This answer key provides solutions to common genetics practice problems. Understanding these problems is crucial for mastering fundamental genetics concepts. Remember, genetics is a complex field, so thorough understanding of the underlying principles is key to solving more challenging problems.
Disclaimer: This answer key is for educational purposes. Always consult your textbook and instructor for the most accurate and up-to-date information. Variations in problem wording may lead to slightly different approaches.
Mendelian Genetics Problems
Problem 1: Monohybrid Cross
A homozygous dominant tall pea plant (TT) is crossed with a homozygous recessive short pea plant (tt). What are the genotypes and phenotypes of the F1 generation? What are the genotypic and phenotypic ratios of the F2 generation resulting from self-pollination of the F1 plants?
Answer:
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F1 Generation: All offspring will be Tt (heterozygous) and tall (phenotype). Genotypic ratio: 100% Tt; Phenotypic ratio: 100% Tall.
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F2 Generation: A Punnett square reveals the following:
- Genotypes: TT (25%), Tt (50%), tt (25%)
- Genotypic Ratio: 1:2:1 (TT:Tt:tt)
- Phenotypes: Tall (75%), Short (25%)
- Phenotypic Ratio: 3:1 (Tall:Short)
Problem 2: Dihybrid Cross
A plant with round, yellow peas (RRYY) is crossed with a plant with wrinkled, green peas (rryy). Round and yellow are dominant traits. What are the genotypes and phenotypes of the F1 generation? What is the phenotypic ratio of the F2 generation?
Answer:
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F1 Generation: All offspring will be RrYy (heterozygous) with round, yellow peas.
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F2 Generation: A 16-square Punnett square is needed to determine the F2 generation's phenotypic ratio. The phenotypic ratio will be 9:3:3:1, representing:
- 9 Round, Yellow
- 3 Round, Green
- 3 Wrinkled, Yellow
- 1 Wrinkled, Green
Beyond Mendelian Genetics
Problem 3: Incomplete Dominance
In snapdragons, red (R) and white (r) flowers show incomplete dominance. A red snapdragon (RR) is crossed with a white snapdragon (rr). What is the phenotype of the F1 generation? What phenotypes and phenotypic ratios would be expected in the F2 generation?
Answer:
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F1 Generation: All offspring will be Rr and exhibit a pink phenotype (intermediate between red and white).
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F2 Generation: A Punnett square shows the following:
- RR (Red): 25%
- Rr (Pink): 50%
- rr (White): 25%
- Phenotypic Ratio: 1:2:1 (Red:Pink:White)
Problem 4: Sex-linked Inheritance
Hemophilia is a sex-linked recessive trait (located on the X chromosome). A carrier female (XHXh) marries a normal male (XHY). What is the probability that their son will have hemophilia? What is the probability that their daughter will have hemophilia?
Answer:
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Probability of Son having Hemophilia: 50% (XhY)
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Probability of Daughter having Hemophilia: 0% (daughters would be either XHXH or XHXh - carriers).
Advanced Genetics Problems (Optional)
These problems require a deeper understanding of genetic principles and may involve complex crosses or non-Mendelian inheritance patterns. These are excellent challenges for students aiming for mastery.
(Examples of advanced problems could include questions on: gene mapping, linkage, epistasis, polygenic inheritance, pedigree analysis, population genetics, etc.)
This answer key provides a foundational understanding of solving common genetics problems. Remember to practice regularly and consult additional resources to further enhance your comprehension of this fascinating and important biological field.
