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Sagot :
Complete question:
1. You found a new species of garden pea and have decided to repeat Mendel’s experiments. You have obtained two true-breeding pea plants that are tall (T) with yellow pods (g), and short (t) with green pods (G), respectively. Capital letters indicate dominant traits.
a. What is the genotype and phenotype of the F1 generation? (2p)
b. You allowed self-fertilization in F1 generation and obtained F2 generation. Using Punnett square to obtain the phenotypes, genotypes and their respective ratios. (4p)
2. If you obtained 1248 offspring in the F2 generation in Question 1, calculate how many offspring of each phenotypic class you would expect to have. (4p)
3. When you finish questions 1 and 2, under what assumption/hypothesis did you perform your analysis/calculation? Is there an alternative assumption/hypothesis, which may result in a different conclusion? If yes, what is the alternative assumption/hypothesis and what kind of offspring and in what numbers do you expect to obtain? (4p)
4. You only need to answer A or B to get this 6p. Please indicate which question you are answering. In your experiment, you found the following offspring only: Tall green: 626 offspring. Tall yellow: 313 offspring. Short green: 309 offspring.
A: If you stay with your original hypothesis/assumption, test it using chi2 test and analyze the result (whether you want to reject the hypothesis and why).
B: If you believe that the alternative hypothesis fits better with your data, test it using chi2 test and analyze the result (whether you want to accept the hypothesis and why).
Answer:
1) a. 100% of the progeny will be dihybrid, TtGg, exhibiting the phenotype
Tall plants with green pods.
b. F2 Gentotype:
- 1/16 TTGG
- 2/16 TTGg
- 1/16 TTgg
- 2/16 TtGG
- 4/16 TtGg
- 2/16 Ttgg
- 1/16 ttGG
- 2/16 ttGg
- 1/6 ttgg
F2 Phenotype:
- 9/16 Tall plants with green pods (T-G-)
- 3/16 Tall plants with yellow pods (T-gg)
- 3/16 Short plants with green pods (ttG-)
- 1/16 Short plants with yellow pods (ttgg)
Phenotypic ratio → 9:3:3:1
2) T-G- → 702 individuals
T-gg → 234 individuals
ttG- → 234 individuals
ttgg → 78 individuals
3)
- Null Hypothesis: The population is under Hardy-Weinberg equilibrium. The alleles of this population assort independently.
- Alternative Hypothesis: The population is not in equilibrium. Alleles do not assort independently.
4) a. There is enough evidence to reject the null hypothesis, meaning that the difference between the observed number of individuals and the expected ones is statistically significant. The population is not under equilibrium H-W. Alleles do not assort independently.
Explanation:
1) 1st Cross: True-breeding tall (T) with yellow pods (g) pea plant with a short (t) with green pods (G) plant
- Tall and Green pods are the dominant traits,
- Short and yellow pods are recessive traits.
Parentals) TTgg x ttGG
Gametes) Tg, Tg, Tg, Tg tG, tG, tG, tG
F1) 100% of the progeny will be dihybrid, TtGg, exhibiting the phenotype
Tall plants with green pods.
2nd Cross: F1 self-fertilization
Parentals) TtGg x TtGg
Gametes) TG, Tg, tG, tg
TG, Tg, tG, tg
Punnett square) TG Tg tG tg
TG TTGG TTGg TtGG TtGg
Tg TTGg TTgg TtGg Ttgg
tG TtGG TtGg ttGG ttGg
tg TtGg Ttgg ttGg ttgg
F2) Gentotype:
- 1/16 TTGG
- 2/16 TTGg
- 1/16 TTgg
- 2/16 TtGG
- 4/16 TtGg
- 2/16 Ttgg
- 1/16 ttGG
- 2/16 ttGg
- 1/6 ttgg
Phenotype:
- 9/16 Tall plants with green pods (T-G-)
- 3/16 Tall plants with yellow pods (T-gg)
- 3/16 Short plants with green pods (ttG-)
- 1/16 Short plants with yellow pods (ttgg)
Phenotypic ratio → 9:3:3:1
2) The total number of individuals in the F2 is 1248.
16 ----------------- 1248 individuals --------------- 100% of the progeny
9 T-G- ----------- X = 702 individuals-------------X = 56.25%
3 T-gg ----------- X = 234 individuals ----------- X = 18.75%
3 ttG- ------------- X = 234 individuals ---------- X = 18.75%
1 ttgg ------------- X = 78 individuals ------------ X = 6.25%
3)
- Hypothesis: The population is under Hardy-Weinberg equilibrium. The alleles of this population assort independently.
- Alternative Hypothesis: The population is not in equilibrium. Alleles do not assort independently
4) F2 composed of:
- Tall green: 626 offspring.
- Tall yellow: 313 offspring.
- Short green: 309 offspring.
Tall/Green Tall/Yellow Short/Green Short/Yellow
Observed 626 313 309 0
Expected 702 234 234 78
(Obs-Exp)²/Exp 8.23 26.7 24 78
X² = Σ(Obs-Exp)²/Exp = 8.23 + 23.7 + 24 + 78 = 136.93 ≅ 137
Freedom degrees = genotypes - number of alleles = 9 - 4 = 5
Significance level, 5% = 0.05
Table value/ Critical value = 11.07
X² = 137
X² > Critica value
137 > 11.07
There is enough evidence to reject the null hypothesis, meaning that the difference between the observed number of individuals and the expected ones is statistically significant. The population is not under equilibrium H-W. Alleles do not assort independently.
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