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

3. Extensions to Mendelian Inheritance

Understanding Independent Assortment

Genetics

3. Extensions to Mendelian Inheritance

Understanding Independent Assortment

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3:29 minutes

Problem 30b

Textbook Question

A male and a female are each heterozygous for both cystic fibrosis (CF) and phenylketonuria (PKU). Both conditions are autosomal recessive, and they assort independently.
What proportion of the children will have either PKU or CF but not both?

Verified step by step guidance

Step 1: Understand the genetic basis of the problem. Both cystic fibrosis (CF) and phenylketonuria (PKU) are autosomal recessive conditions, meaning a child must inherit two recessive alleles (one from each parent) to express the condition. Since the traits assort independently, we can use the principles of Mendelian genetics and a Punnett square for each trait.

Step 2: Construct a Punnett square for CF. Each parent is heterozygous (genotype: Cc), where 'C' is the dominant allele and 'c' is the recessive allele. The possible offspring genotypes are CC, Cc, Cc, and cc. Only the 'cc' genotype results in CF.

Step 3: Construct a Punnett square for PKU. Each parent is heterozygous (genotype: Pp), where 'P' is the dominant allele and 'p' is the recessive allele. The possible offspring genotypes are PP, Pp, Pp, and pp. Only the 'pp' genotype results in PKU.

Step 4: Determine the probability of having either CF or PKU but not both. Use the principle of independent assortment to calculate the combined probabilities. First, calculate the probability of having CF (cc) and not PKU (not pp), then calculate the probability of having PKU (pp) and not CF (not cc). Add these probabilities together.

Step 5: Express the final proportion. The probabilities calculated in Step 4 represent the proportion of children who will have either CF or PKU but not both. Ensure the calculations account for all possible combinations of genotypes and their respective probabilities.

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Key Concepts

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

Autosomal Recessive Inheritance

Autosomal recessive inheritance refers to a pattern where two copies of a mutated gene, one from each parent, are necessary for an individual to express a trait or disorder. In the case of cystic fibrosis (CF) and phenylketonuria (PKU), both conditions require that an individual inherits two recessive alleles to exhibit symptoms. If an individual has one normal and one mutated allele, they are carriers but do not show the disease.

Independent Assortment

Independent assortment is a genetic principle stating that alleles for different traits segregate independently of one another during gamete formation. This means that the inheritance of one trait, such as CF, does not influence the inheritance of another trait, like PKU. This principle allows for a variety of genetic combinations in offspring, which is crucial for calculating probabilities in genetic crosses.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two individuals. By organizing the possible gametes from each parent, it allows for the visualization of potential genotypes and phenotypes of the offspring. In this scenario, a Punnett square can help determine the proportions of children who will inherit either PKU or CF, but not both, by analyzing the combinations of alleles from the heterozygous parents.

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