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

7. DNA and Chromosome Structure

DNA as the Genetic Material

Genetics

7. DNA and Chromosome Structure

DNA as the Genetic Material

Previous problemNext problem

1:44 minutes

Problem 31a

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 the recessive allele at the locus

Verified step by step guidance

Understand the problem: Albinism is an autosomal recessive trait, meaning individuals with the condition must have two copies of the recessive allele (aa). The frequency of individuals with albinism in the population is given as 1 in 4000. This corresponds to the genotype frequency of homozygous recessive individuals (q²). Similarly, for brachydactyly, an autosomal dominant trait, the frequency of affected individuals is 1 in 6000, which includes both heterozygous (Aa) and homozygous dominant (AA) genotypes.

For albinism, use the Hardy-Weinberg equation to calculate the frequency of the recessive allele (q). The Hardy-Weinberg equation is p² + 2pq + q² = 1, where p is the frequency of the dominant allele, q is the frequency of the recessive allele, p² is the frequency of homozygous dominant individuals, 2pq is the frequency of heterozygous individuals, and q² is the frequency of homozygous recessive individuals. Since q² = 1/4000, calculate q by taking the square root of q²: q = √(1/4000).

For brachydactyly, note that the frequency of affected individuals (1/6000) includes both heterozygous (2pq) and homozygous dominant (p²) genotypes. To calculate the frequency of the recessive allele (q), first determine the frequency of unaffected individuals (q²), which is the complement of the affected frequency: q² = 1 - (frequency of affected individuals). Then calculate q by taking the square root of q²: q = √q².

Once you have calculated q for both traits, you can also calculate the frequency of the dominant allele (p) using the relationship p + q = 1. Rearrange this equation to solve for p: p = 1 - q.

Summarize the results: The frequency of the recessive allele (q) for albinism and brachydactyly can be determined using the Hardy-Weinberg principle. Ensure that all calculations are consistent with the assumptions of Hardy-Weinberg equilibrium, such as random mating, no mutation, no migration, no selection, and a large population size.

Verified video answer for a similar problem:

This video solution was recommended by our tutors as helpful for the problem above

Video duration:

Play a video:

Was this helpful?

Key Concepts

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

Hardy-Weinberg Principle

The Hardy-Weinberg Principle provides a mathematical framework for understanding allele frequencies in a population at genetic 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 allele frequencies, particularly in traits governed by simple Mendelian inheritance.

Autosomal Recessive Inheritance

Autosomal recessive inheritance occurs when a trait is expressed only when an individual has two copies of the recessive allele. In the case of albinism, the absence of skin pigmentation results from inheriting two recessive alleles. Understanding this inheritance pattern is crucial for calculating the frequency of the recessive allele in a population.

Allele Frequency Calculation

Allele frequency calculation involves determining the proportion of a specific allele within a population. For recessive traits, the frequency of the recessive allele can be derived from the proportion of individuals expressing the trait, using the formula q^2 = frequency of recessive phenotype. This calculation is vital for understanding genetic variation and predicting the likelihood of traits in future generations.

Watch next

Master History and Experiments with a bite sized video explanation from Kylia

Start learning