16 Jun Lab Exercise Lesson 2: Multigenic Mendelian Genetics and Testing Mendel’s Hypotheses
Question
Name: ____________
Lab Exercise Lesson 2: Multigenic Mendelian Genetics and Testing Mendel’s Hypotheses
Lab Preparation
Textbook: Read Chapter 3 (Principles of Genetics, Snustad & Simmons 2012)
Video: Watch Professor Anderson’s Explanation of Punnett Squares (some topics of are important for this week and some are important for future weeks)
Video: Watch Professor Anderson’s Chi-Square Video
Mendel’s Hypotheses
The results from Medel’s experiments lead to hypotheses which other data from genetic crosses could be tested. In this lab, you will identify what the Mendelian hypotheses for monohybrid and dihybrid crosses are. Then you will use these hypotheses to test whether experimental data are consistent with a hypothesis. You will use a chi-square goodness-of-fit test statistic to accept or reject the hypothesis.
Monohybrid Cross- One Trait
Preform the following cross and determine the Mendelian phenotypic and genotypic ratio. Start with two true breeding parents one dominant (G) and one recessive (g) for the color of peas trait in peas. The dominant allele give a green color and the recessive phenotype is yellow. True breeding means there is very little variation in phenotype from one generation to the next and the trait is likely homozygous. This is the parental generation (P). The parental cross produced an F1 generation. The F1 generation offspring were self-fertilized to produce an F2 generation. A Punnett square is a good way to organize your data.
1. What are the genotypes for each parent?
2. What is the genotype and phenotype for the F1 generation offspring (fill in shaded part of table)?
Parent 1 Gametes
Parent 2 Gametes
3. What are the genotypes and phenotypes of the F2 generation (fill in shaded part of table with both genotype and phenotype)?
Parent 1 Gametes
Parent 2 Gametes
4. What is the phenotypic ratio that can be used as a hypothesis for a heterozygous monohybrid cross (cross of heterozygotes for one trait) if the trait follows the properties of Mendelian inheritance?
Dihybrid Cross- Two Traits
Preform the following cross and determine the Mendelian phenotypic and genotypic ratio. Start with two true breeding parents one dominant and one recessive for both a color (G, g) and shape (W, w) traits in peas. True breeding means there is very little variation in phenotype from one generation to the next and the trait is likely homozygous. This is the parental generation (P). The parental cross produced an F1 generation. The F1 generation offspring were self-fertilized to produce an F2 generation. A Punnett square is a good way to organize your data.
5. What are the genotypes for each parent?
6. What is the genotype and phenotype for the F1 generation offspring (fill in shaded part of table and note you may only need a portion of the table)?
Parent 1 Gametes
Parent 2 Gametes
7. What are the genotypes and phenotypes of the F2 generation (fill in shaded part of table with both genotype and phenotype)?
Parent 1 Gametes
Parent 2 Gametes
8. What is the phenotypic ratio that can be used as a hypothesis for a heterozygous dihybrid cross (cross of heterozygotes for two traits) if the traits follow the properties of Mendelian inheritance?
Chi-Square Test
A chi-square test is a way to statistically determine if data fit a hypothesis. For us in genetics that means whether data from a cross fits the hypothesis of Mendelian inheritance. It is based in looking for the number of expected individuals and comparing that to the observed. Once the chi-square statistic is calculated it is compared to a 5% critical value. If the statistic is less than the 5% critical value we will accept the hypothesis of Mendelian inheritance. Conversely if the statistic you calculate is greater than 5% critical value, then you conclude that there is not sufficient evidence to support for the hypothesis of Mendelian inheritance. This is the formula to calculate the chi-square statistic:
Use chi-square test to determine if this data is consistent with Mendelian inheritance for one trait (monohybrid cross) in this example. Remember that the degrees of freedom will be the number of data categories of the offspring in the cross.
9. In sesame, the one-pod condition (P) is dominant to the three-pod condition (p), and normal leaf (L) is dominant over wrinkled leaf (l). The two characters are inherited independently. A cross between two members of the F1 generation produces the following progeny: 318 one-pod normal, 185 one-pod wrinkled, 323 three-pod normal and 184 three-pod wrinkled. Determine, using chi-square analysis whether the data fits the typical Mendelian ratio for F2 generation that you determined above (#8). Show your work (Note: if you are familiar and prefer to do your calculations in Excel you can and paste the table here).
Application: Additional Problems
10. The dominant gene (G) produces green hair in aliens and the recessive gene (g) produces blue hair. Webbed fingers are due to the dominant gene (F) and normal fingers are recessive (f). An alien who was heterozygous for hair color and who had normal fingers had a father with blue hair and webbed fingers and a mother with green hair and webbed fingers. What are the genotypes of all individuals (as completely as possible)? Fill in the table below:
Individual
Phenotype
Genotype
Alien
Green hair, normal fingers
Father’s
Mother’s
11. In Guinea pigs, black hair (B) is dominant over white (b), rough coat texture (R) is dominant over smooth (r), and short hair (S) is dominant over long hair (s). Cross a homozygous black, rough, short-haired Guinea pig and a white, smooth, long-haired one.
What would the phenotype(s) of the offspring be?
If two of the F1 offspring were crossed, what would the phenotypes and phenotypic ratio be?
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