Table of contents

1. Introduction to Genetics51m
2. Mendel's Laws of Inheritance3h 37m
3. Extensions to Mendelian Inheritance2h 41m
4. Genetic Mapping and Linkage2h 28m
5. Genetics of Bacteria and Viruses1h 21m
6. Chromosomal Variation1h 48m
7. DNA and Chromosome Structure56m
8. DNA Replication1h 10m
9. Mitosis and Meiosis1h 34m
10. Transcription1h 0m
11. Translation58m
12. Gene Regulation in Prokaryotes1h 19m
13. Gene Regulation in Eukaryotes44m
14. Genetic Control of Development44m
15. Genomes and Genomics1h 50m
16. Transposable Elements47m
17. Mutation, Repair, and Recombination1h 6m
18. Molecular Genetic Tools19m
- Genetic Cloning
  9m
- Methods for Analyzing DNA
  9m
19. Cancer Genetics29m
- Overview of Cancer
  21m
- Cancer Mutations
  7m
20. Quantitative Genetics1h 26m
21. Population Genetics50m
- Hardy Weinberg
  19m
- Allelic Frequency Changes
  31m
22. Evolutionary Genetics29m

21. Population Genetics

Hardy Weinberg

Genetics

21. Population Genetics

Hardy Weinberg

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2:41 minutes

Problem 30b

Textbook Question

In humans the presence of chin and cheek dimples is dominant to the absence of dimples, and the ability to taste the compound PTC is dominant to the inability to taste the compound. Both traits are autosomal, and they are unlinked. The frequencies of alleles for dimples are D = 0.62 and d = 0.38. For tasting, the allele frequencies are T = 0.76 and t = 0.24.
What are the expected frequencies of the four possible phenotype combinations: dimpled tasters, undimpled tasters, dimpled nontasters, and undimpled nontasters?

Verified step by step guidance

Step 1: Understand the problem. The question asks for the expected frequencies of four phenotype combinations based on the allele frequencies provided. The traits (dimples and PTC tasting) are autosomal and unlinked, meaning their inheritance is independent of each other. The phenotype combinations are: dimpled tasters, undimpled tasters, dimpled nontasters, and undimpled nontasters.

Step 2: Calculate the genotype frequencies for each trait using the Hardy-Weinberg principle. For dimples, the allele frequencies are D = 0.62 and d = 0.38. The genotype frequencies are: P(DD) = (0.62)^2, P(Dd) = 2(0.62)(0.38), and P(dd) = (0.38)^2. Similarly, for PTC tasting, the allele frequencies are T = 0.76 and t = 0.24. The genotype frequencies are: P(TT) = (0.76)^2, P(Tt) = 2(0.76)(0.24), and P(tt) = (0.24)^2.

Step 3: Determine the phenotype frequencies for each trait. For dimples, the dominant phenotype (presence of dimples) is expressed by genotypes DD and Dd, so P(dimpled) = P(DD) + P(Dd). The recessive phenotype (absence of dimples) is expressed by genotype dd, so P(undimpled) = P(dd). For PTC tasting, the dominant phenotype (taster) is expressed by genotypes TT and Tt, so P(taster) = P(TT) + P(Tt). The recessive phenotype (nontaster) is expressed by genotype tt, so P(nontaster) = P(tt).

Step 4: Use the principle of independent assortment to calculate the frequencies of the four phenotype combinations. Multiply the phenotype probabilities for dimples and PTC tasting to find the joint probabilities: P(dimpled tasters) = P(dimpled) × P(taster), P(undimpled tasters) = P(undimpled) × P(taster), P(dimpled nontasters) = P(dimpled) × P(nontaster), and P(undimpled nontasters) = P(undimpled) × P(nontaster).

Step 5: Summarize the results. The expected frequencies of the four phenotype combinations are the values calculated in Step 4. These frequencies represent the proportion of individuals in the population expected to exhibit each phenotype combination.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Mendelian Genetics

Mendelian genetics is the study of how traits are inherited through generations based on the principles established by Gregor Mendel. It involves understanding dominant and recessive alleles, where dominant traits mask the expression of recessive ones. In this context, the presence of dimples and the ability to taste PTC are both dominant traits, which means individuals with at least one dominant allele will express these traits.

Hardy-Weinberg Principle

The Hardy-Weinberg principle provides a mathematical framework for understanding allele frequencies in a population at equilibrium. It states that allele and genotype frequencies will remain constant from generation to generation in the absence of evolutionary influences. This principle is essential for calculating expected genotype frequencies based on known allele frequencies, which is necessary for determining the phenotype combinations in the given question.

Phenotype and Genotype Frequencies

Phenotype frequencies refer to the observable traits of individuals in a population, while genotype frequencies refer to the genetic makeup that determines these traits. In this scenario, the expected phenotype combinations (dimpled tasters, undimpled tasters, dimpled nontasters, and undimpled nontasters) can be calculated using the allele frequencies provided. By applying the principles of Mendelian inheritance and the Hardy-Weinberg equation, one can derive the expected frequencies of these phenotypes.

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Textbook Question

A total of 1000 members of a Central American population are typed for the ABO blood group. In the sample, 421 have blood type A, 168 have blood type B, 336 have blood type O, and 75 have blood type AB. Use this information to determine the frequency of ABO blood group alleles in the sample.

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Textbook Question

A sample of 500 field mice contains 225 individuals that are D₁D₁, 175 that are D₁D₂, and 100 that are D₂D₂.

Is inbreeding a possible genetic explanation for the observed distribution of genotypes? Why or why not?

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Textbook Question

A sample of 500 field mice contains 225 individuals that are D₁D₁, 175 that are D₁D₂, and 100 that are D₂D₂.

Is this population in H-W equilibrium? Use the chi-square test to justify your answer.

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Textbook Question

A sample of 500 field mice contains 225 individuals that are D₁D₁, 175 that are D₁D₂, and 100 that are D₂D₂.

What are the frequencies of D₁ and D₂ in this sample?

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Textbook Question

In humans the presence of chin and cheek dimples is dominant to the absence of dimples, and the ability to taste the compound PTC is dominant to the inability to taste the compound. Both traits are autosomal, and they are unlinked. The frequencies of alleles for dimples are D = 0.62 and d = 0.38. For tasting, the allele frequencies are T = 0.76 and t = 0.24.

Determine the frequency of genotypes for each gene and the frequency of each phenotype.

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Textbook Question

Albinism, an autosomal recessive trait characterized by an absence of skin pigmentation, is found in 1 in 4000 people in populations at equilibrium. Brachydactyly, an autosomal dominant trait producing shortened fingers and toes, is found in 1 in 6000 people in populations at equilibrium. For each of these traits, calculate the frequency of For albinism only, what is the frequency of mating between heterozygotes?

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