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Exploring Mendelian Genetics

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Aggela Polymenis

on 28 January 2016

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Transcript of Exploring Mendelian Genetics

Exploring Mendelian Genetics
Background Info
Much of the knowledge employed by plant breeders is rooted in the work of Gregor Mendel. Working with garden peas, Mendel first discovered the basic principles now known as Mendelian genetics. Mendel inferred the existence of discrete units (genes) that transmit traits from generation to generation, and he hypothesized that there were different forms (alleles) of the genes. We now know that the segregation of traits Mendel observed occurs because traits are determined by discrete sequences of DNA we call genes, and that the different alleles are variations of a single gene.
(Carolina Investigations for AP Biology- Exploring Mendelian Genetics Student Guide, Carolina Biological Supply Company, 2013)
Independent Assortment
This law states that traits are inherited independently of each other. The law only applies to some, but not all patterns of inheritance. This happens from the re-assortment of chromosomes that occurs during meiosis.
Pre- Lab Questions
What is a dominant allele?
-Set of genes that overpower all others when present
What is a recessive allele?
-Set of genes that gets overpowered by the dominant allele.
What is a monohybrid allele?
-Mating between two individuals with different alleles.
What is a dihybrid cross?
-Mating between two different lines that differ in two observed traits. In the Mendelian sense, between the alleles of both these loci there is a relationship of complete dominance - recessive.

To better understand the laws of Mendelian Genetics, and document the growth of fast plants from the brasica species.
-Independent: Genotype of seeds
-Dependent: Phenotype of the offspring
-Constant: Amount of water, temperature, number of seeds planted, amount of light
-Control: Seedlings were grown under the same conditions for the same amount of time
-Qualitative: Chi- Square evaluation
-Quantitative: The number of each phenotype counted
1. A petri dish was filled with water. Two .5x9 cm strips of wet filter paper were used to connect two petri dishes.
2. Two layers of filter paper were placed into the lid of two petri dishes, layered on top of the wicks and wet thoroughly.
3. Dish F1 and F2 were labeled and seeds were evenly spaced in the appropriate dish.
4. Each dish was covered and placed 5-10 cm under the light.
5. Seeds were maintained and checked on daily to ensure filter paper stayed moist and at a constant temperature. After 3 days, phenotypes of each seedling were observed and recorded.
aggela is a nymphomaniac
We performed this lab to solidify the information we learned in class on Mendelian genetics and Punnett squares. In this lab we performed a test cross, determined the dominant versus recessive traits, the genotype of an unknown plant, and predicted the offspring of two crosses using a Mendelian ratio.
Experiment I:
Part I hypothesis:
In part I, two homozygous parents were crossed. One of the parents was tall and green while the other was short and purple. By crossing these two, we were able to determine the dominant and recessive traits. If the cross between P1 x P2 results in all purple plants we can say that purple is the dominant trait, if not then we can say that green is dominant. Similarly, if the same cross results in all tall plants we know that tall is dominant.

Part II hypothesis:
When we cross the tall and purple (TtPp which we determined from part I) F1 generation with another F1 generation we expect the resulting plants to be Mendel's expected ratio of 9:3:3:1 for a heterozygous cross. If we cross the F1 x F1 generation and get something near Mendel’s expected ratio then we have performed this lab correctly.

Experiment II hypothesis:
To determine the genotype (heterozygous or homozygous dominant) of a purple parent plant (once we have determined that purple is the dominant color) we must cross the unknown plant with a green (recessive) plant. If the cross between the two results in all purple plants we can say with confidence that the genotype of the unknown plant is homozygous dominant. If the cross between the two plants results in about half the plants as green and half the plants as purple then one can say with confidence that the phenotype of the unknown plant is heterozygous. So, if the cross between the unknown purple plant and the green plant results in all purple offspring, then the genotype of the unknown plant is homozygous dominant. And if the cross between the unknown purple plant and the green plant results in about half purple offspring and half green offspring, then the genotype of the unknown plant is heterozygous.
In the first phase of the lab we grew a ratio of 6:2:2:1, and we found that the plants were a cross of two heterozygous parents. At first our results were slightly skewed because our counting was biased and done too fast. Later, using our pictures we were better able to distinguish between the phenotypes and categorize our plants. The crossbreeding of the fast plants led to the discovery of the genotypes of the parent generation in the inquiry phase of this lab. This led to the discovery of continued knowledge on the basis of the species of seeds enhancing the underlying themes of Mendelian genetics that we learned in class. With this lab we were able to better understand the definitions of recessive and dominant alleles through the visualization of the fast plants in the parent, F1 and F2 generations. Additionally in Experiment II we learned how to determine the genotype of an unknown dominant plant. One problem I noticed with this lab was the insufficient space under the white florescent light bulbs, because there was not enough room our dishes were pushed out from under the lights or too the side to make room for the other periods dishes. The matter was resolved the next day with area set up with lights. This lab is very applicable in the "real world." Determining the genotype and more particularly the phenotype can be important for determining the probability of passing on a deadly disease to your offspring. Similarly, punnet squares can help determine whether you want to have a baby. Mendelian genetics can also be used in agriculture to create modifications to allow the plant to be more resistant or to create certain plant colors to satisfy customers. Overall, this lab effectively helped us learn the knowledge we read about in the textbook and allowed us to apply it in an experiment.
Results Experiment I
In experiment I we were able to determine two key parts of Mendelian genetics. We learned about dominant and recessive traits and were able to determine which traits are dominant versus which traits are recessive. In this experiment we crossed two parents (homozygous) who were tall and green with short and purple plants to determine that brassica sp. has tall and purple as their dominant traits. From the experiment we determined that the parent generation we crossed was TTpp x ttPP which got us TtPp for all crossed in the F1 generation. By performing this parent to F1 generation cross we noted that tall and purple are dominant traits. In part II of the experiment, we crossed two F1 plants (TtPp) to try to achieve Mendel’s ration of 9:3:3:1. By performing the cross between (TtPp x TtPp) we yielded a result of 11 total plants with a ratio of 6:2:2:1.

Experiment II
In Experiment II we had to determine the genotype of a purple plant {PP (homozygous dominant) or Pp (Heterozygous)}. In this experiment, our cross of the unknown purple plant with a recessive plant would help us in determining the genotype of the unknown plant. Once we crossed our unknown plant with the recessive green plant we determined that the unknown plant was homozygous dominant because all of the resulting plants were purple.
F1 seeds
F2 seeds
4 Petri Dishes with covers
Paper wicks
Filter paper
Cool- white fluorescent light
Punnett Squares
Chi- Square Analysis
Experiment 1: F1
Experiment 1: F2
Experiment 2: Our result
Experiment 2: Another possibility
Experiment 1
Raaghav, Audrey, Aggela, and Sandhiya
Hardy-Weinberg Equation
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