved in this cross. I needed to glance back at this drawing later in my process.

Secondly, I ascertained, or made certain the genotypes of the two parents involved. The F1, smooth-seed plant was represented by Ss because the offspring of the previous cross were all hybrid, thus having a hybrid genotypic analysis, Ss. An “s” was used because the first letter of the dominant phenotype, smooth, is indeed “s.” The pure-breeding, wrinkled-seed plant was represented by ss because wrinkled seeds are recessive to smooth seeds. Again, and “s” was used because it is the first letter of the dominant phenotype. I was then certain of the genotypes I could work with in my process.

The third step of Mendel’s process involved identifying and drawing the gametes made by each parent. Since the smooth-seed plant was male, I drew one sperm cell with the letter S in the center and another sperm cell with the letter s in the center. I used only one letter in each cell because only one possible gamete can occur at a time. There were two possible gametes, so I needed to draw two sperm cells. I then proceeded to draw a female gamete, or egg, with the letter s in the center. Again, only one possible outcome was used at a time, and from this parent only one outcome could possibly occur.

I was then ready to execute Mendel’s Punnet Device, in this case a two-squared device, to show all possible combinations of all possible gametes. On the side of the device I wrote an S and an s to represent the two male, smooth-seed gamete possibilities, and on the top I wrote one s to represent the one female, wrinkled-seed gamete possibility. I then combined the two possibilities to determine the possible outcomes of the cross, in this case, Ss and ss. I didn’t need to write the same answers twice in the squares of the device, because redundancies are inconvenient and silly. Instead, the inside of the device showed the two possible outcomes of the cross of these two parents.

In my fifth and final step, I wrote phenotypic and genotypic analyses of the offspring, using ratios in my analyses to determine the percentage of different outcomes possible. I concluded that the outcome of the cross was one smooth-seed plant to one wrinkled-seed plant, which is indeed a phenotypic ratio. The genotypic ratio of the offspring was one Ss plant to one ss plant, meaning half of the offspring were smooth and half were wrinkled.

Now I have determined the result of a cross between an F1 generation, smooth-seed plant and a pure-breeding, wrinkled-seed specimen. Half of the offspring of this cross were smooth, and the other half were wrinkled.